Britbike forum

Correct needle for 1000-series Concentrics?

Posted By: Magnetoman

Correct needle for 1000-series Concentrics? - 03/13/19 9:52 pm

Question: Do 1000-series Amal Concentrics use the same needles as 900-series?

Making a long story long, I had all sorts of carburetor problems when I got my Catalina until I finally discovered, almost by accident, that its large 'D' Monobloc had a too-short 'C' needle from a smaller carburetor. Replacing it with the correct needle made all the difference.

My Competition now sits with its transformation 99.9% completed from a "Clubman" with clip-ons and 6-gal. Lyta tank to more of a modern cafe racer with low handlebars, 2-gal. alloy tank, and rear sets. However, even though I know enough to leave well enough alone, I've decided to significantly alter the Concentric carburetor that's on it. This only can be described as a self-inflicted wound.

When I got the bike 24 years ago I did quite a bit of work on it before it was ready to ride. At some point during that process I removed the GP and replaced it with a 36 mm 1036 Concentric and also around that time turned it over to the now-deceased guy who owned the BB and Catalina I now have to sort out some issues. He got the carburetor working well, which is what I should leave alone. But...

The carburetor is in 2-stroke configuration. As the first photograph shows, a 4-stroke jet holder (bottom) is longer because it is said that otherwise the main jet would interfere with the longer 4-stroke needle. Not as obvious, the needle jets also are different as suggested by the hole in the four-stroke version. In addition, as the second photograph shows, the spray tube in the bottom of the bore is slash-cut in the 2-stroke version at the left but flat on top in the 4-stroke at the right. This can be changed by pushing the old one out and the new one in, and the jet holder and needle jets are easy to switch as well.

This brings us to my question about the needle. The "Carburetor" tab in my two-volume bespoke Gold Star shop manual is 3/4"-thick (~190 pages), containing everything useful I've run across for GPs, TTs, Monoblocs and Concentrics. Unfortunately, there is relatively little about the 1000-series Concentric, and nowhere can I find if they use the same needles as the 900-series. It's a bigger carburetor so it wouldn't surprise me if the needles were different, but maybe they were the same(?). Having been burned once by a too-short needle, I'm proceeding cautiously.

Correction: As the third photograph shows the needle I took from a 4-stroke 932 is a tiny bit longer than the needle that was in a 1038 Concentric (2.678" vs. 2.644") I have on the shelf. However, the needle that was in my 1036 is only 2.297" long (i.e. ~0.38" shorter than either in this photograph) with 1 groove in it, which a table tells me is a "rich" 2-stroke needle for a 900 series. For what it's worth, the needle from the 932 has 2 rings on it so it is a "standard" 4-stroke needle, while the one from the 1038 has the letter (or number) 'O' stamped at the top which the Amal site tells me is a 1000-series 2-stroke needle.

So, is the 0.034"-longer needle from the 932 appropriate to use in my 1036? If not, what is the part number of the needle I should use?

p.s. In case it helps someone in the future, the present jetting that works in my 1036 2-stroke Concentric on a DBD with 65-2446 inlet and exhaust cams, 10:1 piston, 'twitter' silencer but no air filter is:

25 pilot
.107 needle
2-stroke rich needle (1 groove, 2.297" long) on middle notch
2-stroke spray tube
#3 cutaway
290 main jet

p.p.s. Before someone tells me I should get a Mikuni, I have two 38 mm Mikunis (and a 1038 Amal) on the shelf. So, you don't need to tell me to get a Mikuni (you could tell me I'm a fool for not using one, but you needn't bother telling me to get one...).

Addendum:

I used a piece of 5/16" Al rod to make the tool shown in the fourth photograph to press the spray tube out of a donor 900-series Concentric. The end that fits into the tube is 0.243"-dia. and the section that fits through the carburetor as it pushes the tube out is 0.309"-dia. The smooth portion of the tube is a slip fit in the body with the knurled end the portion that secures it in place.

I'm a little puzzled because I measured the knurled end to be 0.372" which means the hole into which it was pressed must have started life a few thou. smaller than 3/8". Typically, holes are made with tooling that has the nominal diameter while the shafts that go into them are appropriately under or over-sized.

Anyway, the knurls in the carburetor can be seen from the fifth photograph. The top of the jet holder doesn't reach nearly as far as the bottom of the spray tube so I'll have to count on the same knurls in the 1036, plus Loctite for good luck, holding the replacement spray tube in place.



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Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/14/19 12:07 am

http://amalcarb.co.uk/mk-i-concentric-series/1000-series/needles.html


Taken off Amals page for 1000 series spares, the 4 stroke V needle has the same part number as the 900 series, the two stroke needle and alchohol needle have 1034 start numbers and are not listed in the 900 series parts.
Guessing here, but possibly the needle seat in the slide is the same height as the 900 series, Ive never seen a 1000 carb, and the other two one off needles are special tapers?
In the UK Surrey cycles know more about Amal carbs than pretty much anyone else, try emailing or calling them, they are very helpful over the phone.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/14/19 1:26 am

Originally Posted by gavin eisler
Guessing here, but possibly the needle seat in the slide is the same height as the 900 series,
Good call. Your post sent me back to the garage to check, and indeed they are the same height, as is shown in the first two photographs (it's not easy to tell from the second photograph, but the top of the seat in both is the same height above the base of the slide).

However, as the third photograph shows, the projection for the jet holder on the 1036 (on the right) is ~0.050" shorter than on the 932.[*] This physically raises the needle jet by that amount which has the same effect as dropping the needle by almost 1 notch (0.063"). Perhaps this is all within the overall scheme of things due to differences in air flow when chokes get massive.

Given that the Amal site shows different 2-stroke needles, but the same 4-stroke needle, as for the 900 series, I was worried that might be a mistake on their site. Thanks to your suggestion, I'm now less worried. However, I'd still like to hear from people whose 4-strokerized 1036 (or 1038) works well and who knows for sure what needle is in it.

[*]A more careful measurement found ~0.035", which is equivalent to only ~1/2 notch of the needle. I also checked a 600-series and found it to be identical to the 900.

p.s. In light of this latest revelation I see now that the same 4-stroke needle is used in 600, 900 and 1000-series Concentrics, although the 2-stroke needles differ for each. I had not realized this before. Although I have a Concentric on my BB Gold Star, because that's how it came to me, I grew up in a pre-Concentric world. Oh, also on my Trident, but that's an anomaly in my world.

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Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 03/14/19 5:24 am

Interesting, and asks questions I've long held too, regarding the 2 to 4 stroke changes required. I'd done all the research years ago, but never actually got to changing the spray tube, etc.

Unfortunately, my bike that had a 1038 on it, as a road-racer, is long gone, but I might be able to get the current owner to provide some data. It might take some time though..he doesn't visit his computer much!

One thing I am confident about - the spray tube won't escape down the inlet if it does come loose..
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 03/14/19 11:54 am

MM,

My DB is similar to your specs, but 9-1 instead of 10-1 and I run an air cleaner.

I am not going to go off memory, but let me see what I have written down for the jetting with a 1038 converted to a 4 stroke carb. I am still a little off with the slide cutaway (rich) but that has not been enough of an irritant to make it better.

I tried a 1036 that was converted to 4 stroke but the bike just never seemed to run right. A 1038 made all the difference in the world.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/14/19 7:39 pm

Originally Posted by Rich B
I tried a 1036 that was converted to 4 stroke but the bike just never seemed to run right. A 1038 made all the difference in the world.
Although there aren't many 1036/1038 Gold Star specs to be found, those on Britbike span a pretty wide range:

pilot jet 25, 30 or 35
slide 3, 3.5 or 4
needle jet .108
main jet 300 - 390

Unfortunately, it isn't always clear whether some of these results are based on personal experience, or just repeating results posted by others. So, I feel I'm in largely uncharted seas, like those of the first photograph.

In addition to the above jets, the configuration of spray tubes required to make engines happy also ranges widely, as shown along with the direction of air flow in the second photograph. Note that the angle of the slash cut in the Trident/Rocket3's spray tube is steeper than that of a 2-stroke, although it only covers half the diameter, while the cut in the Norton's is even more radical. For the Trident/Rocket3 a relatively small 27 mm carburetor feeds a 247 cc cylinder, while for the Norton a larger 32 mm carburetor feeds a 414 cc cylinder so the effect of spray tube geometry covers a wide range of cylinder and carburetor sizes. The only thing I've found is one unconfirmed report that a non-notched spray tube in a Norton causes a mid-range flat spot. Typically "flat spot" would mean a lean mixture, but it could be rich depending on who is (mis)diagnosing the condition.

Anyway, with the above in mind, plus the aggressive cam overlap of a Gold Star that causes fuel to pass across the spray tube more than once, and given my present state of ignorance[*], it's not at all obvious to me that a 2-stroke spray tube for my engine would be "bad" while a generic flat-top 4-stroke would be "good."

[*]Joseph Heller nicely sums up my knowledge of spray tubes with this quote from Catch 22: "Come to us with a liver complaint and you can fool us for weeks. The liver, you see, is a large ugly mystery to us. If you've ever eaten liver you know what I mean. We're pretty sure today that the liver exists, and we have a fairly good idea of what it does whenever it's doing what it's supposed to be doing. Beyond that we're really in the dark"

The inlet port of my DBD head measures 36.80 mm (1.449"). In addition there's a phenolic spacer that's slightly larger at 37.2 mm. Since I have both a 1036 (whose outlet measures 36.0 mm) and a 1038 (38.0 mm) I tried them on for size. One thing to note is the holes in the flanges are slightly larger than the OD of the studs so there's a measured up/down free play of 0.010". That said, normally someone would tighten the nuts while the carburetor hung in the low position rather than try to center it on the studs so it would sit ~0.005" lower than the centerline of the studs.

The third photograph shows the step when the 1038 bolted directly to the head, without the phenolic spacer. Such steps can be caused by undersized gaskets and often cause problems with idle and low speed running because the fuel from the pilot circuit hugs the bottom of the tract for quiet a distance.

I'm not bothering to include a photograph of the 1036 without the spacer because the ~0.4 mm step down from the carburetor to the larger inlet can't easily be seen in an iPhone photograph with poor lighting. However, the fourth photograph shows the 1036 with the slightly larger diameter phenolic spacer in place, where the tract goes from 36 mm to 37.2 mm and back to 36.8 mm. For the 1038 this would be 38>37.2>36.8, which might seem to be better because it is a "smooth" progression, but air flow doesn't live by such simple arithmetic so there's no way of knowing without actually testing it.

Just for interest, the fifth photograph shows the 1038 sitting on the 1036 with the 1036's flange blued to make it more visible.

The Plan: What I'm thinking as of now, subject to changing my mind, is to change the jet holder and needle of the 1036 to 4-stroke versions but leave the 2-stroke spray tube in place. Then, I'll see if I can sort out the jetting to give good performance throughout the range. If I can't, I'll replace the spray tube and see what difference it makes. Assuming I eventually succeed in getting the 1036 working well, I'll then apply the identical configuration to the 1038, swap carburetor bodies, and make whatever tweaks are needed to it to optimize its performance. Because of the Catalina's air cleaner and Monobloc screw top it's quite an ordeal to swap carburetors on it, but it's much easier with the Concentric on the Competition. Unless some unforeseen obligation arises, optimistically I hope to have the jetting sorted out by sundown on Sunday. Whatever I find with my 1036/1038 experiments should be of interest to more than just me.



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Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 03/14/19 10:24 pm

Originally Posted by Magnetoman
The Plan: What I'm thinking as of now, subject to changing my mind, is to change the jet holder and needle of the 1036 to 4-stroke versions but leave the 2-stroke spray tube in place. Then, I'll see if I can sort out the jetting to give good performance throughout the range. If I can't, I'll replace the spray tube and see what difference it makes. Assuming I eventually succeed in getting the 1036 working well, I'll then apply the identical configuration to the 1038, swap carburetor bodies, and make whatever tweaks are needed to it to optimize its performance. Because of the Catalina's air cleaner and Monobloc screw top it's quite an ordeal to swap carburetors on it, but it's much easier with the Concentric on the Competition. Unless some unforeseen obligation arises, optimistically I hope to have the jetting sorted out by sundown on Sunday. Whatever I find with my 1036/1038 experiments should be of interest to more than just me.

I think you need to replace the needle jet as well. The bleed hole makes a difference
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/14/19 10:50 pm

Originally Posted by Shane in Oz
I think you need to replace the needle jet as well. The bleed hole makes a difference
Right you are. I showed the holy jet in an earlier post.

Update: my hoped-for Sunday completion date may have slipped through my fingers. I have ~20 4-stroke Concentric needle jets from .105 to .113, but I just found that none of them are the .108 that some people have said is needed (a .106 that I previously misread made me think I had a .108). I've now ordered two of them but based on the fact most bikes take a .106, including the B50MX, I'm a bit skeptical something as large as a .108 is needed. While waiting for the .108s to arrive I'll try a .107.
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 03/14/19 11:53 pm

It is a miracle, I remembered to look in my notebook.

And there is a break in the AFT race from Daytona.....so here it goes

Pilot jet - 30
Slide - 3
Needle - 4 stroke 2 rings, top groove
Needle jet - 107 4 stroke
Main jet - 340
Spray bar - STD. 4 stroke.
K&N air filter

IMO I am a bit rich on the slide, but the mid range/top end gives a great plug reading. The bike starts easy, takes throttle well, so having a hard time convincing myself to make it better. Mid range is amazing.

I live about 900’ elevation, typical east central Ohio weather.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/15/19 12:04 am

"optimistically I hope to have the jetting sorted out by sundown on Sunday." Good one MM, I note you didnt say which Sunday, stay optimistic. At least its half the work of a twin, but you have a few variables to deal with.
I recall helping a friend out with twin 32 Miks off a 500 twin Suzuki 2T fitted to a hotted up A10, these were the hot ticket, even with the slides in backwards " You cant get them wrong , they are polarised" says he, " Aye ye can" I said, and he did. Even then the bike ran , obviously wrong , but it ran, did 4 mpg. Improved a lot with the slides fitted correctly enough improvement to run well enough , its all relative.He spent some more time fiddling with the main jet and that was it, then the crank broke. My point is . probably most folk fitting new/ big/ different carbs pay scant heed to the finer points, so long as it runs, might have a flat spot, might need constant blipping but it runs, I doubt if many have the time / skills or inclination to get much further than that, too much uncharted territory and miss understanding. Best of luck with your trials, only guessing here , but going from 2st to 4 T spray tube, I imagine you may need a richer slide or different richer needle position to compensate, this is pure conjecture , probably wrong, . Do the reverse . As I understand it the cutaway has an en richening effect, removing it should need some other type of compensation, its probably too rich as is, you might not need to , who knows?

Moving the needle jet up a wee bit in the 1000 probably keeps it proportionally in the same position as the 900 as a ratio from centre to jet compared with choke OD. If it was me I would fit the 38 and copy Rich Bs settings when he posts them, just to have a known baseline. have you got Lambda sensor gear to help you out? I am very jealous of that stuff, my seat of the pants, choke lever tests are just one step above guesswork, numbers would be cool. I dont know if this is a fair comparison, but my 732 has two 30 mm carbs same as the 650 same cams same pipes, bigger valves, compared with 650 carb setting I am lower numbers MJ, NJ and needle. Extrapolating wildly from this one sample , fitting a 36 in place of a 38 to a 500 will give similar effects, higher gas speeds in the smaller carb mean smaller jets etc compared to a lower gas speed/ bigger carb. Taking a stab at it with some schoolboy maths , 36 mm choke area 1018.mm Sq, 38 mm choke area 1134, percentage difference 116 /1134 x 100/1 = 10% of 38 . This reduction factor could be applied to rich bs settings as a crude start point for the 36. Again, almost guess work , but its a start point.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/15/19 12:06 am

Originally Posted by Rich B
I remembered to look in my notebook.
Being a life-long keeper of notebooks, often my problem is remembering which notebook to look in.

This is great information. Thanks very much. Since my engine now has a K&N filter on it I'll start out with your settings, except for keeping the 2-stroke spray tube for now. I wonder if the richness you have will result in me ending up with a .106 needle jet. We'll see.

Again, thanks very much.

Originally Posted by gavin eisler
have you got Lambda sensor stuff to help you out?
Indeed I do. However, it helps a lot to get close before deploying advanced technology. When the Catalina returned from our Texas ride 18 months ago it ran OK-ish, but the tale of how I found the needle jet had worn out, the fuel level was 1/2" too low, and the replacement silencer was sending a very rich cloud back through the carburetor to screw jetting up only when the air filter was attached can be found here. Only after locating and sorting out issues like that is it time to capture a stream of data to five significant figures.

Originally Posted by Rich B
Just to be clear, the bit rich spot is very low throttle settings when the slide is primary control.
That's very helpful. I pay particular attention to whether I need to machine a larger cutaway in the slide.
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 03/15/19 12:29 am

YW

Just to be clear, the bit rich spot is very low throttle settings when the slide is primary control. Once on the needle/needle jet, I am very happy with the plug reading and response.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 03/15/19 6:03 am

Standing by with interest in the results.

MM, can you use your uber-accurate measuring kit to find a worn .107 in lieu of a fresh .108?
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 03/15/19 12:06 pm

As a reference on Concentric needles, I give you this. It is not an original, I plagiarized this from a John Healy post something like 11 years ago. So thanks John!

Amal Concentric Needles

Amal supplied 5 needles for that MKI Concentric. they are identified by thin annular grooves above the three needle clip grooves.

1 ring is rich two stroke approx. 2.290" long
3 rings is lean two stroke approx. 2.485" long
2 rings is standard 4 stroke approx. 2.677" long
4 rings is Norton 850 approx 2.765" long
5 rings is T160 approx 2.735" long

This is from my own info....

Spanish made 2 stroke needles may also have a letter stamped on the needle indicating rich or lean 2 stroke. Since it is in my notes that are not handy, X & U runs in my mind as the letter. If I am wrong, I will correct that.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/15/19 4:50 pm

Originally Posted by Kerry W
can you use your uber-accurate measuring kit to find a worn .107 in lieu of a fresh .108?
I have my doubts whether a .108 is going to be needed, supported by Rich B's jetting data where he has a .107. But, as soon as I discovered my "108" actually is a .106 I measured all the .107s hoping to find a large one, just in case. All were within spec. However, although I don't think I'll need them, I still ordered a pair of .108 to have on hand.

Originally Posted by Rich B
As a reference on Concentric needles, ...
I have a printout of John's tuning information with part numbers for various needles in the form of a ~20-page document titled "Beyond the Basics." It is chock full of very useful information but doesn't touch on the 1000-series Amals, probably since none were used on British motorcycles, only on Spanish 2-strokes.

Amal's current web site shows the same 2-groove, 622/124 standard 4-stroke needle was used for 600, 900 and 1000-series bodies, but different 2-stroke needles for each. They still list a 4-groove for Norton (with a 928/104 part number consistent with having been introduced with the 900-series carburetor used on a Norton 850), but the 5-groove is listed as "4-stroke emission" (622/278, consistent with the 600-series used on a Trident). The 2-stroke needle for the 1000-series is termed needle 'O" (1034/063), which is what is stamped on the needle I removed from one of my carburetors.

Having learned from replies in this thread that the same standard 4-stroke needle is listed for all three series, plus having the dimensions in John's booklet, gives the possibility of an additional level of fine tuning. For example, the 5-ring "T-160" needle is 0.058" longer than the standard, with a gentler taper that begins 0.024" sooner. So, if otherwise everything else is good, but the mixture gets too rich too fast as the needle is withdrawn, switching to a T-160 needle could address that. Referring to Gavin's earlier post, it's after the basic jetting has been figured out that my digital air/fuel system will come into its own to tweak the jetting into being as good as it possibly can be. Until the carburetor starts to wear...

Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 03/15/19 11:14 pm

Good thing I didn’t go off memory for Spanish 2 stroke needle....

U - std 900 series 2 stroke 57.93mm/2.28” long
X - rich 900 series 2 stroke (the only one I have is in a carb on a bike)
X-1 richer 900 series 2 stroke (I don,t have one)
O - std. 1000 series 2 stroke 66.86mm/2.63” long
O-A - rich 1000 series 2 stroke (none to measure)

Good thing this subject came up......forced me to look at Spanish Amal info. I need to find some 1000 needles.....building 2 Bultaco vintage flat track bikes is gonna require spares.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 03/16/19 4:00 am

MM...contrary to the above, 1000 series (1036) Amals were used on very late Velo Thruxtons. (incidentally, with a 30 pilot, .106 nozzle, 320 main and a 3 slide - no mention of the needle variant - assumes standard - with clip in the top groove, and the use of the '1034/70 air tube'. In another veto book there is mention of a 1036 on a Thruxton, with a 'slash cut' spray tube, 30/320/.106 setup, though with a 2.5 slide and the needle clip in the 2nd groove and 70mm intake trumpet).

Also, as a minor aside, one reference to stock 1036's on the Velo notes the use of the 622/056 'alcohol' float bowl, with the 4mm/0.156 feed hole.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/16/19 5:00 am

Originally Posted by Kerry W
(1036) Amals were used on very late Velo Thruxtons. (incidentally, with a 30 pilot, .106 nozzle, 320 main and a 3 slide - ... with clip in the top groove, and the use of the '1034/70 air tube'. In another veto book there is mention of a 1036 on a Thruxton, with a 'slash cut' spray tube, 30/320/.106 setup, though with a 2.5 slide and the needle clip in the 2nd groove and 70mm intake trumpet).
That's all very helpful information. Thanks very much. I'd forgotten that Velocette survived past the Jurassic into the Concentric era.

It was one of those two steps forward, one step back, and repeat, kind of days. But, the Gold Star started on the 3rd kick and I made two laps of the driveway so it wasn't a bad day at all.

I needed to put an Ewarts-type right-angle push/pull petcock on the right side because of limited clearance over the carburetor, but using cork for a seal was a little too 19th Century for my sensibilities. I was planning to machine my own O-ring plunger when last week someone on the Ariel Owners Club forum mentioned that Baxter Cycle carried them. I started to order one plus a spare (at $20 ea.) but the order form showed that shipping was free if I ordered $50 worth of merchandise so I ordered three to save the $8.50. Depending on how you look at it I either got the third one for $11.50, or I paid $60 for the one I'm actually using.

For reasons of expediency one petcock has an outlet tube that's 1/4" OD while the other is 5/16". I machined a brass adapter for a Cu 'T' to give it 1/4" and 5/16" inlets and a 1/4" outlet to connect to the carburetor.

I then rebuilt the 1036 using Rich B's settings for his 1038 (30/340/.107/#3/top groove), except leaving the 2-stroke spray tube in place. After installing it I lowered the lift, wheeled the bike out to the carport, and decided to try to start it the old fashioned way. It started on the 3rd kick and I made two laps of the driveway before stopping to adjust the throttle stop (yes, I know it wasn't warmed up yet). It's a left hand carburetor and while balancing the bike to try to do this it died. It didn't start after a couple of kicks so I put it up on the DocZ rollers. The photograph shows how I modified the rollers with a removable cross bar that I can use to strap the bike in place, which is quite handy at times like this.

The rollers didn't have the h.p. to turn the engine over so that, plus a glowing terminal on a relay, told me one of the two starter relays was fried. When I initially installed the second motor I ran both off the same relay a few times before installing a second one, which I shouldn't have done. Anyway, this setback sent me to the local Autozone for a replacement. I rolled the DocZ back to the garage to put on the lift to install it, then rolled it back to the carport. The rollers worked for about 3 sec. and died abruptly. Thanks to my superior electrical skills I was able to diagnose the problem. The electrical connector at one of the battery clamps had broken in two separating the cable from the battery. So I then fabricated a new connector from a sheet of Cu and crimped it on the cable.

With the DocZ back in action the Gold Star started. But, the sun was about to go down and the temperature had dropped below 70oF into the frigid 60s so that ended the day.


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Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/17/19 12:45 am

Another day is done, and at the present rate of progress my Competition Gold Star may never run. Sigh...

Today the DocZ just didn't have the h.p. to spin the engine over more than a few revolutions before running out of steam. Since yesterday I had installed a new solenoid I suspected one of the motors wasn't getting power so I connected two clamp-on ammeters to the leads. They showed that both motors were getting power, but that the current in each dropped from ~200 A to ~100 A within ~5 seconds. So, I tested the battery (which was four years old) using a tester that draws ~100 A and it showed up as "weak."

I put the battery in the car and drove off to buy a replacement. There was a $12 core credit, but the guy at the store insisted he had to test my battery to see if it was any good before he could issue the credit against the new battery, and the test would take 15 min. I said my battery was bad, I wasn't returning it under warranty, I just wanted the credit and to be on my way. Since clearly I was an idiot for not understanding, he slowly explained to me that it was store policy. I asked him to call the manager but before they showed up the battery failed the test and I got the credit.

Once back in the carport I hooked up the battery and it spun great. Except the tire wasn't turning. As shown in the first photograph I found one of the rollers had shed its abrasive covering (nb. DocZ now sells rollers with a laser cut pattern in them rather than using abrasive paper). I have abrasive paper in all sorts of grades, but only small amounts of coarse abrasive cloth so off to the Ace Hardware. I found they have 10,000 (estimated) varieties of sandpaper but, after a lot of looking, only one package of abrasive cloth, containing an assortment of three grades.

Back home I found my 1 gal. container of Barge Cement was less than fully liquid. If it's not one thing, it's another. Sigh... The solvents it uses (e.g. toluene) aren't anything I care to use for anything so I had nothing to use as a thinner. Still, it was liquid-y enough to (barely) use so I smeared it on the roller and on the back of 50-grit cloth, waiting the necessary five min., and attached it as shown in the second photograph.

After the cement dried I put the Competition on the DocZ, which then almost instantly shredded the cloth as shown in the third photograph. The glue seemed to be fine, it was the cloth that wasn't up to the task. The bike tends to climb onto the back roller so that one gets most of the wear. Although the abrasive on the front roller is still OK, swapping rollers isn't an option.

I am very interested in suggestions for what abrasive material I can attach to the roller that won't disintegrate so I can get back to jetting the bike.


Attached picture Roller01.jpg
Attached picture Roller02.jpg
Attached picture Roller03.jpg
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 03/17/19 9:18 pm

Originally Posted by Magnetoman
Since clearly I was an idiot for not understanding, he slowly explained to me that it was store policy.


I am afraid it is a symptom of the modern age. Store assistants seem to be incapable of independent thought and have been told to keep to The Script. because the rest of us are, as you say, idiots.

I went to a large car parts store a while ago and asked for some EP80/90 gear oil (it was for a van). The young guy behind the counter asked me for the vehicle registration number and I repeated I just wanted the said oil. He said that he needed the number so I obliged. After a minute of tapping at his keyboard he informed me that they didn't stock any oil for that vehicle. I told him that I couldn't believe that they didn't stock EP80/9 gear oil and at that point another guy came to the counter from the warehouse behind and heard me asking the last question. The new guy then said that they had loads of it in the warehouse. WTF!

Sorry for going off on a tangent.

Back on topic, what about using some of that stuff that gets used to put anti slip coatings on things like steps? My initial thought is that boats may use something so try a chandlers? Or a building supply place if they use it on metal steps?

Also, what about asking DocZ what they used?

John

Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/18/19 12:01 am

Rubber,maybe? dunno about gluing it on, the steel roller isnt helping, neither is the tight radius , the sort of stuff they make sander belts out of is pretty sturdy. Wind it on barbers pole style with a decent contact cement. Thats how drum sanders are made. usually on a bigger ( plywood laminated disc ) drum though.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/18/19 1:58 am

Originally Posted by George Kaplan
what about using some of that stuff that gets used to put anti slip coatings on things like steps?
Also, what about asking DocZ what they used?
Originally Posted by gavin eisler
Rubber,maybe... the sort of stuff they make sander belts out of is pretty sturdy. with a decent contact cement.
Anti-slip paint is a good suggestion that sent me to McMaster-Carr. There I came across anti-slip tape that looks like it might be the stuff DocZ used originally. I emailed him yesterday but for now I'll assume he doesn't check email on the weekend but will promptly reply tomorrow...

The not-fully-liquid contact cement I used may well have contributed to yesterday's failure (solvent for it is on order). That, plus not removing all the old material before gluing on the new. This left voids under the new material which easily could have cracked resulting in rapid disintegration. If it wasn't such an effort to disassemble the DocZ then placing the roller in the lathe to remove the old material (and maybe knurl the roller?) would be easy. I'll have to see how difficult it is to scrape clean in situ once I hear back from DocZ. I don't want to do anything until then (because it will be a messy job and I'm waiting to hear from him as an excuse to procrastinate).

The torque of my 10:1 Competition is causing issues with the DocZ that none of my lesser machines have ever experienced. I tried once with my leg today but the backfire reminded me why I got the rollers in the first place, i.e. to save my leg for another day.

The problem with turning over this high compression engine is due to a combination of electrical losses and friction. Addressing electrical first, the new battery I bought yesterday is for marine use so it has screw terminals that I can use to make the best possible low resistance contacts to it. The jumper cables supplied with the DocZ are 4 AWG which a calculator shows have a 6% voltage drop when powering both motors under full load. That the present cables are undersized can be felt in the heat generated in the wires. Anyway, this loss is too much so I ordered 1/0 AWG cables to replace them (which will reduce the drop to 2.4%). When it arrives I'll make my own Cu connectors for both ends of the cables. I also modified the battery clamps I bought previously to replace the DocZ clamps, installing Cu pads to make contact with much greater surface area to give lower resistance. At the same time I made 1/8" x 1" Cu pads (equivalent in cross section to 3/0 wire) that bolt directly to the battery to which the clamps clamp. Even with the present 4 AWG cables this made a noticeable difference in the power delivered to the motors. Yes, a direct hard-wired connection would have the lowest resistance, but no way would I consider doing this on a portable setup. With clamps there's hope to knock one free in an emergency.

The new battery is rated 845 MCA, which means it can supply that much current for 30 sec. at 32 oF before the voltage drops below 7.2 V. However, since the current will drop proportionally, by the time the voltage drops that much the power to the motors will be reduced by (7.2/12)2 = 60%, i.e. to 40%. The power available in a battery goes up with temperature so 845 MCA is equivalent to ~940 A for temperatures in the range 65 oF<T<105 oF, a temperature range outside of which no sane person would even consider riding. The motors draw 480 A total under full load which says the battery should last 940/480 x 30 sec. =~60 sec. before falling below 7.2 V, i.e. for the power to be reduced to 40%. So, perhaps half this time, ~30 sec., can be expected from the DocZ before the motors are too weak and the battery has to be recharged. I haven't used a stopwatch, but this is roughly what I observed today in ~4-5 attempts to start the bike.

Drawing 480 A for 30 sec. is 4 A-hr. so it would take a 6 A charger 40 min. to restore full power after 30 sec. of full load operation. A 20 A charger would do this in 12 min. Since ~45 min. with my 6 A charger is what I actually observed today, and since that is a long time for an impatient person to wait when they want to ride their damned motorcycle, also on order is a 20 A charger, the largest recommended for use with a battery of the A-hr. rating of mine.

As for friction, my fingers are crossing hoping Mr. DocZ gets back to me tomorrow with the answer to my question about friction material. Even with the present power losses on the DocZ, the Competition's wheel comes to a stop when I let out the compression release after which the bare Al roller just spins against the stationary tire.

So, to summarize everything written above, the jetting work is no further along than it was yesterday at this time. Sigh...
Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 03/18/19 3:31 am

Originally Posted by Magnetoman
Yes, a direct hard-wired connection would have the lowest resistance, but no way would I consider doing this on a portable setup. With clamps there's hope to knock one free in an emergency.
Have you considered adding a mechanical battery isolator to the circuit? These are often used for marine applications, four wheel drives and big trucks. It will add some resistance, but they are quicker and easier than trying to knock a melting terminal off a battery pole.
A heavy duty solenoid might be an option as well.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/18/19 3:51 am

Originally Posted by Shane in Oz
Have you considered adding a mechanical battery isolator to the circuit?
Hmm. I suppose I could have a big red 'disaster' switch hooked to a~500 A relay. But, I'd have to give some thought to the step of making the initial connection to the battery. With clamps there's the possibility for an immediate disconnect but with a separate switch there would be a delay getting to it.
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 03/18/19 6:50 am

We used to start the booze drinker with a soft plug that was not done up tight, thus lowering the compression a bit.
Once warmed it started quite ( well relatively anyway ) easily.
From cold it would take 3 of us to push then 2 needed to jump on board or the back wheel would just lock up & slide.
Once warm, it would start with little more than its own weight.

Is there enough down force on the rollers ?

Agree with Shane on the solenoid.
Plenty of remote car starting solenoids around that will take 3 minutes of cranking

As for the battery try a spiral wound cell one.
They have a larger plate surface area and more connections between the plate & the busbars.
Thus they can supply a lot more amps for longer than most square plate batteries.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/18/19 10:30 am

You could use the roller set up as its own lathe , just needs a temp tool post.
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 03/18/19 12:54 pm

Just seen a kid on a skateboard which had an anti-slip coating on it. It looked exactly like the stuff you need

John.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/18/19 4:05 pm

Originally Posted by BSA_WM20
Is there enough down force on the rollers ?
No, but the only solution to that is for me to gain weight or fill my pockets with Pb.
Originally Posted by BSA_WM20
Plenty of remote car starting solenoids around that will take 3 minutes of cranking
The, ahem, current situation is unusual in that these are starting rollers, not continuous-running rollers. They are designed to start bikes that already are in running condition so, as such, they only need to turn the engine over a few times to get it to start. A bike that doesn't start after 5 sec. of having the rollers actually spin the tire is telling the owner that it needs remedial work on the electrical or carburetion system. Spinning it for 3 min. would just be a waste of perfectly good electrons. I assume/hope that with a proper friction surface on the rollers my present weight will suffice, as it does when starting other bikes.[*]

[*]What I don't remember happening with my other bikes, although I'm not 100% sure, is despite the front brake being on the rear roller pulls the 10:1 Competition back an inch or so, taking it off the front roller (which still has abrasive) and lifting it onto the now-bare rear roller. Because of this the friction available to spin the tire has been reduced by well over 50% while at the same time the torque needed to turn over the 10:1 engine is greater than with my lesser machines (which is why it was pulled back onto the rear roller in the first place).

Originally Posted by BSA_WM20
As for the battery try a spiral wound cell one.
If a battery with a different internal construction provided the same number of MCA or CCA in a smaller size it wouldn't matter for me. All that matters is that a battery can supply enough VxI to the DocZ's motors to overcome the reluctance of a 500 cc, 10:1 piston to make it past TDC a half-dozen or so times. It can supply the necessary power now despite the losses in heating resistive connections, but it will do it even better after new cables and connectors are in place.

Originally Posted by gavin eisler
You could use the roller set up as its own lathe
Originally Posted by George Kaplan
a skateboard which had an anti-slip coating on it
An email from Art 'Doc' Zimmerman was waiting for me when I woke up this morning asking me to call to discuss the solution. I got his voicemail asking me to leave my number so am awaiting his return call. Stay tuned for developments on the friction front.

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/18/19 11:13 pm

I had a great, wide-ranging, hour-long discussion with Art 'Doc' Zimmerman today, including about my DocZ rollers. Relevant for my present needs are that his use of 3M Safety Walk abrasive pads on the rollers identifies mine as one of fairly early production after he started in 2002. He makes a "speedway roller bar" that bolts on the back of the unit to press against the tire to keep 14:1 speedway bikes from being pulled backwards onto the rear roller, as is happening with mine. So, as soon as our conversation was over I headed to the post office to send him a check for one (he doesn't take credit cards or Paypal -- luckily, my wife is one of the last people in the world who still uses checks).

Thanks to our conversation I have a short-term and a long-term plan for my DocZ. Short term, tomorrow I'll be getting "Extreme Traction Anti-Slip Tape" from McMaster-Carr that I ordered yesterday on speculation. 'Doc' told me that when he used tape he would clean the rollers and apply the "3M Safety Walk" tape, then spray lacquer as a protectant. I'm not sure the lacquer will do any good, but I'm not going to alter the recipe. If the tape I'll be getting works as well as the original 3M it will solve my short-term problem (once the roller bar arrives). Longer term I'll buy a set of his new improved "forever" rollers and after I get around to installing them will send my current ones back and he'll send me the $30 ea. that he otherwise would have knocked off the $60 ea. price in a normal exchange. Doing it this way will minimize my down time.

I also learned from him that each motor puts out 3.5 h.p. at 12 V (which I already knew from my own measurements), but that they can be operated at 18 V without problem to give 4.5 h.p. He said doing this is common practice with speedway riders. Further, as long as they are only operated under load and not allowed to spin free, they can be operated at 24 V to give 8 h.p. ea. I may just buy a second battery, flip the DocZ upside down, and ride it instead of the Gold Star. Anyway, if the 10:1 is too much for the 7 h.p. I presently have I now know I have the option of adding a 6 V battery in series.

He said on average he counts on it taking 6 sec. for the rollers to start a bike, and that 3rd gear is the one to use. He recommends using a deep cycle marine battery, which is what I bought this weekend, because it recovers nearly fully within a few hours. Still, I'm happy I ordered a 20 A charger because who has the patience to wait a couple of hours?

The first photograph shows the condition of the rear roller as of earlier this afternoon, and the second photograph shows it ~45 min. later. It took maybe 15 min. of physical labor with the knife, pliers and razor to get most of the residue off, 5 min. to move the rollers into the garage and gather the air tools, and 10 or 15 min. with the Scotchbrite pad and fine abrasive disk, followed by acetone, to get it surgically clean and ready for tomorrow's arrival of the anti-slip tape. It would have taken a lot longer, and without doing as good a job, without air tools.

If I work up the courage to ask my wife to stand behind the bike and help keep it from moving I'll try to start the bike after applying the anti-slip tape. No, no, scratch that foolish idea. It will be much safer to be patient until the roller bar arrives.


Attached picture Roller03.jpg
Attached picture Roller04.jpg
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 03/19/19 6:17 am

Quote
He said on average he counts on it taking 6 sec. for the rollers to start a bike, and that 3rd gear is the one to use. He recommends using a deep cycle marine battery, which is what I bought this weekend, because it recovers nearly fully within a few hours. Still, I'm happy I ordered a 20 A charger because who has the patience to wait a couple of hours?


This is why I suggested the spiral cell batteries.
I bought the first when the battery & alternator on the roller died during a wedding.
Jump started from the 2nd car then hot footed to the nearest auto electricians.
All he had in the size that fitted was the Optima spiral cell.
Not cheap but completed the hiring and never let us down.
I used to start all of the cars off the one battery & the RR starter motor would crank a diesel loco .
So that was 5 cold starts on 6.5l engines that had been standing for a month in the paddock and I could do that a dozen times before the battery needed recharging.
The rollers have the battery in the boot so there is a very long pair of battery cables between the battery & the starter.
And the starters are not geared so they pull really big amps.

Quote
If a battery with a different internal construction provided the same number of MCA or CCA in a smaller size it wouldn't matter for me. All that matters is that a battery can supply enough VxI to the DocZ's motors to overcome the reluctance of a 500 cc, 10:1 piston to make it past TDC a half-dozen or so times. It can supply the necessary power now despite the losses in heating resistive connections, but it will do it even better after new cables and connectors are in place.


I assume the Optimas we get down here are the same as the ones you get there as it appears they are made in Mexico
Note the current ratings for the marine batteries a reasonable bit bigger , not just the same thing is a different sized box.

Optima power ratings
Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 03/19/19 12:25 pm


To all mystified Yanks:

The post, above, written in Australian English, refers to a 'roller', or 'rollers'. These are emphatically not the rollers on MM's Doc Z. No, the roller in question is, I suspect, a Rolls Royce limo, favored in weddings and events in Britain and the (former) colonies.

Thus the batteries required to crank older Australian Rolls Royce limos had to be as strong as a kangaroo's kick.

Just thought I would clarify the lingo in case readers were scratching their heads, as I was.

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/19/19 4:32 pm

Originally Posted by NYBSAGUY
To all mystified Yanks:
Ah, the fog has lifted! Once I realized Trevor couldn't be referring to starter rollers I decided 'roller' must be Australian slang for 'car' (i.e. any car, irrespective of brand). Although that only sort of made sense, the actual point of his post was a comparison of batteries so I didn't try for a better translation. Much like my approach to speaking French (or German or Spanish), where sometimes I can get a roughly-appropriate noun and present-tense verb into something like a sentence so I count myself as "functionally fluent."

Returning from the outback to batteries:
Originally Posted by BSA_WM20
The rollers have the battery in the boot
OK, that gives the possibility of having a huge battery. For a direct comparison where space is a constraint I went to the Autozone web site (a large chain of auto parts stores), entered the details of my Ford F350, and got a list of 11 batteries that are supposed to fit. "Normal" batteries ranged from 650 to 850 CCA with a correlation between price and capacity ($70 to $190). There also were four Optima batteries in the list, 2 ea. at 750 and 800 CCA ($225 to $275). That is, although much more expensive, an Optima battery wouldn't supply any more starter current to my Ford than a conventional battery.

Part of the price difference is due to Optimas being "maintenance free" AGM whereas the low end batteries at Autozone are simple lead-acid. Five minutes of "research" into this doesn't tell me how much of the rest of the price difference is due to advertising terms like Spiralcell Technology® and Pureflow Techology™, but a CCA is a CCA. Maybe even though they deliver the same number of Amps for 30 sec., perhaps an Optima would last forever and thus would be a better deal for that reason. Or maybe Trevor drank the Spiralcell® Kool-Aid. I don't know, but I do know that I already bought a replacement battery a few days ago and so for present purposes the issue is moot.

Originally Posted by BSA_WM20
Note the current ratings for the marine batteries a reasonable bit bigger
That's simply because battery capacity is lower as temperature drops and CCA ratings are at 0 oF while MCA at 32 oF. Different ratings make sense because Canadians still drive cars at 0 oF but not too many use their motor boats when the temperature of the lake drops below 32 oF.
Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 03/19/19 7:51 pm

For what it's worth, I use Optima D27M deep cycle/marine (blue top) batteries which are rated 800 CCA/66 AH for the tractors (the four wheeled variety), which are only started when I need to do work around the place.
The drive to work diesel Nissan Navara has a pair of starting (red top) batteries which replaced the original failing Century sealed lead acid batteries.
The tractor batteries are at least 8 years old, but the Nissan batteries are only about 4.


btw, Rolls Royces being called "Rollers" seems to come from Arthur Daly in the classic "Minder" TV series.
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 03/20/19 9:38 am

Sorry about the confusion.
As MM had wandered around the said same ex hire cars when he visited Shane a few years ago I assumed he would be on board.
Yes they are the ex-hire cars form a failed business.

It was just a suggestion as these batteries seem to crank out full power for a fair bit longer than standard square plated batteries due to increases plate surface area.
Thus you should be able to spend more time cranking before the voltage drops too far.
They also seem to take a higher rate of charge, most likely for the same reason.

Had assumed tthey would be proportionally cheaper in th USA as they only need to be trucked from Mexico and not shipped 1/2 round the world then pass through 4 lots of hands with appropriate mark ups before my hands touch them.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/20/19 11:15 pm

Originally Posted by BSA_WM20
As MM had wandered around the said same ex hire cars when he visited Shane a few years ago
The truth comes out. Even though I might have nodded knowingly many times, only about 25% of the "English" spoken in Australia is understandable.

Setting batteries on the shelf for now, the abrasive paper arrived and is now on the rear roller. The roller is a little over 7" wide so I bought a sheet of 6" x 24" (enough for both 3"-dia. rollers, although I'm only doing one for now) and a strip of 1" x 24". I cleaned the roller again with acetone about a half-dozen times until there was more no discoloration on the paper towels, cut the paper to size, and applied it.

The glue seems to be very strong so I'm optimistic it will work. I used hose clamps to maximize the bond strength, and since I'll wait for the rear roller to arrive before again trying to start the Competition I'll offset the hose clamps after a day to compress the areas that are currently missed.

I modified the two clamps to make connections to the battery with ~1 sq.in. Cu pads. The resistance of those connectors is now only 0.22 mΩ each. Although with 500 A through them the voltage drop at each clamp only will be 0.1 V that's still 55 W of heat. Presently each of the 2 AWG cables has 6x that much loss (1.36 mΩ), which will be reduced to 0.86 mΩ with the 1/0 AWG cables that arrived this afternoon. However, still the losses in both of the connectors and cables account for ~10% of the total power supplied by the battery. Such is the nature of high currents. However, before these upgrades to the circuit the losses were over 2x as much so only ~80% of the available power got to the motors with the rest helping to melt the polar icecaps. Finally, since the bike will sit for a week, I drained the float bowl.


Attached picture Roller05.jpg
Attached picture Rollers06.jpg
Posted By: JakeH

Re: Correct needle for 1000-series Concentrics? - 03/22/19 1:52 am

Magneto Man,

I am a little late to this, The 1000 series is my favorite for a rider! They make decent power, easy to tune and live with and look decent
I usually tune them on the Dyno, and most are pretty close with this jetting.

Stock bike, muffler
I change to the standard 4 stroke nozzle, and jet holder.
30 pilot
3 1/2 slide
106 Needle Jet
2 groove needle
240 -260 Main


Race bike, with straight thru open muffler, lots of head work and big cams

4 stroke parts
30 pilot
3 1/2 Slide
106
2 Groove
340


Both were tuned just a touch rich on the
Dyno.
Great carbs!!

Good luck
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 03/22/19 8:43 am

Go on...tell us what the bikes made at the rear wheel!
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/22/19 5:05 pm

Originally Posted by JakeH
I am a little late to this,
It's certainly better late than never.

Your settings will be very helpful. Thank you very much for posting them. It's interesting that you found all the settings, except the main jet, the same for both configurations.

While my Gold Star is waiting patiently for the rear roller add-on for the DocZ to arrive I'll switch to a .106 needle (with apologies to Rich B). However, I'll leave the 2-stroke tube in place for now as well as start out with the #3 slide that I have. I can shave off some metal to turn the slide into a #3.5 but I don't know what effect the 2-stroke tube will have on the mixture at lower throttle settings[*] where it will compete for attention with the slide. I'm still waiting to hear back from Burlen if it uses the same 928/107 spray tube as does the smaller body and, if not, the part no. of the correct one.

[*]further research indicates the 2-stroke tube may weaken the mixture at lower throttle settings compared with a flat-cut tube. If this is true, the richer #3 slide may somewhat compensate. Once I get the jetting so the mixture "feels" close to correct I'll use my Innovate air/fuel meter to make actual measurements.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/22/19 11:03 pm

it might be easier to walk away from the rollers, and fit a thicker head gasket, at 9 to one you might not need them then you can get on with making your bike rideable, OK it wont be so fast, it will last longer.

When you dipped out as the temperature fell from 70 to 60 F , my heart blead pish for ye. I am dodging sleet showers because I cant get the bike in without a working front.

Something about what Budha said "all possessions bring misery" seems to fit these rollers.

Your initial chart is very accurate. Loved the pirates, My ancestors were Mac Neills from Barra.
Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 03/22/19 11:54 pm

Originally Posted by gavin eisler
it might be easier to walk away from the rollers, and fit a thicker head gasket, at 9 to one
I don't think a thicker head gasket will work with a Gold Star.
The cylinder liner has a lip which the head clamps down onto. The amount of gasket crush is apparently quite critical, which is why BSA used multi-layer "peel off" head gaskets. Too little crush leaves the majority of the head surface unsupported so will try to warp when clamped, too much and there is open space above the lip of the sleeve which does bad things to the combustion chamber shape and also burns the Al gasket.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/23/19 12:51 am

Originally Posted by gavin eisler
it might be easier to walk away from the rollers, ...
"all possessions bring misery" seems to fit these rollers.
If I only had one bike, or if I were facing some imminent deadline with this one, or if I didn't have other projects competing for attention, it would be frustrating. Luckily, none of these is the case. The rollers have been great since I got them, but the 'Competition' pushed it past the limit in its present non-speedway configuration.

I like solving problems, and figuring out where gains are to be made has been an interesting exercise (a milliohm here and a milliohm there and before you know it you've found a lot of power). Plus, waiting for components to arrive gives me time to learn more about the intricacies of the 1000-series Amal. It all comes down to the fact that understanding at a fundamental level how something works is as important to me as actually getting it to work. Although, the latter definitely is important.

Originally Posted by gavin eisler
When you dipped out as the temperature fell from 70 to 60 F , my heart blead pish for ye.
You'll get your chance to gloat in a few months when the daytime temperatures here top 100 oF. That said, one couldn't ask for better riding weather than I have 8+ months of the year, with the rest still rideable with some discomfort (unless base is temporarily relocated to the nearby mountains, in which case even the summer months are perfect). While it is uncomfortable to ride in the lowlands during the summer, in most other places it isn't even possible for half the year (nb. as is well known, Canada's total riding season is four days at the end of July...).

Originally Posted by gavin eisler
Your initial chart is very accurate. Loved the pirates,
Not to drop names but when the Ruler of Sharjah showed me that map in one of his museums a year ago I said "So, your ancestors were pirates?" He chuckled and then explained where he had acquired the map.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/23/19 3:17 am

Well, it is not in his home tongue thats for sure.
I hope the rollers work out for you, or you work them out, soon come.
You can gloat away with your high temperatures, I know you have terrible stoor over there, weve all seen The Wizard of Oz back home, . No danger of that here , or sunburn.
Definitely hypothermia. Smug it up.
Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 03/23/19 12:51 pm


Here we go again. This time it's the Celts mystifying the Yanks with their Hiberno-English..

Stoor - you won't hear that word spoken in Sharjah, although you might feel its effects. Stoor is dust, kicked up by a storm. It's a Highland Gaelic word (or even, a Barra word, handed down by the MacNeils) You won't even hear it in Ulster.

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/23/19 4:43 pm

Originally Posted by NYBSAGUY
Here we go again. This time it's the Celts mystifying the Yanks with their Hiberno-English..
At first I thought it was Celtic for 'President', although that didn't make sense in the context of the post. After convincing Google that I really did want the translation of 'stoor', not 'store', it said it meant 'dust'. However, that didn't make sense, either, what with Scotland being a land of moss and 100% humidity. Apparently, though, the translation was correct, although why the Scots have their own word for something they only could have seen in foreign movies is a puzzle.

I may have told this story before, but on a train from London to Glasgow I was in line (oops, sorry, that's 'queue' for those in the British Isles) to get coffee in the restaurant car. For several minutes I stood next to a pair who I assume were speaking "English," because every once in a while I could recognize a word. But, I would have understood a lot more had they been Parisians speaking French rather than Scotsmen speaking "English." Now that I think about it, instead of the U.S. Army using Navajo code talkers in WWII, they could have used Scotsmen speaking French to each other and it would have been equally incomprehensible to the Japanese. [*]

[*]It's not just Scots where there's an issue. The original 'Mad Max' was dubbed into proper English (i.e. American) when released in the U.S., with the more egregious Australian slang translated as well.

Originally Posted by gavin eisler
I know you have terrible stoor over there, weve all seen The Wizard of Oz back home,
Storms strong enough to transport me to Kansas are fairly rare, although they're likely to become more common with global warming. On the bright side, that also may make Scotland more habitable, although Barra will be half the size.
Posted By: kommando

Re: Correct needle for 1000-series Concentrics? - 03/23/19 5:09 pm

Quote
On the bright side, that also may make Scotland more habitable


If it gets warmer then the midge season will be extended, more habitable then becomes less habitable.

Well at least the horizontal rain will be warmer.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/24/19 12:39 am

I finished the upgrades to the DocZ's electrical system so now await the arrival of the speedway rollers to have it ready (assuming the abrasive paper stays on). The resistance of a clamp is 0.12 mΩ, which means a loss of 24 W at each connector when 450 A are flowing. With the new cables and connectors the resistance from the battery to each solenoid is 0.34 mΩ which means the total loss in the upgraded portion of the electrical system is 128 W, i.e. ~2.5% of the power supplied by the battery. The present (original) cables from the solenoids to the motors roughly doubles this, plus the as- yet unmeasured resistance of the solenoids themselves. Anyway, with ~95% of the power now reaching the motors and much less heat generated at the terminals, I'm declaring Mission Accomplished.

Moving on to carburetion, I've spent some time reading about Concentrics, including the Mark 2, and examining the 1038 that's not on the bike. This brings me to an important question:

** What are the IDs of the 2.5 and 3.5 air jets for a Mark 2 Concentric? **

Amal makes the passages and jets in their carburetors to be too rich at low throttle settings, then leans them to the proper ~14:1 by means of one of the two air passages at the bottom of the inlet to the carburetor (the other feeds the pilot circuit). All the 4-stroke Mark 1 Concentric bodies in my box have an air passage of OD ~0.188" running from the from the inlet to the area around the needle jet. However, the passages in the 1038 and a 627 from my Bultaco Sherpa T run most of the way at the same ~0.188" but then step down to ~0.082" (on the 1038; I didn't measure the 627) before reaching the needle jet. This is seen in the third photograph. The effect of this constricted "air jet" on 2-stroke Concentrics is to supply less air to dilute the fuel and thus keep the mixture richer at low throttle settings.

Amal gives a table of approximate settings for Mark 2's used with 2-stroke and 4-stroke engines. Looking at the 2036 and 2038, the 2-stroke recommendations are a bigger main jet (400 vs 320), larger needle jet (.108 vs. .106) and a smaller (richer) air jet (2.5 vs. 3.5). The recommended needle position (3), pilot jet (25) and cutaway (3) are the same for both.

I'm tempted to believe the Mark 2's air jets are sized in mm since 2.5 mm= 0.098" and 3.5 mm = 0.138", which are close to the sizes of the passages in the Mark 1 (given that the bodies are quite different I wouldn't expect them to be identical). But, if possible, it would be nice to have confirmation of this before I start drilling. Along with drilling would be tapping, so I could insert brass air jets of my own making should that be necessary.


Attached picture Resistance_clamp.jpg
Attached picture Resistance_clampcable.jpg
Attached picture AirJet.jpg
Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 03/24/19 3:59 pm

We recently worked on a Gold Star that had a 1038 Amal Concentric on it. It was hard to start and the owner had let it sit for a good while. When we took it apart it had the two stroke needle,main jet holder and a two stroke needle jet that had been modified by machining off the top.
As anytime I see two stroke jets and jet holders in a Concentric MK1 we changed to the 622/124 needle, 106 needle jet and changed the jet holder. We do this often on early concentric carbs as they came with the what we now call two stroke jetting. I did not do anything with the air inlet for needle jet. I suggest you ride it with the 4 stroke jetting installed before drilling on carb.
It now runs okay but with the funky rear sets and kickstarter it is a pain to physically kick. It does start much easier than it has since the owner bought 20 years ago. Form over function on a cafe racer again.
We also remove the air bleed jets on most MK11 Amals we work on.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/24/19 5:55 pm

Originally Posted by RPM
I suggest you ride it with the 4 stroke jetting installed before drilling on carb.
We also remove the air bleed jets on most MK11 Amals we work on.
Proceeding very, very carefully before removing metal from something like a carburetor is good advice.

In no particular order, some points relevant to this discussion are:

-- relatively few people use 1000-series Amals on their Gold Stars or Thruxtons (or G80CSs) so relatively few people have delved into its inner workings in any sort of detail, and even fewer still bother to write about their findings. The fact I can find very little on jetting a 1000-series for use on a Gold Star, and nothing about the air passage, probably means that either: 1) no one has studied 2/4-stroke modifications for the carburetor in this detail, or 2) people who modified the air passage found they made it worse, but no one publishes the results of negative experiments. The second possibility is why I'm proceeding very, very carefully.

-- the fact you remove the air jets from Mark 2 Amals is consistent with 4-strokes liking to have a lot of flow through that air passage, i.e. consistent with me drilling out the present 2-stroke obstruction.

-- the 2-stroke configuration of the Mark 2 uses a smaller air jet than the 4-stroke to enrichen the mixture at the low end of the range where the slide has its biggest effect. I don't think it's a coincidence that Rich B finds his #3 slide a bit rich while JakeH says he gets good results with a leaner #3.5. Neither mentions having drilled that air passage.

-- Although operation of the slide cutaway, air passage, and spray tube overlap, they don't completely compensate for each other as evidenced by the existence of different spray tubes for "normal," "Trident/Rocket3," and "Norton."

-- Although Amal produced three 4-stroke spray tubes, it's impossible that only three configurations could accurately control the mixture for every camshaft and every head. So, it's very likely that the "best" shape for the spray tube in a Gold Star is one that never existed.

-- If I do drill out that obstruction and find it was a mistake to have done so, it is relatively easy to return the original configuration by means of a bespoke air jet. In contrast, metal removed from a slide to make it leaner can't be replaced.

Posted By: 998John

Re: Correct needle for 1000-series Concentrics? - 03/24/19 6:33 pm

This is a good article from John Healy on understanding Amal carbs.


Attached File
Amal l John Healy.txt  (35 downloads)
Attached File
Amal ll John Healy.txt  (32 downloads)
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/24/19 6:46 pm

Originally Posted by 998John
This is a good article from John Healy on understanding Amal carbs.
I have John's articles in the 3/4"-thick 'Carburetor' tab of my bespoke Gold Star manual, and they are good, but unless I missed it he doesn't discuss the 2/4-stroke Concentric "air jet" issue that's vexing me.
Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 03/24/19 9:05 pm

We did change the spray tube also to an uncut 4 stroke type on the Gold Star.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/24/19 9:43 pm

End of MK11 doc by John Healy, air jet gets a mention.

"It is interesting to note that there is another air bleed located at the middle of the front of the carburetor. By varying its size one can increase or decrease the vacuum produced by the venturi effect. It will affect the fuel delivery through the needle jet across most throttle openings. The size of this air bleed is a compromise and is seldom altered. "

Bearing in mind that I am normally wrong, here goes anyway. 2 strokes breath twice as much as 4 strokes, this must make big differences in setting up jets for same size chokes. I have never messed around with air jets, but, your plan to drill and plug with options seems like a reasonable one. So long as they are easy to change, is there enough meat to tap a thread for screw in jets?

Thinking out loud bearing in mind JHs quote above, if you open up the air jet that will dilute the venturi signal and make less signal at the needle jet, weakening the mix compared to a smaller air jet? Or have I got this back to front?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/24/19 10:06 pm

Originally Posted by RPM
We did change the spray tube also to an uncut 4 stroke type on the Gold Star.
Did you use a spray tube from a 600/900 Concentric? I believe it was Kerry W who in an earlier post in this thread pointed out a 1036 was used on the last of the Velocette Thruxtons. An Amal book shows that indeed it was, with a note in the "Special Details" column saying it has a 1034/070 Air Tube. I haven't been able to find that part number listed elsewhere yet but it's tempting to think it means spray tube. However, that same column lists either 'air tube' or 'spray tube' for various other carburetors so it's not clear they mean the same thing.

Originally Posted by gavin eisler
End of MK11 doc by John Healy, air jet gets a mention.
I should have said that he doesn't discuss the "air jet" in the Mark 1, i.e. that 3/16"-dia. tube running from the front that has a constriction in the 2-stroke 627 and 1036/1038.

Originally Posted by gavin eisler
if you open up the air jet that will dilute the venturi signal and make less signal at the needle jet, weakening the mix compared to a smaller air jet?
Exactly.

If any of you, too, ever become obsessed with the issue of spray tubes you will find that some people have written they believe a non-cylindrical tube decreases the relative pressure difference at the outlet (which would weaken the mixture), while other people believe it increases the relative pressure difference (richen the mixture).

Rather than belief, if I had examples of at least three of the four spray tubes in carburetors of identical bore I could put them on my flow bench and measure the pressure under identical flow conditions to obtain actual data to answer this. I have the instruments to measure pressure differences with a resolution of 0.001 psi which certainly should be sufficient.

It happens that I already have a 932 Concentric with a Norton spray tube. A little research found that a 932 also was used on some BSA 650s and on the B50MX, presumably with flat-cut spray tubes, as well as on a number of Bultaco and other 2-strokes. A little more research showed that if I waited long enough for them to turn up on eBay and was willing to spend ~$150 I could buy the "missing" two carburetors in order to conduct this experiment.

The thing is, I don't want to spend $150 of my own money to get these carburetors and then spend the time making measurements to answer a question that should be of general interest to more than a few others. So, I'm proposing to crowdsource this experiment. If someone(s) else is/are interested in having the answer, send those two missing carburetor bodies to me (flat top and slant-cut spray tubes). PM me for the address if you want to send the carburetor(s). Feel free not to take the time to disassemble anything, but all I actually need are the bare bodies as shown in the photograph. I would swap the same slide, cap and jets between the bodies for the measurements so the only the spray tubes would differ. If a few of you are interested enough in knowing the answer to send worn-out bodies to make the measurements happen, that's great. If not, that's OK too.


Attached picture Concentric_Norton.jpg
Posted By: kommando

Re: Correct needle for 1000-series Concentrics? - 03/24/19 11:42 pm

I use a Norton 850 932 carb on a ported to match B44 fitted with B50mx cam, kept the stepped spray tube and matching needle. After tuning the main jet it runs cleanly through the rev range and throttle openings.
Posted By: JakeH

Re: Correct needle for 1000-series Concentrics? - 03/25/19 2:09 am

Yes both wanted the same except the main, Now i did not spend lots of time making sure the pilot was spot on since it was a race bike. The street bike idled and started very well with the
30.

The spray tube is the same for the 900 and 1000 series. I usually push one out of an old 900 series carb and put it in the 1000. I have never tried to get a new one. they shouldnt wear.

As for Power.
The last race engine was 9:1 with big cams, lots of head work, pearson crank. single plug was 41 hp at 7k still Climbing. This was with a 1038. I have checked the GP and they are worth about 2- 2.5 hp over the 1038. Only at the very top, the 1038 works great everywhere else!!

As for the street bikes, the most with a stock muffler make 26-29, and with aftermarket straight thru muffler are 31-32.. i have a original BSA muffler that i need to try, I have a feeling the
new repro mufflers are not made for performance these days!!

All interesting stuff!!!
Let us know what jetting you came up with!! and how you like the carb !!
Posted By: geordie

Re: Correct needle for 1000-series Concentrics? - 03/25/19 9:30 am

My 1038 experience has not been great, When I got the bike it had a brand spanking new carb that hesitated slightly when opening the throttle off idle, not badly but enough to be annoying. I looked into the jetting and eventually worked out it had the 2 stroke setup, angled spray tube, with 3 1/2 slide 107 needle 30 pilot the needle is stamped 0 and 380 main. I decided to change to the 4 stoke setup. got an uncut spray tube (incidentally off a 932 that had lived happily on my Norton Commando for years) I bought the Amal conversion kit numbered 622/235 consisting of jet holder , 106 needle jet and needle 622/124. It now runs far worse. I got myself an AFR meter and put the sensor into the front end of an old muffler. I can get it running a smooth Idle at 14:1 AFR but as soon as I open the throttle it runs rough and goes full lean on the AFR meter. Unfortunately I haven't really had time to really get stuck in and try tweeking things I only get 1/2 hour here and there to spend on it
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 03/25/19 12:58 pm

"At first I thought it was Celtic for 'President'", spat my coffee out, Laugh of the day for me.

No less an authority than Rupert Ratio thinks that slash cut spray tubes are richer than flat tops, its the only reference I have handy, I had a good 2 stroke tuning book that covered carb details , but i lent that to someone and it never came back.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/25/19 4:24 pm

Originally Posted by kommando
I use a Norton 850 932 carb on a ported to match B44 fitted with B50mx cam...
Originally Posted by JakeH
Let us know what jetting you came up with!! and how you like the carb !!
As shown in the first photograph, some years ago I modified a "universal" probe sold by Innovate Motorsports to go with my Innovate LM-1 air/fuel meter in order to make it suitable for motorcycles. However, the probe has two limitations, one more serious than the other. The more serious limitation is that baffles can keep the probe from being inserted very far in some exhausts. The less serious limitation is that, especially with cams with a lot of overlap, fresh air is sucked some distance up the pipe every other revolution which would otherwise invalidate the readings. To overcome this I made a "Bunsen valve" from high temperature silicone material that wraps around the silencer, opens to let exhaust out, but closes when the pressure drops to keep air from being sucked in. Still, the silicone material flaps in the breeze so it isn't suitable for really high speeds or for long distances.

Anyway, in thinking about working out the optimum jetting with my 1036 and 1038 Amals I realized I have another choice for attaching the air/fuel sensor to Gold Stars. Part of my hoard of BSA parts is a Gold Star pipe to which a homemade megaphone had been welded, shown in the second photograph. By cutting the megaphone off and welding a bung for the sensor I can use this pipe on any of my three Gold Stars with their three different silencers.

I have an original Innovate LM-1, made in the dark ages of limited data storage, so it "only" can collect data for 44 minutes from 5 inputs at 12 Hz. I have it configured to collect air/fuel, rpm, and throttle position. The latter by means of a "universal" bracket and potentiometer that I friction couple to the throttle. Rotating the throttle between closed and WFO a few times with the engine off establishes the voltages corresponding to the throttle extremes.

Innovate's current model LM-2 records at the same 12 Hz as my LM-1, although it can record 32 channels vs. only 5 for my LM-1. However, this isn't of any use to me since I only use 3 channels anyway. LM-2 data is recorded on a 2 GB card so presumably recording time is longer than the 44 min. of the LM-1, but I haven't found that time to be any sort of practical limitation. If I ever decide I have to fully instrument the V-8 in a Boss Hoss I'll have to upgrade to the LM-2, but the LM-1 should continue to do nicely until then.

Originally Posted by geordie
3 1/2 slide... got an uncut spray tube... as soon as I open the throttle it runs rough and goes full lean on the AFR meter.
Originally Posted by gavin eisler
No less an authority than Rupert Ratio thinks that slash cut spray tubes are richer than flat tops,
No less an authority than Stoor Regan emphasized the need to "Trust, but Verify," but taking this at face value the problem geordie is having may be fixed with a #3 slide. If his replacement uncut spray tube did indeed weaken the mixture that, plus the weaker #3.5, could be what is causing the behavior when the throttle is first opened.

The 1970 Thruxton used a R1036/4, presumably with 4-stroke spray tube, with 320 main, 30 pilot, .106 needle jet, needle on position 1, and #3 cutaway. These settings should be pretty close to what are needed on a Gold Star.

Tying up one loose end, I heard back from Burlen/Amal today confirming that all series of Concentrics, including those of the Mark 2, use the same 622/074 4-stroke spray tube. Still open is the question whether the air passage should be 3/16" all the way. I sent a subsequent question to Burlen about this but haven't received an answer yet.[*] Given that it is unlikely they produce that particular carburetor it's possible no one at the "new" Amal will know the answer.

[*]I've now heard back with an answer to this question. All of the 1000-Series bodies were made in Spain and they only have one machining drawing for the body. It shows a 4.75 mm (0.187") air passage that reduces to 2.5 mm (0.0984") near the far end.[**] The email says the 1036/001 body number also was used by Maico and since had the body been modified for Velocette it would have a different part number he speculates that the air passage dimensions were the same for both. This makes sense since, as they say, beggers can't be choosers and by 1970 Velocette was in no position to insist on much of anything. According to Ivan Rhodes's book, only 140 Thruxtons were made in 1970. So, my speculation is that if Velocette could have had carburetors made that provided optimum performance on the Thruxton they would have had that passage drilled 4.75 mm the entire distance. Instead, they had to make do. But, that's speculation that can't be checked. In any case, I'll proceed to try to determine the best possible jetting without drilling out that passageway.

[**]I previously wrote that I found the restriction to be 0.082". In light of this recent email from Amal I remeasured the passage in the 1038 and found some machining swarf at the end was causing a restriction. With the swarf pushed out of the way a #41 drill bit (0.096") goes through the passage but a #40 (0.098") does not.

Thruxton Addendum: Thruxtons used 1-3/8" (35 mm) Amal GP carburetors during 1965-68, oddly dropping considerably in size to 930 Concentrics for 1969, but then back up to 1036 for the final year 1970. In his book 'Velocette' Rod Burris says "The last few Thruxtons to trickle out were fitted with Concentrics, although whether this is due to the infamous 'loss' of a large batch of new GPs is uncertain." Maybe the "infamous 'loss'" is described elsewhere in the book, but GPs were considerably more expensive than Concentrics so a company on life support might not have had the funds to recover from a major theft. Also, the drop in size all the way to 930 makes me wonder if there was no available stock of 932s they could substitute by the time the theft was discovered.

I would have thought all 360 cc Bultacos would have been users of the Spanish-made 1000-Series but, with the exception of the TS350 that used the 1038 starting in 1970, most used 932s through at least 1971 (maybe others began using 1000s later, not covered in the 'Amal Reference Catalogue'). Other than the Thruxton and TS350 Bultaco, the only other users of the 1000-Series that I spotted in the 'Catalogue' were AJS that used the 1034 during 1970-73, Boudet (French) the 1036 during 1973-74, CCM the 1034 and 1036 in 1974, Greeves the 1034 during 1972-74, and Maico the 1036 during 1971-74. It appears the Mark 2 came on the scene around 1975 in sizes up to 40 mm so I suppose it was about then that the 1000-Series went out of production.





Attached picture Innovate_probe.jpg
Attached picture DBDexhaust.jpg
Posted By: geordie

Re: Correct needle for 1000-series Concentrics? - 03/26/19 11:33 pm

I have investigated further , now the slide is marked 3 1/2 which equates to .21875" but I measured the cutaway at.172" at the outer circumference, which i believe to be somewhere between a 2 1/2 and 3 cutaway. The idea i was toying with was to machine some off the bottom af the slide to effectively reduce the cutaway (and maybe lift the needle to compensate)
This is based on my belief that the cutaway number is equal to 1/16" is this correct? Could someone measure another cutaway and report for comparison ?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/26/19 11:54 pm

Originally Posted by geordie
Could someone measure another cutaway and report for comparison ?
The slide in the photograph is marked '2½' and as can be seen the cutaway is two and a half 16ths. Sit it on a flat surface and view the ruler straight on at the height of the cutaway because otherwise parallax will cause a significant error in your measurement.


Attached picture Concentric13.jpg
Posted By: JakeH

Re: Correct needle for 1000-series Concentrics? - 03/27/19 2:18 am

Magneto Man

I use the same unit that connects with my dyno unit, and tapped the end for a 1/8 pipe fitting, and install a length of copper pipe to
get further up the pipe. I also made an old pipe my "dyno Pipe" with a o2 bung just below the bracket. It works best!!

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/27/19 3:33 am

Originally Posted by JakeH
install a length of copper pipe to get further up the pipe. I also made an old pipe my "dyno Pipe" with a o2 bung just below the bracket. It works best!!
The reason the bung in the exhaust pipe works best is the exhaust gas flows by it. A length of Cu pipe relies on diffusion to get the gas from the end all the way to the sensor and that doesn't work very well at all. My probe, modified from the one Innovate sells, has an "inlet" and an "outlet" pipe that sit at different points in the exhaust stream so there's a pressure difference that forces a flow of exhaust gas over the sensor. I added a spacer on the inlet tube to make sure it can't sit flush against the exhaust pipe where the flow is stagnant.


Attached picture Innovate_probe2.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 03/27/19 3:57 am

MM: Interested to recall that some Thruxtons were dispatched with a 930 - as mentioned in the table in Rod Burris' book (noting that the 930 specification quoted is the same as the same as the Venom from the year prior..odd that both bikes required EXACTLY the same jetting, despite different cams, heads, pipes..not sure I trust that data..never minding the fact that Veloce would choke (pardon the pun) at using such a small carb on the VMT, especially when at least the 932 would have been available.)..as a former Thruxton owner (1966, #409) I have the usual literature, though nothing would surprise me at this distance from when they were made. (Mine came to me with the usual 5GP2 and left with a 36mm VM Mikuni. The GP worked fine...the Mikuni transformed it!).

The interesting part came when I transplanted identical 36mm Mikunis onto the Thruxton and (UK) Clubmans DBD, at the same time...the Thruxton was very simple to get the jetting very close, though the BSA took 3x the effort and ran very different jetting...the different jetting was what surprised me. Both were 'standard' (by accepted parts book references!) in terms of cams and pipes.

With respect to air jets, tread carefully. Changes in this regard should not be made to effect changes in any specific area of jetting - the effect of the air jet is to alter the whole slope of the fuel curve. The same overall results can be obtained with different air jets via correspondingly different jetting.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/27/19 5:12 am

Originally Posted by Kerry W
With respect to air jets, tread carefully.
Indeed, caution is wise. At the moment I'm torn between an OCD desire to understand the 2-stroke to 4-stroke conversion at a deep level, and just getting it working reasonably well.

Presently I have the carburetor set up with specifications given elsewhere in this thread so it should at least work. I hope. It would have been easy enough to swap the spray tube but I decided to leave it as-is on the first round of jetting. The bung for the air/fuel gauge is due on Thursday so by Friday I should have it installed in the exhaust system I "discovered," and everything in place on the Competition.

I haven't heard anything from DocZ so I can only hope the rear roller shows up soon. Even absent it I'll try it again with the new abrasive on the rear roller so, as I said before, I hope to have the jetting worked out by sundown on Sunday (unfortunately, that's the same hope I wrote a month ago...). Re-reading this post, I used the word "hope" more times than I would have liked.

Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 03/27/19 8:17 am

I'm in commercial aviation...I try to avoid using 'hope' at all times!
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/28/19 1:19 am

Originally Posted by Kerry W
I'm in commercial aviation...I try to avoid using 'hope' at all times!
I'm on commercial planes quite a bit so my hope is the pilots always rely on skill rather than hope. I also hope I don't find myself on a 737 Max 8... Going off on a tangent, I'm reminded that some years ago an out-of-town technician repaired my electron microscope. As he was ready to leave that afternoon he opened his briefcase to check the flight time and I saw the only two other things in there were a radar detector and a bible. Returning to airplanes, I'd much prefer to have pilots who go over the checklist a second time rather than spend that time praying they don't screw up and crash the airplane.

Instructions for locating the oxygen sensor are that it should be at least 24" from the exhaust port to be sure it does not exceed 900 °F/ 500 °C At that temperature steel is just starting to have a faint glow, which I've never seen even near the head since the Gold Star's pipe hangs in the breeze instead of being insulated under the hood of a car at the end of a header fed by four cylinders. The (heated) sensor also should be as near as possible to the top of the pipe so water condensation doesn't hit it when the engine starts up and kill the sensor due to thermal shock.

Anyway, I sawed the megaphone off at the weld to leave the pipe as long as possible and swapped it for the Competition's pipe and silencer for measurement purposes. The location I chose (which also satisfies the instructions for it to be after the Gold Star's turbocharger but before its catalytic converter), is shown by the red 'x' at the intersection of the two pieces of blue tape in the first photograph. This will place it in a protected spot ~21" from the exhaust port.

For aesthetic reasons only it would be nice if the sensor were vertical so as the second photograph shows I used the smallest protractor I have to determine the approximate slope of the pipe there to be ~22-deg. The pipe is curved so this isn't an exact measurement, but by milling the base of the bung at this angle it will be pretty close. Locating the bung with respect to the horizontal portion of the end of the pipe should get me even closer, but that remains to be seen.

As the third photograph shows the bung arrived late this afternoon, a day early. So, with luck, it will be welded in place to hold the sensor perfectly vertical tomorrow.

Cautions are to be found that the lifetime of these wide-band O2 sensors is degraded by the use of leaded fuel, gasoline additives, excess oil in the exhaust, and oil with high Zn content. Luckily, none of those are issues with old British motorcycles...

On another note, the Stellite-tipped pushrods I made for my 1928 Ariel survived the ~3000 miles of the Cannonball with flying colors, and I also used Stellite to repair the lifter that had worn a hole in it. Although I have 1 lb. of 3/32" TIG rods, the smallest size that is "mass produced," it's too large for detailed work. Some of you might remember that at the time a company generously gave me 5 rods of 1/16", which is what I used on the Ariel. Anyway, because I hate not having something as useful as this available if/when I need it I've been looking for a source of inexpensive 0.045" TIG filler since October. Despite extraordinary -- for me -- patience, nothing turned up over the past six months so I bought 1 lb. of 0.045" at full retail, which is ~3x more per pound than it goes for in larger sizes. The general principle with TIG is a too-small rod always can be used, whereas a too-large one is a problem, so this Stellite should serve my purposes well into the 22nd Century.


Attached picture AirFuel01.jpg
Attached picture AirFuel02.jpg
Attached picture AirFuel03.jpg
Posted By: 998John

Re: Correct needle for 1000-series Concentrics? - 03/28/19 2:39 am

MM
Which grade of Stellite do you use?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/28/19 3:30 am

Originally Posted by 998John
Which grade of Stellite do you use?
Stellite 6. Known generically as ErCoCr-A and sold by various companies under names like Polystel 6, Stoodite 6, Bishilite 6, etc.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/29/19 3:40 am

I didn't have time to get the pipe completely modified today, but I made a lot of progress. I center punched the pipe while it was in place so I would know exactly where to drill. Slicing the bung at 22-deg. would have removed more of the threads than I would have liked, and I didn't want to order an extended bung and wait until next week for it to arrive, so instead I fabricated a short spacer from a piece of 1"-OD heavy-wall stainless tubing. I sliced it at 22-deg. on the mill then rounded the base using a 1½" end mill, finishing the match to the 1¾"-OD pipe with a die grinder. As can be seen the top of the spacer isn't quite level with the rear portion of the pipe, but I had a plan to deal with that.

After welding the spacer to the tube I put the pipe in the mill, holding the rear portion with the vise and making sure it was properly vertical by means of a 'L' fixture and a bracket bolted between it and the mounting bracket of the pipe. I then milled the top of the spacer flat and parallel to the rear of the pipe.

That's as much time as I had today. Tomorrow I'll weld the bung on the spacer and, if nothing goes wrong, will be done with the modification. I'll remove the 'twitter' silencer from the bike's actual pipe and bolt it in place on this modified pipe. I'll plug the bung until I get the jetting reasonably close and then install the wideband sensor and go hightech on the mixture.

I realized I haven't used the Innovate with my current computer. But, hey, it's only software so there couldn't possibly be any issues...


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Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/29/19 10:34 pm

Originally Posted by Magnetoman
I realized I haven't used the Innovate with my current computer. But, hey, it's only software so there couldn't possibly be any issues...
Who could have possibly predicted there would be computer issues? A half-hour of effort didn't solve the problem, but I have hopes that a new cable due this afternoon will. The LM-1 (and my Superflow flow bench) was made back in the days of RS-232 serial ports, whereas any computer made in more than a decade has USB serial ports. The problem arises because the standards of these two differ in ways that require adapters that contain electronics, and even then a given adapter may work to connect some devices to some computers, but not necessarily the same devices to different computers. Further complicating things have been the ever-moving USB goalposts (1.0, 2.0, 3.0, 3.1, 3.2, ... ) which is one reason why cables that worked on past computers might not work on present ones.

Anyway, a Sewell cable was unrecognized by my computer (a Thinkpad). Although a Belkin cable that worked with my previous Thinkpad and the Superflow was recognized by my current computer as being a Belkin cable, and it got the LM-1 to display "serial interface" as if it were properly connected, still the LM-1 wouldn't communicate (note to self: test whether current computer connects to Superflow). I found on the web that someone managed to connect their LM-2 using a Tera Grand Premium cable so I ordered one, due later this afternoon. Again, the fact that cable worked with a different device (LM-2 vs. my LM-1) and (likely) different computer doesn't necessarily mean it will work for me so this is a $12.50 gamble.

Meanwhile, I finished welding the bung to the pipe. Because the sensor is a little way around the bend it can't be seen through the end of the pipe, but the borescope shows it is nicely positioned to inhale the exhaust fumes that will be streaming by. And, the extra effort resulted in the sensor being vertical, as shown in the third photograph.


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Posted By: geordie

Re: Correct needle for 1000-series Concentrics? - 03/29/19 11:58 pm

Nice work with the sensor , i positioned mine at the front of the silencer so its a bit further back at the rear of the gearbox, I have only used it briefly but I think it works OK. I didn't have a spare header or I would have done the same.
Does anyone know what sizes the small ports are that are in the bottom of the 1038 body either side of the slide ? I'm wondering if the secondary port may be undersize or partially blocked on mine.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/30/19 1:19 am

Nothing but frustration so far with getting data from the LM-1 to the computer. After a half-dozen downloads, driver updates, removing and reinstalling programs, and reboots I can get the computer to display real-time data from the LM-1, but if I try to download a recorded file from the LM-1 to analyze the program that Innovate supplies for this (Logworks) just disappears a few sec. after I click on 'connect'.

All is not lost while waiting for a hoped-for fix from Innovate's support staff since I can read the air/fuel ratios from the LM-1's display and memorize those figures at various throttle positions (as I ride down the road trying not to be distracted too much...). Being able to calmly look at a plot that also has rpm and throttle position displayed certainly would reveal more than doing it that way, but it will be much better than nothing.

Originally Posted by geordie
i positioned mine at the front of the silencer
The header I'm using must have been shortened before the megaphone was welded on. I have a rusty silencer with a long 1¾" exit pipe that I can cannibalize to extend the header but I don't want it to be either too long or too short so I need to make some measurements from the three Goldlocks... er, Gold Stars to get it just right. I would like it of a length such that silencers properly bolted on the frame and mated with the pipe don't have any issues with air leaking in. Too long isn't necessarily better than too short because the pipe could interfere with baffles. Anyway, it's one more thing to do.

Originally Posted by geordie
Does anyone know what sizes the small ports are that are in the bottom of the 1038 body either side of the slide ? I'm wondering if the secondary port may be undersize or partially blocked on mine.
If you're referring to the two tiny passages adjacent to the slide on the engine side of the carburetor, I haven't measured those but easily can if that's what you need. If you're referring to the compensating air passage down the centerline to the jets, in all three series (600, 900, and 1000) of 4-stroke Mark 1 Concentrics it's ~0.189"-dia.. However, in a 627 from a Bultaco Sherpa-T the air passage necks down to ~0.098"-dia. just before reaching the jets. The same ~0.098" constriction is in the much larger 2-stroke 1036 and 1038.
Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 03/30/19 7:56 pm

"waiting for a hoped-for fix from Innovate's support staff"

Good luck with that. I have the Innovate MTX-L wide band air fuel ratio gauge along with 3 other of their gauges including manifold pressure/ shift light which gives me rpm and exhaust gas temperature. Like you, it's nice to have the ability to see A/F in real time, but not much use unless you know other info at the same time. So I opted for their Pocket Logger with SD card so all gauges and the logger are daisy chained together. All I have ever been able to log is about 8 seconds of any run after which it quits logging. Calling their support staff for advice, the only answer I ever got is that "our gauges are made for new bikes so it might not work on yours."

The MTX-L also has additional inputs and outputs for power and lights as well as a 0-5v output which I can connect to my Performance Trends dyno software on my homemade chassis dyno and after inputting the calibration data, generates good data along with my torque, hp, exhaust gas temperature, and has several unused inputs for further use. I'm using Windows 10 on a dedicated computer for all my data.

They did tell me that I was probably getting interference from the ignition system, but somehow it works fine with the P.T. software on the dyno.

https://www.innovatemotorsports.com/products/mtxl_plus.php

Tom
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/30/19 9:13 pm

Originally Posted by koncretekid
all gauges and the logger are daisy chained together. All I have ever been able to log is about 8 seconds of any run after which it quits logging. ... the only answer I ever got is that "our gauges are made for new bikes so it might not work on yours." ... They did tell me that I was probably getting interference from the ignition system,
Based on that, if they ask I'll tell them I'm using my LM-1 on a 2019 Harley to avoid the possible response of it not having been designed for old or foreign motorcycles.

Having a chain of instruments interconnected on a common bus is harder to shield against EM interference than the LM-1's system of a single shielded cable to the oxygen sensor and another to the auxiliary input. At least, knock wood, I not had problems in the past.

Other things came up so today had to be a short day in the garage. Which means I may not make my hoped-for Sunday evening deadline for having the jetting sorted out. I did have enough time to install the pipe and silencer and was pleased to find the pipe only a fraction of an inch shorter than it was when new. Hence, I won't have to cut, weld, and grind an extension, saving quite a bit of time. As the first photograph shows I have the sensor bung blocked off for the moment, and will switch to the air/fuel meter once it "feels" like I have the jetting close.

The second photograph shows the "jetting kit" I assembled for sorting things when I get it running and head out on the road. There's a 340 main jet in the carburetor now, so the kit has five each larger and smaller jets, baggies to keep them separate to make finding the next one easier, socket to change jets, screwdriver to remove the plug at the bottom of the float bowl, cup to catch the fuel to pour back in the tank rather than soak into the ground, screwdriver for the idle and pilot mixture screws, spanner to remove the carburetor, and Philips screwdriver for the top so I can change the needle clip. As long as the cutaway turns out to be OK this kit should get the jetting as close to correct as is possible on suburban roads and by feel alone.


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Posted By: kevin roberts

Re: Correct needle for 1000-series Concentrics? - 03/30/19 10:51 pm

i'll be very interested to see what numbers you get for AF.

i occasionally run an AEM AF unit and get the best performance at numbers other than what people predict.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 03/31/19 3:02 am

So MM, extrapolating your process, if the data could be accurately and adequately logged, you could lend your pipe and logger to any GS owner anywhere in the world and they could forward data to you for analysis, following which you could suggest jetting alterations. Following a successful final result, the 'kit' would be returned!

Just a thought...
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 03/31/19 3:39 pm

Originally Posted by Kerry W
any GS owner anywhere in the world and they could forward data to you for analysis, following which you could suggest jetting alterations. Following a successful final result, the 'kit' would be returned!
That's the best idea I've heard all day. Of course, it's 8am where I am so it's the only idea I've heard all day...

A revised idea is if someone lives in an interesting part of the world that's worth visiting they could fly the kit and me there and I'll interpret the data on the spot. Actually, I suspect the kit will find itself in the Catskills sooner or later. Later, at the rate progress is being made there.

Originally Posted by Magnetoman
If someone(s) else is/are interested in having the answer, send those two missing carburetor bodies to me (flat top and slant-cut spray tubes
I'm pleased to report that someone took me up on this and those two 932 carburetor bodies are due tomorrow, to go with the Norton body I already have. As usual, I won't mention who sent them unless they say it's OK. I already have an appropriate manifold for my flow bench which only needed a flange to hold the carburetors. As the photograph shows, I made the flange yesterday. Today I'll devise a fixture to hold the slide at various fixed heights in the carburetors so that all measurements on the three bodies can be made under identical conditions.


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Posted By: Andy Higham

Re: Correct needle for 1000-series Concentrics? - 03/31/19 7:29 pm

Returning to your starting rollers problem, My starter uses boat trailer keel rollers, the V shape helps keep the bike central
http://www.indespension.co.uk/-v-shape-rubber-rollers/752-na003.html
Posted By: Andy Higham

Re: Correct needle for 1000-series Concentrics? - 03/31/19 7:35 pm

These are the rollers I use
https://www.starterrollers.co.uk/
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/01/19 1:18 am

Originally Posted by Andy Higham
These are the rollers I use
Interesting. The guy who makes the DocZ claims a company in England ripped off his design, and yours look a lot like mine. I haven't found keeping the tire centralized to be much of an issue. I try to have the bike perfectly vertical when I hit the switch but never quite succeed, but when the rollers pull it in one direction I just lean it a little in that direction and it moves back to the center.

I spent the day finishing the mounting flange including making some modifications to what I previously made. The flange has a 1.5"-dia. hole in it but today I made a second set of carburetor mounting holes (so I now have 2" and 65 mm) rotated 30-deg. from each other, along with a second set of six holes for mounting to the fixture on the flow bench to allow either type of carburetor to be mounted vertically. Not that air would care if the carburetor were tilted, but I would. I also made an adapter with 33 mm bore to make it easier to seal 900-Series Concentrics, and large Monoblocs, to the flange.

I machined a small brass block that bolts to the inside of a 3½ slide that has a tapped hole for a 10-32 machine screw (actually two of them silver-soldered together) that rigidly moves the slide up or down. I also made a platform that bolts to the top of a 900-Series cap that serves as a reference surface for calipers to measure the height of the slide as well as supports an engineer's clamp to lock the slide into position. The screw that holds this platform also serves to block off the choke hole.

For anyone who thinks it's OCD to spend so much time on the flow bench, you don't understand. It's actually OCD on a much deeper level. I want the results of these flow measurements to use to decide whether or not to drill the air compensating passage of my 1036 before I then spend the time to jet it. All the while hoping the rear roller fixture for my DocZ gets here before I have to start it.


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Posted By: Andy Higham

Re: Correct needle for 1000-series Concentrics? - 04/01/19 3:12 pm

The company who DocZ claims ripped them off is http://www.solomotorcycleproducts.com/wordpress/
The one I posted earlier is only similar in having 2 rollers and 2 motors
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/01/19 5:05 pm

Originally Posted by koncretekid
"waiting for a hoped-for fix from Innovate's support staff"
Good luck with that. ...
An email was waiting for me this morning listing the instructions for connecting my LM-1 to the computer. Well, had I not already followed those instructions a number of times using three different RS232-to-USB converters, as I had explained in my emails to them this weekend, that might count as a useful response. So, I called, where I learned a different company had acquired Innovate sometime along the way and relevant technical knowledge and documentation of "legacy" products was lacking with the current staff. I learned this when I suggested at the end of a conversation whose most useful statement was "I'll see what I can find and get back to you" that maybe it was an incompatibility between the several-years-old firmware version I have on my LM-1 and the latest version of their Logworks software and asked if I could install an earlier version. Because of the buyout and staffing changes, they have no earlier versions.

Just before we finished it occurred to me that if they would make me a great deal on the basic LM-2, without oxygen sensor or anything else, we could bypass this problem. Unfortunately, he pointed out that all the connectors are different so this isn't even a possibility.

An advantage of never throwing anything away is I was able to find the installation CD that came with my LM-1 many years ago so later today I'll try installing it. But, for that to work requires Win10 to run a program written in the days of XP, and the version of Logworks on the CD not to be troubled by the later version of firmware on my LM-1. But, hey, in the world of software engineers, things that should work often don't, and things that shouldn't work sometimes do, so it's worth a shot.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/01/19 9:45 pm

I sacrificed a main jet by machining the OD down so I could slip the same tubing over it and the inlet to my digital pressure gauge. I also drilled it larger, which isn't needed for a static pressure measurement, but it made it easy to see how thick the wall was as I turned it down. A note in the Superflow Operator's Manual mentions that carburetor tests sometimes need to be run at a reduced test pressure, as opposed to the 30" H20 that might be used on a head. The manual gave 1" H2O as an example so I started out there but then doubled the test pressure which, as the photographs show, gave a manometer reading of 0.061 psi with the slide approximately half-way open (note: I didn't have the needle installed, but will for my actual tests).

The Superflow's feedback controller holds the pressure constant but, as can be seen, when the photograph was taken it happened to be 1% below the set value. However, since that is an instantaneous reading, averaging the readings over a short time would reduce the error to below 1% (nb. it's the flow rate that actually matters, but it too fluctuates by the same amount). Further, Superflow claims measurement repeatability of +/0-.5%, which is important for switching between carburetor bodies. Also, although the last digit on the manometer is uncertain, so its reading would be ~+/-2% for this measurement, for the actual measurements I can easily bump the test pressure up by 4x to increase the flow by 4x and thus drop the manometer uncertainty below 1%. The manometer's repeatability is claimed to be 0.2%.

My setup can measure effects at the 1% level, but will this be sufficient to look for relevant performance differences between the various spray tubes? Raising or lowering an Amal needle by one notch changes the mixture by ~12%, which certainly has an effect in the region where the taper is active. Mikuni gives a finer control of ~6% on their needles. Changing an Amal needle jet by one size (e.g. from .106 to .107) has a similar ~10% effect on the mixture, and needle jet wear of 0.0005" changes the mixture strength by enough to be noticeable, which is ~5%. Anyway, what these examples show is the ability to measure 1% differences between the three otherwise-identical carburetors will be sufficient to disclose what effects the spray tubes have at various throttle settings.

One other thing is I have a miniature Pitot tube for probing air velocity. I won't know until I try whether it will reveal any useful information about the actual air flow in close proximity to the spray tubes.

Update #2: It was a big day in the Shipping & Receiving Department: The two 932 bodies generously donated to the cause of science arrived in today's mail, then later UPS delivered the DocZ rear roller and the 1 lb. box of 0.045" Stellite 6.


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Posted By: geordie

Re: Correct needle for 1000-series Concentrics? - 04/02/19 8:56 am

i measured my 3 1/2 slide and I believe it is less than a 3. ??????? [Linked Image] here it is rhs next to a 3 from a 932 lhs [Linked Image] now I'm confused
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/02/19 2:40 pm

Originally Posted by geordie
i measured my 3 1/2 slide and I believe it is less than a 3. ???????
It is very easy to reduce the cutaway of a slide by machining/filing/sanding the flat half of the bottom of the slide. This also drops the needle by the same amount, as well as reduces the overall height of the slide. Increasing the cutaway takes more effort. Anyway, if you place those slides side-by-side I'll bet the one marked 3½ that seems to be less than a 3 is shorter than the one marked 3.
Posted By: edunham

Re: Correct needle for 1000-series Concentrics? - 04/02/19 6:59 pm

Magnetoman,
I left you a post under the ET ignition thread.

Ed from NJ
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/03/19 1:39 am

A simple estimate shows I'll need to make ~30 separate runs on the flow bench to collect all the data I want. So, I decided to approach this methodically, like I'm told a physicist would. It wouldn't be a good thing to get partway through the measurements only to realize I'd overlooked some relevant factor that required starting over.

I've equipped the carburetors identically, turned the pilot mixture screws all the way in to minimize that flow path, and set the idle screws such that light sneaking under the slide just disappears. I improved the way I mount the 3½ slide to the adjuster. This will be used for all three carburetors, as will the 622/124 2-ring 'standard' needle that I have on the middle clip, eliminating that variable.

Since the Superflow registers all the air that enters it, but only the air that got there by flowing through the main bore counts, it's important that there be no leaks. I found an air filter adapter that screws on the inlets and soldered a piece of brass shim stock to it. I used solder so I can reuse the adapter when these experiments are finished. I set the slide at some random height about halfway and measured the flow to be 22.62 CFM as shown in the first photograph and then screwed the adapter on and measured 0.00 CFM. So, allowing one digit of uncertainty, the leakage is less than 1/2000 = 0.05%, which is negligible. I'll do this check before and after each measurement.


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Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/03/19 4:38 am

Oooo....I like the 'blanking' setup to prove leakage or the volume of additional flow..It's likely I wouldn't have thought of that...despite using leak-down testers on my 2 strokes!
Posted By: geordie

Re: Correct needle for 1000-series Concentrics? - 04/03/19 8:33 am

Originally Posted by Magnetoman
]It is very easy to reduce the cutaway of a slide by machining/filing/sanding the flat half of the bottom of the slide. This also drops the needle by the same amount, as well as reduces the overall height of the slide. Increasing the cutaway takes more effort. Anyway, if you place those slides side-by-side I'll bet the one marked 3½ that seems to be less than a 3 is shorter than the one marked 3.

I measured the height of this slide at 1.883" Could you tell me the height of your 1038 slide? I dont have one to compare
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/03/19 3:19 pm

Originally Posted by geordie
I measured the height of this slide at 1.883"
Mine is 1.890"+/-0.004" This means someone having filed enough off to account for the difference you find isn't an explanation.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/04/19 4:30 am

A sad development is that my friend's motorcycle shop was completely destroyed by fire last night. He went home at 5, the fire started in brush in the alley around 6, and the wind managed to set the contents alight despite the building having cinder brick walls and steel doors. The Fire Marshall has the building sealed off so he can't go in yet but the video the fire department posted on their Instagram site makes it clear that the contents are entirely gone. As my friend said, "The roof is on the floor." The alarm company alerted him to return to his shop to find a 2-alarm blaze (i.e. the blaze was big enough that two separate fire companies were called to the scene to deal with it). Insurance can't hope to cover the emotional damage of having his life's work go up in flames in front of him.

Originally Posted by Kerry W
I like the 'blanking' setup to prove leakage or the volume of additional flow.
I didn't have much time today (nor will I until Sunday), but since I'll be swapping the slide between bodies and making measurements at different slide heights, I made a gauge to let me quickly set the slide height at 3/16, 1/4, 1/2, 3/4 and full. The full setting isn't actually needed (nor fully closed, which doesn't have slot on my gauge). It's not obvious from the photograph but I made the gauge from thinner Al than the thickness of the rod that operates the slide so I can clamp the rod while holding the gauge between the jaws.

As can be seen from the photograph, I also labeled the three carburetor bodies with a red marker to make it easy to see which is which without having to pick them up and peer inside each time ('S' for standard, 'N' for Norton, and '2' for 2-stroke). I also ran flow bench tests at several pressures to help me decide on the one I'll use on the actual measurements.


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Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 04/04/19 8:51 pm

Originally Posted by Magnetoman
A sad development is that my friend's motorcycle shop was completely destroyed by fire last night.


That is really sad to hear and I cant imagine how gutted you friend feels right now. Hopefully no people were hurt but nevertheless my condolences go to your friend.

John
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/04/19 11:33 pm

Originally Posted by George Kaplan
I cant imagine how gutted you friend feels right now.
I haven't managed to speak with him today, but your observation is right on the mark.

Trivial in the context of my friend's loss is I no longer own an A65 because he had my Lightninized Thunderbolt stored in the shop's back room for the past couple of years (along with his entire private collection of bikes -- jeez, it's gut-wrenching to think about this). Trying to look for something to be positive about, I've long wanted a Spitfire Mk 2 so I suppose this now gives me an excuse to look for one...

As an aside, the burned A65 originally belonged to my brother and he had loaned it to me to ride from where we lived in Orange County to San Francisco over the 4th of July weekend of the Summer of Love. However, the rear tube blew out before I got there causing me to spend two nights in a motel in Visalia (in a room with a thin curtain and a bright sign just outside my window that flashed MOTEL every 2 sec. all night) until the local motorcycle store opened. I fixed the tire and headed home because I had a job. My life may have taken a different path had the A65 made it to Haight-Ashbury that weekend.
Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 04/05/19 12:41 pm


Shudder to imagine MMan in a kaftan with beads and a doobie.. Who would educate us on the joys of ET ignition, for one?

For the shop owner, whom I know, among his backroom treasures was a vintage TD Yamaha 350 that he raced with some success in AHRMA races back in the day.

He had another endearing habit. When, on occasion, he took in a bike that was essentially DOA and beyond repair, or a crashed bike not work salvaging, he would get the engine running, just about. Then, surrounded by friends as the sun set, he would fire up the old wreck, clamp the throttle wide open, and wait to see how long it took before the engine blew itself apart.

Let's hope he is able to rebuild his life and business, if not his collection.

Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 04/05/19 4:27 pm

Originally Posted by NYBSAGUY

Shudder to imagine MMan in a kaftan with beads and a doobie..

You beat me to it!

[Linked Image]
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/05/19 5:34 pm

What was I thinking? That was after my Freshman year in college, and I'm quite sure I didn't have a credit card, so I must have had my pocket stuffed with cash. I'm pretty sure I didn't have an iPhone, either, so booking motels wouldn't have been easy, and navigation during the Age of Aquarius would have been by astrolabe.

A piece of my hippie A65 lives on. After I got the Catalina I "temporarily" borrowed the A65's Bates headlamp mount, intending to use only until I found a replacement. So, since this relic[*] is bolted to the Catalina all I need is a tie-dyed bandana to head out on the highway, looking for adventure, to relive those thrilling days of what could have been a misspent youth on a commune as seen in 'Easy Rider."

[*]"Many relics have a legend or history attached to them, which is supposed to add to their significance and mysterious efficacy. Even the smallest particle is believed to contain power." 'Collecting, An Unruly Passion: Psychological Perspectives', Werner Muensterberger (Princeton Univ. Press, 1994).
[Linked Image]


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Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 04/05/19 7:58 pm


The thread has been hijacked, and I am partly to blame. Mea Culpa.

Motels, Catalinas, Bates. Bates Motel - now that would have been a story.

Can we get back to needles and spray tubes, please?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/06/19 1:21 am

Originally Posted by NYBSAGUY
Can we get back to needles and spray tubes, please?
With Scott McKenzie on the iPod and the scent of patchouli oil wafting through the garage, over the past two days I've made a series of preliminary runs to help decide on a final test routine. I quickly realized that having the slide at preset positions is basically irrelevant when running the tests, although knowing the positions will be useful later when comparing with the "classic" oversimplified Amal carburetor tuning instructions (up to 1/8, pilot; 1/8-1/4, slide cutaway, etc.). Although the effect of the air compensation passage isn't small, I was a bit surprised not to find it any larger than it is.

I have enough reproducible data so far to have confidence in one result. So, hands raised, how many of you think a slant cut spray tube makes the mixture leaner (i.e. decreases the relative pressure above the spray tube at a given air flow and thus draws less fuel into the air stream than a straight-cut tube)? How many of you think it makes the mixture richer? You might think one of these two groups has to be correct, but that group is only partially correct. The air flow and pressures are actually more complex than you (or I) might have thought. I'll leave it with that annoying teaser for now because I'm in danger of being overwhelmed with data so there will be a pause while I connect a computer to the flow bench.

Like my Innovate LM-1, the flow bench has an RS-232 connector. So, like with the LM-1, I now have to try to get it to communicate with my computer.

Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 04/06/19 3:47 am

You could have put that doobie to good use, too. Smoke in the air stream provides a very good visual indication of where the air flow is laminar and where turbulence is setting in.
Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 04/06/19 5:21 pm

I will bite first.
The cut spray tubes will lean the mixture just off idle but will have little effect once the slide opens past slightly open.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/06/19 5:53 pm

Originally Posted by RPM
I will bite first.
The cut spray tubes will lean the mixture just off idle but will have little effect once the slide opens past slightly open.
Although the full story is going to be a bit more complicated than this, as a slightly oversimplified preview of coming attractions, a slanted spray tube increases the depression (i.e. enrichens the mixture) by ~20-25% across the entire range of air flow, from the slide being less than 1/8 open to full open.

I haven't measured the Norton stepped tube yet, and I am going to be very interested what the Pitot tube has to say about the air flow patterns near the tops of those tubes when I have time to make those measurements. My mention of air flow pattern isn't a random comment, but is because of what I've found so far but what I'm not saying any more about until I make more measurements.


Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 04/06/19 6:03 pm

Hey I had a 50/50 chance but some how my 50/50 chances seem to be 80/20 chances most of the time.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/06/19 6:49 pm

Originally Posted by RPM
Hey I had a 50/50 chance but some how my 50/50 chances seem to be 80/20 chances most of the time.
It's a scientific fact that all probabilities are 50/50 -- either something will happen, or it won't.[*]

The simplified description of a carburetor found in many books points out that the air flow through the main bore increases linearly with engine speed, but the pressure drop over the spray tube due to the Venturi effect goes as the square of the air/engine speed. Unless corrected, that would cause the fuel mixture to become progressively richer at high speed. So, a compensating air passage or "air jet" is incorporated to deal with this effect since the air flow through it also goes as the square of the air/engine speed.

Note that if this simplified description were even roughly correct the consequences would be huge. If the mixture were correct at 1500 rpm (where, according to Amal's simplified tuning description, the pilot circuit is out of the picture and only what passes through the spray tube matters), at 6000 rpm the mixture would be [6000/1500]2 = 16x richer without the "air jet." In other words, if I'm testing a carburetor on the flow bench with the slide fully open and then block the compensating air passage the relative vacuum in the jet chamber should increase by ~16x. The fact I measure only a ~20% change tells us the simplified description is oversimplified to the extent of near uselessness for quantitative purposes.

What is missing from the simplified description is the effect of turbulence on the pressure in the vicinity of the spray tube. Here is where I hope my Pitot tube[**] will provide some quantitative insight into the difference between 16x "predicted" and 1.2x measured.

[*] I gave this the name "The Bardeen Rule" based on a discussion I had with him. I pointed out to students that since John Bardeen was the only person to win two Nobel Prizes in physics, making him the smartest person in the world, we needed to pay particular attention to his wisdom. Many years ago I was having an argument with someone at a conference whether some particular effect would be large or small. Neither of us knew the answer, but that didn't stop either of us from arguing as if we were right. However, John Bardeen was sitting next to us so I asked him if he knew the answer. Basically, he gave reasons why the effect couldn't be negligible, but it also couldn't be huge, so it must be ~50% (in some normalized way). A few days later when I was able to look it up I found the effect varied in different materials but was typically between 30% and 60%, i.e. 50/50. Based on that I formulated "The Bardeen Rule": whenever you need a number but don't know what to use, pick a value in the middle.

[**] Not to be confused with a Hercule Poirot tube, which always finds the correct answer but is harder to insert in a carburetor.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/06/19 11:08 pm

Attached is the first set of results for people to contemplate.

Some important notes:
-- The results are reproducible from day-to-day and with carburetors removed from the flow bench, slide moved to a different body, then moved back and measurements repeated.

-- The flow bench has a feedback controller on the test pressure that wanders a little on either side of the setpoint. This causes the flow to wander, as well as the pressure that I measure. All of these effects could be reduced significantly if data were acquired by computer, but even though acquired manually the data on the attached plot data are of more than sufficient quality for present purposes.

-- The 932 body given to me with a "2-stroke" slash-cut spray tube has an air correction passage that is constant 0.193" diameter rather than being reduced to 0.089" at the inside end of the passage. To simulate the restriction I drilled a short length of a #12 machine screw to serve as an "air jet." Whether or not the location makes a difference, note that this air jet sits on the outside end of the passage, not the inside end.

-- Marked below the CFM values on the graph are the positions of the slide. Because of the geometry (i.e. the slide cutaway) I wouldn't expect a perfectly linear relationship between slide position and air flow but, as can be seen, it is reasonably close.

-- What I've measured is the pressure depression in the jet cavity with the main jet blocked (by the manometer), so how to interpret these results in terms of air/fuel mixture is subject to later discussion.

My original question was what effect does the restriction of the air passage have on a 2-stroke 1036 body, so these first results address that question. The upper pencil curve shows the depression I measured as a function of air flow in the carburetor body with no restriction in the 0.193"-dia. air correction passage. The curve in red shows the depression with the passage completely blocked. The simple (simplistic) model of a carburetor would say under this condition of a blocked passage that the depression should increase as the square of the air flow, in which case it would be 100x larger at 80 CFM than at 8 CFM. Instead, it is only ~6x larger.

Again looking at the red curve, up to ~1/2 throttle blocking the passage does (slightly) increase the depression, but from there up to nearly full throttle it actually decreases the depression. That is, while depriving the jet cavity of compensating air "should" increase the depression, instead it decreases it over this range of air flow.

With the 0.089" air jet in place at the inlet to the compensating air passage, the depression is reduced over the entire range of air flow with respect to that of the unrestricted 0.193"-dia. passage. Again, this is contrary to what might be expected from the simple model of a carburetor, since restricting the compensating air getting to the jet cavity "should" result in increased depression.

Talk amongst yourselves.

Attached picture FlowBench08.jpg
Attached picture FlowBench09.jpg
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 04/06/19 11:46 pm

In my simple mind I see it like this, fuel has to rise , the slash cut means it comes out earlier, lower orifice less head required to lift , so less vac is needed to promote flow. Downstream will be more turbulent to promote better mixing ( maybe), 2 strikes need fuel for lub when the throttle is shut, the slash cut might also help to prevent seizure on a trailing throttle.
A 2 stroke is sucking twice as fast , drool from a slash cut will get lifted with higher velocities.
Just thinkin out loud.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/07/19 3:49 am

By practical experience, even high performance 2 strokes don't usually need fuel when the throttle is shut for lubrication - I have two types of carb on very high performance 2 strokes that have no pilot jet system and the throttle is completely closed when the twist grip is wound off. This is not uncommon at all.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/08/19 1:41 am

A technical paper kindly supplied to me by someone who will remain nameless (unless he gives the OK) explains that the problem the notched shape of the Norton spray tube ended up solving was caused by the silencers. With the new silencers the mid-range was too rich when the throttle was snapped open at 40 mph so the bike would bog down rather than accelerate. What they needed was a fix to give a leaner mid-range under these conditions.

I'm sorry about the messy first graph but I haven't taken the time to replot the data. But, looking at the curves on this graph, while the Norton spray tube provides a higher signal (bigger depression) to the jets across the entire range than the Standard spray tube, the signal is 28.6% larger at full throttle but only 20.6% larger at half throttle. This is the difference that was needed.

The plot shows there isn't much difference between the Norton spray tube and a 2-stroke tube used without a restriction in the air compensation passage. However, given that they must have tried the 2-stroke tube first, the difference with the notched tube must have been large enough, and/or the transient response when snapping open the throttle must have been different enough, that the notched tube provided the solution. Since the issue was 8-stroking when the throttle was snapped open it could be the mixture with the notch was still rich, but just "leaner enough" not to 8-stroke.

If I cared about Nortons I'd carefully measure the difference between the notched tube and the 2-stroke tube between half and full throttle. But, I don't, so I won't. However, I am interested in whether or not I should replace the 2-stroke tube in my 1036 with a 4-stroke tube, as well as if I should drill the 0.089" passage to the full 0.193". So, I carefully measured the behavior at low throttle settings, with the results shown in the second graph.

The graph shows that whether or not I drill out the air passage, the 2-stroke spray tube will give a ~20% larger signal in the region where the slide cutaway matters. This means a larger cutaway will be required with the 2-stroke spray tube than if replaced it with a 4-stroke tube.

So, what have I learned from working my fingers to the bone on the flow bench? I learned that the 2-stroke spray tube in the 1036 and 1038 provides a significantly stronger signal than would a replacement flat-cut spray tube. The measurements also provide an explanation for why the notched tube solved the roll-on throttle problem experienced by Norton. Over the range where the cutaway matters the signal from a 2-stroke tube is ~20% stronger so a slide with less cutaway likely would be required if changing to a 4-stroke tube. But, other than the 1036 needing a smaller main jet than if I swapped to a 4-stroke spray tube, there's reason to expect the adjustment possible with the needle height (and possibly the needle jet size) will be sufficient to take care of the mixture across the full range of throttle. However, if jetting proves problematic in the range above ~1/2 throttle with respect to that below ~1/2 throttle, the change in slope of depression vs. flow by removing the 0.089" "air jet" remains a possibility.

The only thing that remains to do is to see if the Pitot tube provides useful information about air flow near the exit of the spray tube. Oh, one other detail. Get the jetting sorted out in the Gold Star...


Attached picture FlowBench11.jpg
Attached picture FlowBench12.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/08/19 4:36 am

That is all pretty interesting. It might go some way towards explaining why some versions of Mk1 Concentric jetting I have seen are significantly different. I had put a certain amount of that down to operator 'indifference' and machine variations, though the spray tube, might be responsible for much of the variability, where Concentrics (specially large ones) have been transplanted onto Gold Stars..
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/08/19 3:24 pm

Originally Posted by Kerry W
It might go some way towards explaining why some versions of Mk1 Concentric jetting I have seen are significantly different.
A fair amount of what has been written about spray tubes on the web doesn't look very good in the light of this actual data.

I don't think I discussed my use of 7" H20 for the flow bench test pressure, which I settled on after a series of preliminary set of measurements. As to whether this provides a reasonable set of flow conditions, ignoring overlap, if the cylinder of a Gold Star completely and uniformly fills during the downstroke that's 500 cc / one-half revolution of the engine. Converting this to cfm vs. engine rpm:

rpm______throttle position __ CFM (500 cc x rpm x 2)
600 (idle)___~closed ________________5.3
1500 _______1/4 _________________ 13
3000 _______ 1/2 _________________ 26
4500 _______ 3/4 _________________ 39
6000 _______ full __________________53

Obviously, flow would be lower than these average figures when the intake valve was starting to open and when it was closing, and higher than average when the valve was fully open, but they give reasonable figures to check against. Note from the graph in an earlier post that a test pressure of 7" H20 resulted in ~85 cfm flow at full throttle, which is ~60% higher than the average flow calculated under operating conditions, so the flow bench settings I used put the carburetors in the right ballpark.

Changing the test pressure would change the flow, but unless there were a transition from laminar to turbulent flow that inconveniently happened at a somewhat higher or lower flow, doubling/halving the pressure would just double/halve the flow. My preliminary tests run between 3" and 15" H20 that caused me to select 7" H20 found no such unexcepted effects. Further supporting this is the absence of any abrupt change in the smooth curves of my previous post anywhere between 4 and 85 CFM. Also, to repeat something from a previous post, considerable work has been done with flow benches over the past three decades that established the validity of measurements made with the steady flow of a flow bench despite the interrupted flow of an engine.

I probably mentioned it before, but I used 932 bodies for my measurements because that's the size Norton used with their notched spray tube. This means 932s let me make direct comparisons between three of the four spray tube shapes that were supplied without having to deal with other variables (e.g. having to assume a correction factor for flow through bodies with different bores). For the same reason I used the same slide, needle, and needle jet for all the measurements -- only the bodies themselves were switched. Also, the 32 mm of a 932 is a reasonable size for a Gold Star. Although 1-1/2 (38 mm) GPs were used on 'Clubman' and 'Competition' models 1-5/32" and 1-3/16" (29.4 and 30.2 mm) Monoblocs were used on 'Catalinas'.

explanation of problem with text disappearing: for some bizarre reason text in the middle of the last paragraph is disappearing. It shows up when I 'edit' the post, but isn't there when I upload the changes. It's not just truncating the text, it's cutting a section out of the middle of the last paragraph. I'll try to solve this later.

OK, after several attempts that included removing characters like ", replacing the ASCII code for one-half by 1/2, etc., I found that things went haywire where the Britbike software replaced the word A-m-a-l with a link. Once I removed "four spray tubes that Amal supplied" and replaced it with "that were supplied" the text reappeared.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/10/19 12:48 am

Prior to deploying the flow bench I searched for data on spray tubes, or flow bench data on Amal carburetors in general. However, since that turned up nothing I believe this thread contains the only flow bench data of its type to be found in print or on the web. The findings are very interesting, to me at least, and relevant for anyone thinking of using a 1000-Series Concentric on a Gold Star or other large British single since most are in 2-stroke configuration. However, despite having posted data here three days ago there have been only two responses to it since then so I have to wonder if information of this type is too specialized to be of interest on Britbike.

Be that as it may, I'll now set the Superflow aside and, based on what I found with the flow bench data, begin work to jet the 'Competition' using a 1036 with the slanted spray tube and restriction in the air compensating passage, both as found on 2-stroke Concentrics, but with 4-stroke needle and jet holder.
Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 04/10/19 2:15 am

Information is always useful, especially if somebody else has done all the work to obtain it smile
Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 04/10/19 1:15 pm

Isn't using the slanted spray tube and a 4 stroke needle then same thing Amal was doing on the Norton 850's as the slanted cut spray tubes will richen up the lower opening but by using the 928/104 needles that are slightly longer keep the mixture a little leaner as the needle rises.

One trick we do sometimes when we have a bad flat spot in the middle when using megaphones is to enlarge the hole in the side of the needle jet. If I remember correctly we drilled it out from .035 to .039. What effect does drilling this hole out make?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/10/19 5:01 pm

Originally Posted by RPM
the slanted cut spray tubes will richen up the lower opening but by using the 928/104 needles that are slightly longer keep the mixture a little leaner as the needle rises.
One trick we do sometimes when we have a bad flat spot in the middle when using megaphones is to enlarge the hole in the side of the needle jet.
The flow bench measures the pressure difference acting to draw fuel out of the spray tube, but that's only half the picture. The amount of fuel at a given throttle setting depends on that pressure coupled with the orifice the fuel has to squeeze through which, as you say, depends on the needle and needle jet.

There's a reason that for each carburetor series the Mikuni book shows ~25 needles of different configurations, including some with double tapers, and needle jets spaced every 0.0004" (Amal's are spaced 2.5x further apart). While most of those needles are no longer available, they existed because they allowed fine-tuning the response even though engines might be similar.

I'll go out on a limb and speculate without checking that the needles and needle jets in the Yamaha SR500, XT500 and TT500 aren't the same. So, while I'm starting out with the 'standard' Amal 622/124 needle, .106 needle jet, and #3 cutaway in my Competition Gold Star I won't be surprised if that's not what I end up with. I'll keep your trick in mind about the needle jet if I run into that problem.

I still haven't done anything to try to solve the data transfer problem on my Innovate LM-1[*] (and the company has been non-responsive[**]), but a weather front is bringing very high winds (i.e. ~50 mph) today and tomorrow so no jetting will be attempted until things calm down.


[*] Success! (I think). Never throwing things away, and having somewhat of an organizational scheme for the mess, means it took less than 5 min. to find a CD onto which I had burned backup installation files of eight programs in 2009. So, I uninstalled the latest Logworks 3.37 from my computer and installed Logworks 3.01 from that CD. Crossing my fingers while doing this must have helped because, despite Vista having been the version of Windows at that time, and the LM-1 having newer, possibly incompatible firmware on it (it's 1.42b), Logworks installed on Win10 without error messages and the program had no trouble transferring and displaying the 5 sec. dummy file I had recorded on the LM-1. That CD took my LM-1 back to the future. Barring unforeseen glitches, this means I'll be able to log test sessions at 12 Hz for up to 44 min. and study them for insights (e.g. transients when the throttle is quickly opened) rather than trying to remember a few air/fuel ratios at specific throttle settings.

[**] An installation screen showed that the old 3.01 version of Logworks on my CD was "Updated April 2009." In searching their site I found newsletters showing it in beta in May 2007 and released for download in August 2008, so there's hope the April 2009 version is mostly bug free. I don't know when the current owners bought Innovate but the most recent press release on the site is from 2007, "In the Media" magazine article from 2008, and newsletter from 2011. Their current LM-2 was introduced over a decade ago, in the August 2008 newsletter, so it appears the company must have been acquired sometime around 2010 after which innovation at Innovate ceased, at least as far as portable air/fuel meters are concerned.
Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 04/11/19 1:59 am

Two points to consider are that there are 2 different 106 needle jets, one having the horizontal hole and a very different drilling although the lower part is probably the same size, and one not having the horizontal hole, as well as a couple other needle jets sizes, and the difference in the needle jet holder being shorter on the Norton, hence the shorter needle. So at least with Amal we have like 4 different needle jets times 2 different needle jet holders x 4 different needles times apparently 2 different air jets times at least a dozen different main jets times maybe 4 different slides and 3 different cut-offs equals 4x2x4x2x12x3 = 2304 possible combinations.

But compare that with Mikuni's almost infinite number of needle jets and main jets as well as slides, we may be lucky!

Tom

P.S. If anyone is interested, a gentleman we know as Beat in Switzerland on the B50.org forum, put a Mikuni 32mm flat slide on his BSA B50 and ended up making his own slide, needle (from an Amal needle) and even added a way to prime the Mikuni, but run well it does.
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 04/11/19 9:42 am

Quote
I'll go out on a limb and speculate without checking that the needles and needle jets in the Yamaha SR500, XT500 and TT500 aren't the same. So, while I'm starting out with the 'standard' AMAL 622/124 needle, .106 needle jet, and #3 cutaway in my Competition Gold Star I won't be surprised if that's not what I end up with. I'll keep your trick in mind about the needle jet if I run into that problem.

Well that was a safe speculation.
Yes different jetting on all of them , but again they all had different cams.
Add to that different jetting on SR's year to year and location to location
The SR's had a Keihin pumper with 2 way slide control
I used to get carb parts from this mob ( well their predessors to be accurate ) after Bradshaw moved to Bridgstone so I lost wholesale pricing.
Yam 500 carb kits
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/11/19 4:32 pm

Originally Posted by BSA_WM20
Well that was a safe speculation.
Does that mean I don't get a prize for being correct?

In case anyone is interested, and before turning away from the flow bench, the Superflow manual has various formulas for estimating engine parameters from flow bench data. One formula is for h.p. assuming a well-tuned engine with the maximum compression and right cams. These assumptions seem like they should apply to a DBD Gold Star. That formula predicts the flow I measured with these 32 mm carburetors would limit an engine to 43.5 h.p. The dyno certificate supplied with my 'Competition' claims it produced 41.7 h.p. (with a 1½"/38 mm GP), indicating the formula isn't far off, and that the engine might have a little more potential left to extract.

Although I haven't (yet) measured it, it's a good guess that the flow through a 1½" GP would be significantly higher than that through a 32 mm Concentric. This means that, since the carburetor isn't a limitation, h.p. gains (if any) are to be found in the head, not the carburetor. The formula predicts a gain of 0.35 h.p. for every increase of 1 cfm in flow so only a few cfm would make a worthwhile difference. That said, a head is more complicated than a carburetor, not only because of the more complicated shape of the inlet tract, but because the flow velocity matters as well.

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/12/19 11:51 pm

I got caught up enough on other things to have the time to install the DocZ "speedway" kit to the rear of the rollers today. The "speedway" unit pivots forward and back to adjust for wheel size and if it works as stated the thin black roller at the top of it will keep the bike from being pulled backwards onto just the rear roller. For at least the third time over the past months I'll state that I now hope to have the jetting sorted out by Sunday evening.

Attached picture DocZ_speedway.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/13/19 7:25 pm

Last week I wrote about the fire that destroyed my friend's shop. He is now allowed back inside so I drove over to see the devastation and to give him a backup of the shop's hard drive. After you look at the second photograph you will rightfully wonder how a computer could have survived that fire, but it did. Sort of.

The monitor and keyboard on top of the counter were melted but the computer itself was on a shelf under the counter and didn't have too much visible damage. Acting as his IT department I took the smoky computer from him, but when I connected it to a new monitor a code indicated the motherboard was dead. Despite that, I extract the hard drive, bought a docking station, installed the drive in it, and it worked. With not too many headaches I managed to copy the entire contents to a portable drive that I gave to him. Some years ago I had set him up to make regular backups of his computer but never was able to convince him to keep it or a second backup off-site. His on-site backup, on a different shelf, was melted so he was incredibly lucky the disk in his computer survived (the CD drive was on one side of the disk and the motherboard on the other side and apparently they provided just enough thermal insulation to keep the drive itself from getting too hot before the fire was extinguished).

Originally Posted by Magnetoman
Trivial in the context of my friend's loss is I no longer own an A65 because he had my Lightninized Thunderbolt stored in the shop's back room for the past couple of years (along with his entire private collection of bikes -- jeez, it's gut-wrenching to think about this). Trying to look for something to be positive about, I've long wanted a Spitfire Mk 2 so I suppose this now gives me an excuse to look for one...
The bad news for me out of all of this is, incredibly, I don't have an excuse to buy a Spitfire Mk 2. The fire started in the alley behind the shop and spread forward to the front. Although my BSA was at that back of the shop, it was in the far corner of a room off to one side. Somehow the roof over it didn't burn and the bike seems to have survived unscathed. The tank wasn't on the bike when I stored it so its absence doesn't have anything to do with the fire. The seat covering would be the most heat-sensitive part of the bike and it shows no sign of blistering. Amazing.


Attached picture Fire01.jpg
Attached picture Fire02.jpg
Attached picture Fire03.jpg
Attached picture Fire04.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/14/19 7:31 pm

Originally Posted by Magnetoman
install the DocZ "speedway" kit to the rear of the rollers today.
The reconfigured DocZ is now doing exactly what it is supposed to. The Gold Star, on the other hand, isn't. When I let out the clutch or compression release the DocZ keeps going but the rear wheel immediately stops spinning (a nice pile of tire dust is accumulating under the unit). I can (barely) push the bike with the compression released pulled in so it's not as if the gearbox or engine is locked up. After lunch I'll try again, hoping in the meantime the Gold Star has reconsidered its antisocial behavior.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/14/19 10:45 pm

Originally Posted by Magnetoman
When I let out the clutch or compression release the DocZ keeps going but the rear wheel immediately stops spinning (a nice pile of tire dust is accumulating under the unit). I can (barely) push the bike with the compression released pulled in so it's not as if the gearbox or engine is locked up.
Relevant background: A month ago the bike started on the 3rd kick and I made two laps of the driveway before stopping to adjust the idle, at which time it died before I could get the screwdriver to the idle screw (it was a "standard" too-slow-idle death; nothing dramatic just bang _ bang __ bang _______ pffft). It wouldn't start again but I gave up after a couple of kicks. I've been wasting my time on the flow bench since then so haven't done anything at all to the bike other than add gasoline today.

Leaving out the intermediate steps of today's non-starting diagnosis, eventually I removed the spark plug but doing so made essentially no difference to the difficulty in turning the engine over. If I rock the bike back and forth in gear with the spark plug out it alternately blows or sucks air through the spark plug hole so neither the gearbox nor engine is locked up, but it is much too hard to move the bike. Normally it is pretty easy to pull a bike backwards until the piston hits compression, but even with the spark plug out I can't do it. The problem might be obvious, but I'm at a loss to figure out what it is. Suggestions, please!
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/14/19 11:08 pm

It isn't a piston seizure, is it?
.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/14/19 11:17 pm

Originally Posted by gREgg-K
It isn't a piston seizure, is it?
I'm open to all possibilities, but it did run a month ago, during which time I rode less than 50 yards at low speed, and it died a quiet death rather than abruptly stopping. I wish I could remember if when I tried to start it a second time it was too difficult to turn over, like it is now, or if it just didn't start. But, I can't be sure.
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/15/19 12:46 am

Originally Posted by Magnetoman
Originally Posted by gREgg-K
It isn't a piston seizure, is it?
I'm open to all possibilities, but it did run a month ago, during which time I rode less than 50 yards at low speed, and it died a quiet death rather than abruptly stopping. I wish I could remember if when I tried to start it a second time it was too difficult to turn over, like it is now, or if it just didn't start. But, I can't be sure.

It's difficult to imagine a roller bearing engine tightening up due to a bearing lube failure, so I began to think of plain bearing surfaces. Piston skirts were the first thing to come to mind.
Now that I think more about it, how about the bush in the timing side support plate? Those are known to fail, and I've heard of them taking off the crank's feed stub during a failure.

.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/15/19 1:31 am

Originally Posted by gREgg-K
how about the bush in the timing side support plate? Those are known to fail, and I've heard of them taking off the crank's feed stub during a failure.
I hadn't heard of that problem, but a seized bush or two is consistent with the symptoms and would be (relatively) easy to check. Thanks very much for that suggestion. Any others?
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/15/19 3:32 am

Had a couple of seizures that happened just like you describe...the too-slow-idle-slow-death...problem was eventually traced to a small hole in the oil feeb line to the pump...sucking air...seized big-end..the bike had been running (at many 1000's rpm!) with the big-end cage melted, soldering the pin and rollers to the outer race, which ran as a plain bearing in the rod..

One thing is for sure: your engine is tight inside somewhere..
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/15/19 4:23 am

Originally Posted by Kerry W
the big-end cage melted, soldering the pin and rollers to the outer race,
Thanks for pointing out that possibility but, of course, I hope your're wrong and GreggK is right. If I do end up having to take the engine completely apart I'll be changing the 10:1 piston for something more suited to today's fuels. Conveniently, I have a Pearson crank assembly sitting on the shelf that I bought when the pound sank after the Brexit vote. I thought I was clever buying it then but little did I know the Brits were determined to do everything in their power to make the exchange rate even better.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/15/19 4:55 am

..every big-end seizure cloned has a silver-plated cage lining!
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/15/19 1:46 pm

Kerry has a good point: I recall a section in Golland's book entitled the "Development History of the Gold Star" discussing the measures BSA took to adequately lubricate the big end, and especially where the cage might rub. Their later efforts included "clocking" the oil feed holes in the pin relative to the crank position, and also adding feed holes in the pin to alleviate friction between the cage and the pin shoulders.

I too, hope my earlier suggestions prove correct, but Kerry may well have nailed it.

In any case, checking the simpler causes will be easy, and would be done "on the way in" to checking for a more serious defect in the big end.

.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/15/19 6:23 pm

Originally Posted by gREgg-K
how about the bush in the timing side support plate?
Originally Posted by Kerry W
seized big-end..
Of those two possibilities the answer turns out to be possibility #3 -- seized breather. Hallelujah, this looks like a 30 min. job at the cost of a gasket rather than several days and major dollars.

As the first photograph shows, when I pulled the timing cover off oil dripped from the crankshaft feed, so that was a good sign that oil had been flowing. Next I could rock each of the cam gears back and forth against the backlash, indicating they were free in their bushes. At that point I noticed flecks of Al near the magneto gear, as shown in the second photograph. I couldn't get the breather out of the timing case that I had left hanging from the cable, so I removed the tach drive and had to drift the breather out of the case using a socket. The third photograph shows the scoring of the cover caused by the seized breather.

And, yes, with the timing cover off the engine turns over without problem. I've never been so happy to find a seized part. If only I had a Sunnen hone... oh, wait, I do.


Attached picture Breather02.jpg
Attached picture Breather01.jpg
Attached picture Breather03.jpg
Attached picture Breather04.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/16/19 2:42 am

Excellent, if surprising result! Happy to be wrong! Jetting will be done by Sunday then!
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/16/19 4:08 am

Originally Posted by Kerry W
Happy to be wrong!
No one is happier than me. When I found the breather wouldn't rotate and then tried the kickstart lever, the clouds parted, the fog lifted, and a flock of songbirds appeared chirping with joy.
Posted By: hunter h

Re: Correct needle for 1000-series Concentrics? - 04/16/19 6:59 am

cheers that's good news . but looks like from your photos there is not any oil coming down from top end .The timing gears look dry in photos? hunter
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/16/19 12:59 pm

Oh happy day!

Now we have to answer the question: "Why did the breather seize in a timing chest which should have returning oil splashing around in it?" Is not enough oil coming into the chest, or is it being drained away too quickly, so that there is not enough oil for the timing gears to pick it up and distribute it upward?

I wonder if this failure has a cause similar to what results in the crank's oil feed stub seizing in the support plate bush?

.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/16/19 3:41 pm

Originally Posted by hunter h
looks like from your photos there is not any oil coming down from top end
Originally Posted by gREgg-K
Is not enough oil coming into the chest,
I'm reminded what my friend, whose shop burned down two weeks ago, says when asked what is the "best" oil to use -- "Any oil is way better than no oil." The seized breather illustrates this fact.

I hadn't run that bike in a long time so the cause could be simple, such as just taking longer than the ~30 sec. it ran to fill the cavities and wet the surfaces before oil could make it back to the timing chest. Or it could be more complex, such as having developed an air leak in the lines, or the oil pump has gone bad with time.

When I assembled it yesterday I used cam lube on the breather to keep it happy until oil takes over the job, but I will investigate the other possibilities today before I start the bike. And, once I do start it, I'll have the oil cap off so I can confirm that oil is returning to the tank before I peg the rev limiter.
Posted By: Gordo in Comox

Re: Correct needle for 1000-series Concentrics? - 04/16/19 5:06 pm

MM: Your adventure points to the whole area of splash/mist lubrication which I think is a major cause for engine start up wear. Most of us keenly pre-lube these areas when we build an engine but that is where it normally ends. One only needs to think of the pressure put onto a dry cam lobe and cam follower when cranking over an engine that has not run for a long time. Until the engine starts and oil starts to flow it will be metal to metal after a few kicks. Imagine the dry engine that took dozens or even hundreds of kicks to get going. Kicking will quickly pump oil into the crank but that will be about it. The GS will at least be pumping oil into the cam spindles but it will not immediately get to the lobes or other area needing splash or mist lubrication.

I always attempt to lubricate as much as possible before I start up a sleeping engine.

It varies from engine to engine but most have some easy way to get some oil trickling down towards the cams before starting. The A65 has the rocker cover for access, the Triumphs have the four rocker inspection caps, the unit singles have the two rocker inspection caps and the pre-unit BSA singles have either the tappet recess cover or rocker inspection cover. The later timed breather GS engines have either a cover or a tach drive that can be removed to access that area for a little pre-start lube. Most of the rockers covers I have seen have real wear in the area of the timed breather.

Gordo

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/16/19 8:11 pm

Originally Posted by Gordo in Comox
I always attempt to lubricate as much as possible before I start up a sleeping engine.
I knew that. But, if only I had acted on it. Sigh...

As the first photograph shows, the oil from the tank has to flow 750 miles (estimated) before it finally gets to the small pipe that leads to the rocker cover, then drip down to the timing chest, where it finally can lubricate the breather. It took me all of 15 minutes this morning to pump roughly a pint of oil everywhere in the rocker box that the stream from the oil can could reach, along with straight down the pushrod tunnel to the timing chest. This included removing the two bolts from the rocker feed and pumping oil directly into both rockers.

The 15 min. I "saved" by not doing what I "knew" I should have done resulted in unnecessary engine wear as well as much more than 15 min. of frustration spent trying to start an engine with a breather that seized because I hadn't taken the time to add the oil.

With that out of the way, I put fuel in the tank, the magneto on half-retard, tickled the carburetor, and it started immediately on the DocZ. Oil from the return line was flowing so I took a couple of laps of the driveway. Given that it wasn't fully warmed up and the driveway limited in what I could do, it feels like the slide cutaway could be correct. Also, when I tried to set the idle (again, not fully warmed up), I had to have the pilot screw almost all the way in so I'll switch from the #30 jet to a #25 when I get a chance.

The extra pint or so of oil I squirted into the engine today caused the oil tank to become too full (accentuated in the photograph by the bike being on its side stand) so I sucked 350 cc out. This makes the level lower than I originally had it but makes it easier to see oil squirting back from the return line. After I gain confidence in the oil pump I might add a bit of oil to the tank, but I might not.

Sadly, that's all the testing for today. My granddaughters got a new pony and they want to show it to us when they get out of school. I'm sorry to admit it to the true bike junkies, but jetting a Gold Star falls lower on the priority list than making my granddaughters happy.

Attached picture Breather05.jpg
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Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/16/19 8:22 pm

Originally Posted by Magnetoman
Originally Posted by Gordo in Comox
I always attempt to lubricate as much as possible before I start up a sleeping engine.
I knew that. But, if only I had acted on it. Sigh...
<SNIP>
The 15 min. I "saved" by not doing what I "knew" <SNIP>.

You're not alone of course, and it's so common that someone even came up with a saying to cover it:
"There's never enough time to do it right, but there's always time to do it over ..."

Sounds like you now have it under control. Congratulations MM, for wrestling the old beast to the ground!
.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/16/19 11:00 pm

Originally Posted by gREgg-K
"There's never enough time to do it right, but there's always time to do it over ..."
Sigh...
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/18/19 4:17 am

I did a short loop in the neighborhood this morning and the jetting seemed great (at least up to ~40 mph) so I decided to attach the air/fuel sensor and data logger. I proceeded slowly, trying to make sure nothing could fall off, or get caught in the spokes, so that took about 90 min. The photograph shows the final result.

Everything is held in place by nylon straps or zip ties, but I also used blue tape to keep a few things from wiggling. Starting from the back of the bike there's a sealed 12 V battery. Next is the inductive clamp around the spark plug lead for determining rpm. Located at the bend in the pipe is the wideband sensor. Clamped to the handlebars is the throttle position sensor based on a potentiometer and AA battery. And on top of the headlamp, along with all the extra wire, is the Innovate LM-1 and an accessory called the LMA-2 that accepts the input from the inductive clamp along with five 0-5 Volt channels. I'm only using one of the channels, for the throttle position sensor.

I started the bike, fired up the Innovate LM-1 (which takes ~30 sec. to warm the sensor), hit 'R'(ecord), and headed out on a planned ~10-mile loop. Unfortunately, I hadn't emptied the memory since I last used it and failed to see the brief message telling me it was full. Actually, I did see a message come up on the screen but didn't pay attention to it so I can't blame the unit.

The bike ran fairly well as I exited the neighborhood but the A/F readings were pretty low, i.e. rich. I didn't pay a lot of attention to the numbers (but they were often in the 11s and 12s, and almost never hit 14) since it all was, ahem, being recorded for later viewing. When I returned to the neighborhood I was behind a car going slowly and the bike started loading up. I was afraid it would die on me so I reved the engine to get it running well and passed the guy on a blind curve going maybe 20 mph at 4000 rpm. I'm sure he rightfully was swearing at me for being such a [***].

I made it back home and up the steep driveway only to discover when I was back under the carport that there was no flashing 'R' in the display to indicate it was recording. So, the DocZ started the bike again but I didn't get any further than the gate before it was 8-stroking at anything other than idle. That ended the day.

The current configuration is:
-- 30 pilot
-- .106 needle jet (measured 0.1065"-0.1066")
-- 4-stroke needle on top notch
-- 2-stroke spray tube
-- cutaway #3
-- 340 main

Since the richness is most pronounced at low throttle settings I'll change to a 25 pilot in the morning and hope that makes a big difference. Dropping the needle isn't an option since it's already on the top notch. Now that I've cleared the LM-1's memory tomorrow's run should be more enlightening than today's.


Attached picture InnovateAF.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/19/19 10:37 pm

A mini heat wave already had us at 96 oF at 1pm and it's now 3:30 pm and 98 oF so I only was able to make one ride today. OK, I could make more, but did I mention it's 98 oF?

A few notes in reading the attached two graphs from my data logger. The values for AFR (magenta), rpm (black), and voltage from the throttle position sensor (red) at the upper right are from the time into today's run (11 min. 29.33 sec. for the first graph) where I had the cursor set when I took the screen shot. The rpm values shown in black are 2x what they should be, apparently because the inductive clamp I have laying directly on the magneto is picking up a signal from there as well as the wire. The voltage values are 1.5/5.0 of what they should be because I incorrectly tricked the program when it imported the data -- I should have used a factor of 5.0/1.5. The appropriate scales for these three quantities are shown in the same colors on the Y axis. As background, the stoichiometric ration for old fashioned gasoline is 14.7, and maximum power from most engines obtained around 12-13.

Referring to the first graph, during the interval between 11:22 and 11:48 it can be seen that I had the throttle at a fairly constant ~0.1 so it was mostly running on the pilot circuit. The AFR can be seen to have been a very rich 11 or so. The four sharp spikes in this time interval are because the engine missed, allowing raw fuel and oxygen to pass through to the exhaust. Engine rpm was ~7800/2 = 3900 so each combustion cycle was (3900/2)-1 = 0.5 msec. The fact these spikes are seen tells us the response time of the sensor is at least this fast.

The three regions near 11:12, 11:20 and 11:52 show that when I completely rolled off the throttle the exhaust mixture got very lean because only air and a little unburned fuel was passing through under that circumstance.

Turning to the second graph, I had the cursor placed at 8 min. 19.3 sec. for the screen shot, at which point the throttle was wide open. Note that the AFR is a very rich 9.35.

Starting at the far left of this graph it can be seen that over a time of ~1¾ sec. I increased it to ~½ throttle. Up to ~¼ throttle the AFR stayed around 13, but then started dropping as the throttle opened wider, dropping to ~10. I briefly let off the throttle, then rolled it back on to full throttle. Again up to partial throttle the AFR went back to ~13, but again it dropped to below 10 by full throttle. Note that these are "transient" behaviors, not steady state, so there's a lag between changing the throttle position and the engine catching up with the change.

It's not worthwhile analyzing this data any further. The bike was very rich and, as a result, it would load up at low throttle settings and I'd have to rev the engine to clean it out enough that it would again run smoothly. So, there's a lot of bad behavior reflected in various time intervals.

This morning I replaced the #30 pilot with a #25 but did not adjust it before today's run for reasons not worth going into. Had it been adjusted I assume the AFR at low throttle settings would have been more reasonable than the super-rich <10 that caused the bike to load up today. I'll drop the main jet by a couple of sizes and adjust the idle mixture before setting off on a similar run tomorrow.


Attached picture Innovate01.jpg
Attached picture Innovate02.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/20/19 6:34 pm

I made some progress on my jetting this morning. I found that turning the pilot mixture screw all the way in had no effect on the rpm. The last time I had that problem, coincidentally on a Gold Star but with a Monobloc, I found the float level was very low. So, although I checked it long ago, after lunch I'll check the float level again.

With the pilot screw all the way in I made another 8-mile run. Halfway through the run, when the engine was fully up to temperature, I stopped and watched the AFR as I adjusted the pilot screw. It got richer as I backed it out a half turn, and got leaner as I turned it back in, so all the way in was leaner than yesterday (but still not correct). Anyway, with the somewhat leaner pilot mixture the bike behaved better than yesterday. The mixture was still too rich but it never dropped below 10 where igniting it seems to be problematic.

The DocZ rollers are earning their keep. Bikes like rich mixtures to start but my Amal 1036 doesn't have a choke (the cap only has a hole for the throttle cable and thus far I haven't located the appropriate 1000-series cap). But, no choke is no problem with rollers. One problem I am having, though, is I'm way too used to the up-for-down shift pattern of my other Gold Stars. This one has rear sets, but not a reverse cam plate, so it has a Triumph-like up-for-up shift pattern. I have a reverse cam plate I could install but I'm not sufficiently motivated (or, the least bit motivated) to do so.
Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 04/20/19 7:00 pm

Have you got a 105 needle jet to try?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/20/19 7:07 pm

Originally Posted by koncretekid
Have you got a 105 needle jet to try?
Indeed I do. It certainly could be that the additional suction power of the 2-stroke body will require a smaller needle jet. But, one thing at a time. First I have to deal with the pilot circuit and possible issue with the fuel level.
Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 04/20/19 7:25 pm

MM would you like a 4 stroke (straight) spray tube?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/20/19 8:31 pm

Originally Posted by John Healy
MM would you like a 4 stroke (straight) spray tube?
John, thank you very much for the generous offer. However, I made a drift and pressed one out of an old body a few weeks ago. But, in the interests of science, and motivated by my flow bench testing, I decided to see how well I could do with the 2-stroke spray tube and with the 2-stroke constriction in the air correction passage. If I can't wrestle it into submission with this configuration I'll convert it to fully 4-stroke.

Originally Posted by Magnetoman
The last time I had that problem, ... I found the float level was very low.
The float is supposed to be 0.060"-0.080" below the top surface of the bowl. Do you suppose it's close enough now?

It's interesting that this bike, as well as the Catalina that previously had the same problem with its Monobloc, ran at all, let alone not horribly, with the fuel level fully 1" below where it's supposed to be. All I did before taking the photograph was drain the bowl as a result of switching plugs at the bottom, then turn the petcocks on. Tapping the bowl with a screwdriver handle didn't cause the level to change. It's easy to image the float hanging up on something as the bowl filled, causing the needle not to seat and therefore to overflow. But, how it can stop the flow where it did is a puzzle, especially since at some point in the past it was fine when I did the same test on the bench. However, since then the bowl has been off several time. The carburetor will now come off the bike for close inspection and repair. This "discovery" counts as significant progress.

Addendum: actually, the top of the float is supposed to be ~0.080" below the top of the bowl, but I can't seem to find any description of where the fuel level is supposed to be. John?...
I'm not saying I made the following mistake, but I'm not saying I didn't, either. By the time I got the float bowl into the garage and looked at it the tang on the float was above the needle. If this is how it was when it was in the carburetor it would have stopped the flow too soon, resulting in a too-low level. After carefully checking the height when the tang, not the end of the needle, was depressed I re-installed it and the second photograph shows where the fuel is now. Still, where should the level be?

p.s. The new, higher fuel level made somewhat of a difference, although it still idles best with the pilot mixture screw turned all the way in (#25 pilot jet). If I back the screw out 1/2 turn the idle drops to where I fear it could die. I could change to a #20 but first I'd really, really like to know where the fuel level should be.

p.p.s. I found a couple of references that say the fuel level should be 4.5-6 mm below the top of the float bowl. Assuming this is correct (¿is it?), my fuel level is still too low at ~10 mm below the top of the float bowl in the center, i.e. in the middle of the jets.


Attached picture FloatLevel.jpg
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Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 04/20/19 10:47 pm

Wouldn't the important level be at the inlet to the main jet, as the carb is not level? And if the level was too low, how would it cause a rich condition?
Tom
Posted By: chaterlea25

Re: Correct needle for 1000-series Concentrics? - 04/20/19 11:01 pm

Hi MM.
Quote
I stopped and watched the AFR as I adjusted the pilot screw. It got richer as I backed it out a half turn, and got leaner as I turned it back in,


This is 100% the opposite of what should happen ????
Opening the air screw should lean the mixture
in an earlier post you also said the opposite of what is correct on selecting pilot jet size. ??
Carbs in general that behave like this usually have blocked internal passages, the two tiny drillings one under the engine side of the slide and the other further inwards
I am presuming the 1000 series did not have the pressed in pilot bush as on other Concentrics? adding a screwed in pilot to one of those really
messes things up
The Concentrics also do not like being mounted at a downdraft angle this makes setting the fuel level a matter of trial and error to find the best results,
The factory level recommendations are for horizontally mounted carbs
Set at the factory level the pilot circuit floods when the carb is tilted forwards
As a base guide I would aim to set the fuel level to the bottom edge of the thread of the pilot air screw

Which Sunday did You say ?????
John




Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 04/20/19 11:08 pm

When the body is level it is .170" to .240" below top edge. With the MKII there are considerations about the location of the pilot jet when the body angle is more than 15°. Have had little experience with this carb. They move it from the outlet side to the inlet side.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/21/19 12:38 am

Originally Posted by koncretekid
Wouldn't the important level be at the inlet to the main jet, as the carb is not level? And if the level was too low, how would it cause a rich condition?
What matters is the height of the fuel below the spray tube, inside the jet chamber. Even if the main jet were mounted at 45-deg. so its inlet were higher than it normally would be, all that matters is the height of the fuel inside the jet chamber, not at the submerged inlet to the main jet.

As for whether it should be too rich or too lean when the fuel level is too low, it is behaving in the same way the Monobloc on my Catalina behaved a year ago when the fuel level in the float bowl was much too low, i.e. it was nearly unresponsive to the pilot mixture screw but ran best with the screw all the way in.

Note that after I managed to raise the level to the current ~10 mm the engine started to actually respond to the pilot mixture screw, whereas before it didn't (I could see the AFR change a little but the effect on the running was quite a bit less than it is now).

Originally Posted by chaterlea25
Quote
I stopped and watched the AFR as I adjusted the pilot screw. It got richer as I backed it out a half turn, and got leaner as I turned it back in,
This is 100% the opposite of what should happen ????
Opening the air screw should lean the mixture
Yes, that's certainly true when the fuel level in the bowl is close to correct. Which it isn't. As I wrote above, whether or not it should have acted this way, this is also how the Monobloc on the Catalina behaved when its fuel level was very low.

Originally Posted by chaterlea25
Carbs in general that behave like this usually have blocked internal passages, ...
I am presuming the 1000 series did not have the pressed in pilot bush as on other Concentrics?
The Concentrics also do not like being mounted at a downdraft angle this makes setting the fuel level a matter of trial and error to find the best results,
The factory level recommendations are for horizontally mounted carbs
Set at the factory level the pilot circuit floods when the carb is tilted forwards
As a base guide I would aim to set the fuel level to the bottom edge of the thread of the pilot air screw
This is a 2-stroke carburetor so has the replaceable pilot jet. However, the pilot circuit draws from the bottom of the bowl, and the jet is surrounded by the float bowl gasket so fuel only can get to it from the bottom of the bowl, and anyway as the photographs in my previous post show, the fuel level is too low to reach the gasket even though there is a downdraft angle.

I think the bottom of the of the pilot air screw would be way too high. If you think it is flooding now, it really would flood then. I'm going for the factory-recommended 4.5-6 mm (John's 0.170" - 0.240"). Unfortunately, all I have at the moment are a few original (non-adjustable) floats. I know the level can be tweaked by pressing on the needle seat, but even with a float in it that comes to the top of the float bowl the level is still ~10 mm too low so pushing the seat lower would result in the float topping out and the needle not sealing. I've ordered an adjustable "stay-up" float but it won't be here until the middle of the week.

Originally Posted by chaterlea25
Which Sunday did You say ?????
If the 'Competition' is fully resurrected tomorrow it will be an Easter Miracle.

Originally Posted by John Healy
When the body is level it is .170" to .240" below top edge.
Thanks for that. That's what I'll set when the adjustable float arrives.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/21/19 11:25 am

Reference the comment above about 2 stroke Concentrics having replaceable pilot jets, my experience is that the 1000 series ALL had replaceable pilot jets.

Also, I've never seen a 1000 series Concentric top that had a hole for the choke cable, nor a slide with the hole for the choke slide, but that's just me.
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 04/21/19 11:55 am

I have a decent collection of 1000 series carbs and parts ranging from 1034 to 1038. None of the slides or tops have any provision for a choke. I have never seen any 1000 series or parts with choke provision.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/21/19 2:30 pm

Originally Posted by Kerry W
I've never seen a 1000 series Concentric top that had a hole for the choke cable,
Originally Posted by Rich B
I have never seen any 1000 series or parts with choke provision.
Prompted by your comments I looked more closely at the parts list. Only the top with a single hole was supplied for the 1000 so my search was bound to be lengthy. Series 1000s were supplied for a few four strokes at the time which is why I (incorrectly) thought chokes might be available, although scarce.
Posted By: hunter h

Re: Correct needle for 1000-series Concentrics? - 04/21/19 3:05 pm

cheers I was just looking at the 1038 on a GS the I have on Fri and was thinking the same thing . poss a top could be made but what about the slide ? they were not made to be used with choke. h
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/21/19 3:29 pm

My carburetor starting ritual with the 930 Concentric on the BB is tickle and full choke, with the choke removed immediately after it starts. However, with the 1-5/32" Monobloc on the Catalina it's no tickle and no choke. So, maybe the Competition will be just as easy to start without a choke as it would be if it could have one.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/21/19 4:29 pm

Just a thought, what type of float needle are you using?
The brass/viton type often results in a lower fuel level.
Amal recommend their newer alloy/viton needle to avoid this issue, and I can vouch for the difference.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/21/19 4:49 pm

Originally Posted by koan58
Just a thought, what type of float needle are you using?
I'm using alloy/Viton. I currently only have three floats in my Concentric box, all the original plastic. I suspect the problem is that all of them probably have warped with the passing of nearly 50 years and, thanks to the leverage, it doesn't take much change in the projection that operates the needle to change the fuel height by quite a bit. As I wrote in a previous post the current configuration of the float is such that even if I pressed the seat down in an attempt to raise the fuel level it wouldn't help because the floats would top out on the carburetor body.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 04/21/19 9:07 pm

You could add weight to the float, that will raise the fuel level.
Just exactly how , I dunno, never done it, whatever glue is fuel resistant and a short bit of cable tie maybe?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/22/19 1:05 am

Originally Posted by gavin eisler
You could add weight to the float, that will raise the fuel level.
Amal didn't leave much empty space in the float chamber, and even if some Pb did fit, messing around to find the right weight would be a headache. More so when the weight fell off and jammed the needle open. I think it's best for the adjustable stay-up float to arrive.

It's probably worth repeating that the pilot circuit is a completely separate "carburetor" from the main circuit, with both "carburetors" contributing in different proportions as a function of slide opening. The first photograph is a bottom-up view of a partially sectioned 627 Amal from a Sherpa T that gave its body to science. Air is in green and fuel is in red. The remnants of the threads at the bottom show where the pilot mixture screw goes.

Originally Posted by chaterlea25
Opening the air screw should lean the mixture
As can be seen, opening the air screw does let more air flow through that passage, but the effect of that screw on the mixture isn't just a straightforward diluting of the fuel with the extra air. To find out more, it was back to the flow bench.

The second photograph shows that I drilled out a longer Monobloc screw and turned it down to fit a line to the manometer. I sealed it with grease on the threads. Although the inside of the bowl itself, other than the volume in the jet block, should stay at atmospheric pressure due to air leaks, I set up my manometer for a differential measurement anyway. It turns out that it did stay close to atmospheric pressure up to ~3/4 throttle , but then dropped in pressure as the flow increased to full throttle. Although I expect the amount of depression in the float bowl, and hence the effect on the flow of the pilot jet, would vary between carburetors, I'll show below that the effect of this on the mixture would be negligible.

The third image shows the results of my measurements of the pressure drop inside the pilot circuit with the air inlet at the front of the carburetor blocked and with the pilot jet blocked (top curve) and open (bottom curve). The data was taken at the same 7" H20 as the other curves on this graph paper.

The measured depression is a result of the air flow over the two tiny holes at the engine side of the slide (seen in the first photograph). In the case of the bottom curve this is partially offset by air flowing from the carburetor bowl through the pilot jet. However, the greater depression of the top curve corresponds to actual operation because fuel in the bowl would not allow air to flow through the pilot jet. As can be seen, at 5 CFM (~1/8 throttle) the depression over the pilot jet is 3.06x greater than that over the needle jet.

A #25 pilot jet has diameter 0.0175" for an area of 2.40x10-4 sq.in. The annular area of a 0.1065" needle jet with a 0.0984" needle is 13.0x10-4 sq.in., which is 5.4x greater. What this means is that at ~1/8 throttle, where Amal's simplified tuning description says the pilot jet is only just losing its influence, already the main circuit is supplying 5.4x/3.06x = ~1.75x more fuel than the pilot circuit.

The fourth image shows the depression in the pilot circuit at higher flows. As can be seen it saturates at ~0.150 psi whereas that of the spray tube of a 2-stroke body (dashed blue/red curve) continues increasing to 0.340 psi at full throttle. Further, by that point the needle is essentially out of the needle jet and flow out the spray tube is determined by the main jet. Assuming a #300 main jet (dia. 0.059"; area =27.3 x10-4 sq.in) the relative flow through the spray tube will be greater by (27.3 x10-4 / 2.40 x10-4) x (0.340 psi / 0.140 psi) = 27.7x. That's a pretty large factor, but it shows the pilot circuit is still responsible for nearly 4% of the fuel supply even at full throttle.

Finally, ending on the point I originally intended to make with this post, what this information shows is that opening the pilot "air screw" simultaneously does two things that alter the mixture. It dilutes the fuel with air from the pilot air passage, but it also lowers the depression so less fuel is drawn into the circuit. That is, turning the screw CCW adds air while also subtracting fuel. Figuring out the relative magnitudes of the two effects is left as an exercise for the reader.


Attached picture Pilot01.jpg
Attached picture Pilot02.jpg
Attached picture Pilot03.jpg
Attached picture Pilot04.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/22/19 3:05 am

That backs up what I have seen on the dyno in the past, where my 'dyno guy' (a pretty smart operator) altered top end power/air:fuel on a small 2 stroke single with a small tweak of the air screw, not affecting low end function.

Thanks
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/22/19 7:37 pm

The front to back asymmetry of the horseshoe shaped float in the concentric results in greater sensitivity to downdraft angle (as say compared to the floats in a monobloc).

The concentric float (with its horseshoe shape) has a large buoyancy bias toward the engine side, so any leaning in that direction will close the float needle at a lower average fuel level than that advised by Amal.

On my more modestly sloping carbs (pre-unit T120) I settled at a fuel level of 8mm static and level on the bench, with stayup floats. Attempts at any higher just resulted in flooding/dripping carbs when installed (the stayups tend to be nearer the top limit of movement than the plastic floats).

It is possible that you may have to accept a compromise of fuel level, and tune from there.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/22/19 10:28 pm

Originally Posted by koan58
Attempts at any higher just resulted in flooding/dripping carbs when installed.
The first photograph shows that as installed on the Gold Star the tilt is ~14-15 degrees. The second photograph shows the carburetor rotated by 15 degrees overlaid with a band of width 1.8 mm based on John Healy's figures of .170" to .240" (4.3-6.1 mm). Note that if the fuel level is set at the high end of this range (i.e. the bottom edge of the green band) it will just touch the outer edge of the gasket (the inner edge would be slightly above sea level).

From my previous post it can be seen that the float bowl gasket doesn't just have to stop gasoline from leaking out, it has to stop air from leaking in. At least around the pilot jet where it would affect the pilot circuit. As long as they're undamaged red fiber gaskets do a good job of stopping gasoline but once I get the float adjusted to the proper level I'll use Permatex Permashield gasket dressing to seal it ("this compound resists common engine fluids, including oil, gasoline, ethanol,...").

The third photograph shows that the carburetor is mounted on the test stand awaiting arrival of the adjustable float.


Attached picture Floatlevel4.jpg
Attached picture Floatlevel7.jpg
Attached picture Floatlevel6.jpg
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/22/19 11:09 pm

I would recommend satisfying yourself that the "manometer style" technique accurately accords with a bench measurement of fuel level in the centre of the bowl.
As with any other measurement, it should be checked against a reliable standard.
I did this, and reported my findings several years ago. I was using a similar diameter (1/4") tube and found a 2+mm discrepancy between tube and actual level in the bowl.

Perhaps I failed to explain my reasoning clearly, but the design of the float means there is more fluid displacement when the carb is tilted in a down draft direction, hence earlier closure of the float valve, compared to a horizontal situation.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/23/19 12:53 am

Originally Posted by koan58
I would recommend satisfying yourself that the "manometer style" technique accurately accords with a bench measurement of fuel level in the centre of the bowl.
Perhaps I failed to explain my reasoning clearly,...
If someone fails the eye test they have to give up their license to drive. If I physicist fails the meniscus-reading manometer test, they have to give up their license to practice physics.

I understand the issue you mentioned. That's why the fuel level has to be measured on the center line, but the carburetor has to be mounted at 15-deg.
Posted By: Jerry Roy

Re: Correct needle for 1000-series Concentrics? - 04/23/19 10:47 am

Originally Posted by Magnetoman

I understand the issue you mentioned. That's why the fuel level has to be measured on the center line, but the carburetor has to be mounted at 15-deg.



Could trigonometry be used to decide how much higher the fuel level should be on the downhill side of the bowl?
Or do we leave that to the mathematicians? laughing clap

JR
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/23/19 5:16 pm

Originally Posted by Jerry Roy
Could trigonometry be used to decide how much higher the fuel level should be on the downhill side of the bowl?
As the photograph shows the distance from the center of the bowl to the edge that will be lowest when the carburetor is tilted is 20 mm. Two ways of inflicting trigonometry on this problem are:

1) The maximum angle the carburetor can be tilted if the fuel is to just reach that edge if the fuel is 4.3-6.1 mm below the lip at the center is:

θ = sin-1( 4.3 / 20) - sin-1(6.1 / 20) = 12.4° - 17.8°

or,

2) The minimum depth that the fuel can be at the center if it is to just reach the edge of the bowl when the angle is 15° is 20 mm x sin15° = 5.2 mm.

I measured the angle to be ~14-15° so 15° would be worst case (if I measured correctly). This means if I aim for 5.5 mm, which is within the acceptable range, the fuel never will even touch the gasket. Unless the engine shakes which, of course, none of them do.

Originally Posted by koan58
the "manometer style" technique ... should be checked against a reliable standard.
I'm puzzled by what you mean by this. I can't even imagine what a "reliable standard" for this would look like since the height of the meniscus only depends on the gravitational constant being the same at both ends of the manometer. Since the two ends of the tube are only a horizontal distance of ~2 cm apart even a block of kryptonite under the float bowl wouldn't affect my measurement.


Attached picture FloatLevel9.jpg
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/23/19 8:32 pm

Originally Posted by koan58
[the "manometer style" technique ... should be checked against a reliable standard.]

Originally Posted by Magnetoman
[I'm puzzled by what you mean by this. I can't even imagine what a "reliable standard" for this would look like since the height of the meniscus only depends on the gravitational constant being the same at both ends of the manometer. Since the two ends of the tube are only a horizontal distance of ~2 cm apart even a block of kryptonite under the float bowl wouldn't affect my measurement.]

Well you did ask...

It should be remembered that we only use the term "manometer type tube" very loosely for descriptive brevity. It is in no way a manometer, it is merely a level tube.

When I got my stayup floats and alloy needles, I decided to conduct a more thorough examination than I had previously done of what was going on in the float bowl with both the old and new components in different combinations.
The "old components" were standard, not very old plastic floats and brass/viton needles.
The "new components" were stayup floats and alloy/viton needles.
I was also interested to see what difference just changing to the alloy/viton needles made with the old type floats.
This was inspired by a post from a contributor (Caulky) who had taken a preliminary look at the functioning of brass/viton needles in concentrics, and the impact on fuel level, and also that I had never been fully satisfied with the performance of my original setup, in terms of a dependable idle, engine temperature and subtle lack of smoothness in general running when compared with pals who ran monoblocs on similar engines (pre-unit T120).

I started out thinking to use the convenience of the "manometer type" method, plumbed into the drain plug similar to yours, with the carbs in situ (the only extra convenience being that it was T'd with a clamped pipe for easy draining/refilling of the bowl for repeated measurements).
I began with std float and brass needle, with a sight tube being the small gauge tube from a battery breather. I found fuel level indications (on repeated drainings/refillings) varying by several mm, though all were well below Amal specs.
I then tried the largest ID transparent tube I had available (1/4"), and still found several mm variation, and if anything the avarage level seemed slightly lower.

At this stage I took the bowl to the bench vice, carefully levelled, with the 1/4" manometer tube and jury-rigged fuel tank. Using a bridge across the bowl surface I could dip the depth gauge of my vernier into the centre of the bowl to determine the actual fuel level depth, and compare with what I saw in the tube, over multiple refills.
What I found was that the directly measured depth varied little (not even a whole mm range), the tube exhibited 2X to 3X this range. Perhaps more significantly, the average tube measurement was ~2+ mm higher fuel level than the direct measurement.

This is what I meant by a "reliable standard" with which to compare the accuracy of your tube. Perhaps I should have said "reality standard", which requires no kryptonite, just a measuring stick to calibrate your tube.
In any other measurement you make, you go to proper lengths to establish that your technique accords with a more defined reality standard.
I see a couple of reasons beyond a black hole hidden under your workshop why the tube measurement may differ and vary more, compared with a direct measurement.

1) Capillary action. The attraction between the fuel and the tube not only results in the meniscus, it also produces an upward force raising the fuel level in the tube. That there is a concave meniscus in the first place illustrates that the molecular forces are acting in this direction. Assuming all other factors are equal, the smaller the ID of the tube, the more this capillary raising of level, and even 1/4" ID has a significant effect.
This is for water in glass, for illustration of the principle only:
https://en.wikipedia.org/wiki/Capillary_action#/media/File:2014.06.17_Water_height_capillary.jpg

The other end of the tube is inside the float chamber, with 30+mm diameter at its meniscus. The capillary force here is insignificant in comparison.

2) Wetting effect of fuel on the inside surface of the tube. After repeated tests the tube has a film of fuel molecules adhering to its inside surface, above where the meniscus would usually settle. This then results in the angle of contact between meniscus and tube being closer to vertical, the fuel level in the tube rising in consequence.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 04/23/19 8:42 pm

"It should be remembered that we only use the term "manometer type tube" very loosely for descriptive brevity. It is in no way a manometer, it is merely a level tube."

Where Im from we call it a sight glass. Very often static level is different from running level, particularly if there is a
swirl in the housing. Not really applicable to carbs, but the capillary action thing is a good point.

otherwise very interesting so far. MMs results on the pilot system were not what I expected. just goes to show.
Surely the float bowl bleeds air through the tickler, doesnt just rely on leaks ( although the tickler is just a controlled leak).
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/23/19 9:36 pm

Gavin, I don't think that the tickler is a controlled leak, it is just a passage for balancing bowl to atmosphere, a breather.
It doesn't need to do much at all, because fuel taken by the engine is replaced by fuel delivered from the tank.
All of the "vacuums" happen above, away from the bowl.

Running level must be slightly lower than static level, otherwise there'd be no opening of the valve for fuel, to replace that being used by the engine.
As the fuel only flows through the float valve under gravity, it's flow can only be according to the needle's lift from the seat. Hence for high flow at high rpm/throttle the float must be lower than at idle. This can only happen by the fuel level being lower than at idle.

This says to me that one can only hope to establish fuel level in one standard set of circumstances (which is what Amal advise) and tune from there. That there are numerous varied applications of one simple carb illustrates how tolerant/versatile it is.

For maybe 20 years I'd put up with the brass needles, unaware that the fuel level was ~8mm lower than it should be.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 04/23/19 11:07 pm

"I don't think that the tickler is a controlled leak", OK,
"For maybe 20 years I'd put up with the brass needles, unaware that the fuel level was ~8mm lower than it should be"

Same here, . Fuel height is overrated. Fun though..
Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 04/23/19 11:27 pm

Quote
"For maybe 20 years I'd put up with the brass needles, unaware that the fuel level was ~8mm lower than it should be"


There is only one answer to this statement... No! 0.300" +-????

The aluminum needle followed the introduction of the Stay-Up float. The action of the Stay-Up float doesn't naturally unseat the needle. Thus the search for a lighter needle so the head of fuel unseats the needle instead of the the float. It is to correct a problem that wasn't there with the plastic float.

[quote]As the fuel only flows through the float valve under gravity,[]quote]

A problem that wasn't a problem with the plastic float as the tangs on the float raised the needle when the bowl needs fuel, especially when float level was done by moving the needle seat. While the action of the Stay-Up float barely lifts the needle as design, bending the tangs to set the float level makes things worse. The float can fall and the tangs never lift the needle. It can be made right! Koan look closely at what is happening.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/24/19 12:15 am

I expected you to pipe in John at some stage, to defend the use of brass needles in the Concentric.
We have been through this in previous discussions. The concentric was designed to work with a very light float needle (a 0.3g plasic one), because of its unconventional arrangement of the needle being able to close the valve under its own weight (which the brass one is able to do). Alloy is 0.5g, Brass is 1.5g.

The only way the carb float bowl system functions as originally designed is by using either the original plastic or the newer alloy needle, only with the heavy brass needle does the weight of the falling float have to open the valve, rather than properly for the float bouyancy to close the valve.
This makes a more than 5mm difference in fuel level drop before the float intervenes to lift the needle, due to the freedom of the float tangs within the needle space.
It is laughable that a cistern ballcock type of arrangement depends on the weight of the needle to stop the valve, it is always closed by positive force from the ballcock, and always opened by fluid pressure when the ballcock drops a little, the ballcock doesn't have to pull the valve open.

Respectfully, I question which of us needs to look more closely.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/24/19 2:23 am

From the Amal site itself:
http://amalcarb.co.uk/optimising-mark-1-concentric-fuel-levels

If your float chamber is fitted with a brass needle valve, you may find the valve sealing under its own weight, before the float has risen far enough to press it shut. Symptoms of this problem can be that the carburetter takes a long time to tickle, hesitates on pickup and does not idle reliably. A Viton tipped aluminium needle valve is now available that overcomes this problem. It is now fitted as standard equipment to all new Mark 1 Concentric carburetters.

No mention of "if you have stayup floats", it is clearly talking of the issue of brass needles.
Indeed, when I installed my alloy needles in the experiment I described earlier, I found an immediate rise of fuel level of 6-8mm straight away, using just the plastic floats, as compared with the brass needles.
I ended up settling at that fuel level with the stayup floats (I settled at 8mm fuel level) because even with the adjustability of the stayup floats there are constraints, one being that they tend to float a bit higher and abut the bottom of the body a bit sooner than the old plastic floats. It was a transformation of the behaviour of the engine.
----------------------------------------------------------------------------------------------------------------
For anybody who isn't bored enough with my tale already, I'll try to kill you off with my original postings from 2014:
MkI concentric float needle/stayup float

Hi folks, this follows earlier posts by Caulky et al about fuel level in MkI concentric carbs vs various types of float/needles, which inspired me to explore.
New 930 MkI concentric carbs on 8-stud T120.
I've used the brass/viton needles since the mid 80's, and I've always felt the bike ran differently from time to time, subtle but feelable.
Got upgrade kits, including Stayup float and alloy float needle.
Began by making manometer of 4mm ID plastic tube into plastic floatbowl plug, cabletied to side of bowl.
Then began measuring fuel levels of carbs on the bike, found this a bit vague, carbs lean toward head, meniscus, parallax etc, so averages of multiple measurements. 2 gal fuel in tank.
Original plastic float/brass needle 13.5mm
Swapping to alloy needle/original plastic float 8.5mm
Swapping to Stayup float/alloy needle 8.5mm
So just changing from brass to alloy needles brings fuel level 5mm closer to spec.
Decided to study the bowls on the bench, used 20cm head of fuel, Stayups & alloy needles.
Had the manometer pipe connected to compare with direct measurement. Bowl levelled.
Started by dropping a vernier down between float toe/bowl, found this unreliable, think surface tension between the 2 close surfaces raises the apparent level.
So made a bridge of known height to measure down into the centre of the bowl, gotta be the truest measure?
Right was 8mm (the nicest pot), left 9+mm
Set left to 8mm as well.
Went on 40ml run, felt like "on agood day" had to open airscrews 1/4 to 1/3 turn, steady idling.
Will need more rides to see if not good days still happen.
This idea of the brass float needle closing the fuel off under its own weight(not from pressure from the float) is absolutely confirmed. Changing brass to alloy(1.5g-0.5g) raised fuel 5mm, which corresponds to float toe movement within the free tang space of the needle. When filling the header pipe to the test bowl I would initially see fuel freely passing needle(float fully down pulling needle fully open) float would rise part way (where the tangs just allow needle to seal its seat) and settle until header pipe reaches ~15cm.
At this head the alloy needle rattles up and down, letting fuel through to a level which is constant for heads 15cm upwards. My tank running low is about 20cm head.
My own calcs said alloy needle would take 9.5cm head, a bit more actually needed to overcome stiction maybe?
For brass needles I calc a petrol head of 37cm(over the top of most petrol tanks) is needed to unseat them against their weight, so they will always give toward a 5mm lower fuel level.
Why did I choose 8mm fuel level? Bit of a punt really, the original plastic float/alloy needle gave ~7mm and I figured its been working pretty well for decades on up to 5mm lower. Amal spec 6.35mm max, some good sources have suggested 7.35mm, so I went 8.
Phew Dave

then someone replied:

I have brass needles and nylon floats in a pair of Concentrics I just bolted onto my '66 T120R as part of a troubleshooting exercise. I have wondered about setting up those needles in my drill press and drilling them across their axis to reduce their weight. Might give it a try one of these days and compare it to your alloy weight

my response:

Glad you found it interesting Rob!
This post was only the headlines, along the way were many other subtle observations/realisations:-
Original nylon needles are 0.3g, alloy 0.5g, brass 1.5g
but weight isn't the whole story, approx densities of materials:-
nylon 1.7, alloy 2.7, brass 8.5
The needle has a certain bouyancy in its fuel-filled housing (density of petrol~0.74) which reduces the effective weight that has to be overcome by the fuel head to open.
The impact of this is tiny on brass needles (8.5 minus 0.74 effective density) but is significant on nylon & alloy needles (1.7-0.74 and 2.7-0.74 respectively).
Drilling out brass needles to 0.5g (if possible to remove 2/3 of the brass?) will greatly reduce head required, but not as much as replacing with alloy needles, because that 0.5g of brass will feel almost no benefit from its bouyancy in petrol. I wouldn't waste the time when the alloys are cheap.
My calculated minimum fuel heads required (bouyancy allowed for):-
nylon 4.7cm, alloy 9.5cm, brass 37cm.
Another benefit of the alloy needle is its upper float tang mushroom is 1.5mm above the lower tang flange(as compared to brass needle 1.7mm). Tangs are 0.7mm thick, so the float dropping as fuel level falls lifts the alloy needle sooner/further.
I find tickling now a 2-3 sec affair, compared to say 10 sec with brass. This is because the tickler had to actually lift the needle from the seat, so only opening valve a little, whereas the alloy voluntarily lifts the full distance allowed by the float tangs, opening the valve much more.
I found using the manometer tube problematic, not very repeatable and hard to judge level, would probably be improved by using a bigger ID and glass tube.
However I found direct measurement on the bench at centre of bowl to be convincingly reliable. Dave
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/24/19 4:53 am

OK, more misinformation has been posted here than I care to address. So, I won't. Either take my word for it that it is possible to read a manometer to better than 0.1 mm. Or don't. It's also possible to misread a manometer if you don't know how to correctly measure a meniscus. As an example of what is possible, if you needed to determine the temperature of liquid helium to 0.001 K near 1.5 K you would need to accurately read a manometer to 0.02 mm, as I have routinely done (using a cathetometer). Again, take my word for it or don't. But, if I don't address other posts don't assume that means I think the information in those posts is necessarily correct.

Originally Posted by gavin eisler
but the capillary action thing is a good point.
Not for a tube has a ~1/4" ID.

Originally Posted by gavin eisler
Surely the float bowl bleeds air through the tickler, doesnt just rely on leaks ( although the tickler is just a controlled leak).
Air does bleed in through the tickler, but in the carburetor I tested that leak/bleed wasn't fast enough to keep up with the pressure drop once the air flow exceeded ~3/4 throttle. The tickler isn't a precision bleed so the magnitude of the effect will vary between carburetor bodies.

Whether or not it helps speed up the process remains to be seen, but while waiting for the adjustable float to arrive I made a jig I sawed from a few pieces of scrap Al that gives me access to the float while the bowl is full. My hope is this will let me tweak the actuating arm for the needle in "real time" rather than having to remove the bowl from the carburetor body each time I need to make an adjustment. The Amal site says these floats have "stainless steel tangs which can be bent to alter the fuel level," but whether or not I can accurately do this in situ remains to be determined.

The first photograph shows that the jig holds the bowl flush against the bottom surface, with cutouts to hold the pivot pin in place and give access to the area around the needle. The second photograph shows that after I welded a "stand" to it I then faced the bottom of the stand to make its surface accurately parallel with that of the surface that supports the bowl. Measured on a surface plate the two surfaces are parallel to within the 0.1-deg. resolution of the digital protractor. The final photograph shows the jig mounted on an adjustable table set at 14.5-deg. I bolted it into the slot on the left so the scale on the table also can be seen but in use it would be in the slot on the right to give room for the tubing from the bottom. This also relies on the mounting surface of the adjustable table being level (in this case, the mill's table), which it is.


Attached picture FloatLevel10.jpg
Attached picture FloatLevel11.jpg
Attached picture FloatLevel12.jpg
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 04/24/19 9:31 am

Originally Posted by gavin eisler
You could add weight to the float, that will raise the fuel level.
Just exactly how , I dunno, never done it, whatever glue is fuel resistant and a short bit of cable tie maybe?


Or you could take weight off the needle.
Or change the seat height as we have been doing with concentrics for ages to get them properly balanced on A65L's
Apparently their is both a breass & alloy needle available and it makes quite a difference to the fuel height depending upon which one you use
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/24/19 9:38 pm

Originally Posted by John Healy
[quote] While the action of the Stay-Up float barely lifts the needle as design, bending the tangs to set the float level makes things worse.
I'm hoping John's comment refers to ham-fisted attacks on the tangs with Vise-Grips, not delicate changes made with surgical precision.

Unfortunately, tracking now shows my 'stay-up' float won't be delivered until tomorrow. To further be ready for its arrival, the first photograph shows I marked the float bowl at the 4.3 mm and 6.1 mm upper and lower limits for the level in the center of the bowl.

Because of the 15° tilt the float will have to rise higher than if it weren't tilted, the second photograph shows how far into the main body the float can move before it tops out. It can go into the body by 0.080", plus another 0.034" for the thickness of the gasket, for a total of 0.114". If it projects further above the float bowl than this when I set the level I'll have to devise a solution.


Attached picture Concentric15.jpg
Attached picture Concentric16.jpg
Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 04/24/19 11:26 pm

MM: We can supply you with one that is .050".
The Stay-Up float can be machined.
If you have seen as many bodies that have been bent from over tightening as I have you would be a believer.
When you get the float notice the clearance it has on the pivot!

Quote
Unless the engine shakes which, of course, none of them do.


You might think about a dynamic fuel level with the float vibrating up-and-down on the loose pivot pin.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/25/19 12:38 am

Originally Posted by John Healy
f you have seen as many bodies that have been bent from over tightening as I have you would be a believer.
I'm sure I haven't seen 1% the carburetors you have but I've seen enough that I'm already a believer. The bowl I used for the photograph in a recent post looks suspiciously like it had been held against a belt sander, as does the mounting flange on the Concentric that came on my BB Gold Star.

Originally Posted by John Healy
MM: We can supply you with one that is .050".
A thicker gasket can be part of Plan B (or C, or...) once the float arrives and I see what will need to be done. However, Plan A is for the new float to result in a perfect fuel level without any effort on my part...

Originally Posted by John Healy
You might think about a dynamic fuel level with the float vibrating up-and-down on the loose pivot pin.
No, I don't want to think about that. First, Gold Stars don't vibrate, and second, what I don't know can't hurt me...

Getting serious for a second, the float has to take up all the slack in the pivot before it can press the needle against the seat. It seems to me that once that happens, any vibration (worst case, such as from a Triumph engine...) only can open the needle to the extent the vibrations are able to push the float down into the fuel. This would be the same issue irrespective of the tightness or looseness of the pivot.

On a different (but not completely unrelated) topic, my data logger has two analog outputs, one that comes pre-programmed to put out 1-2 V for mixtures in the range 10:1 - 20:1. For no good reason, other than I like instrumentation, I found a 0-2 V meter whose shape is ideal for taping to the top of the LM-1. I checked its calibration and it is pretty good over the range 1.0-1.5 V where it would be useful. I already know that the AFM shoots up past 20 when I close the throttle so it doesn't matter that 2.0 V (20:1) applied to this meter causes it to display 1.9V (19:1).

Yes, I know the meter is only using half its range (or, 1/4, since I only care about the range 10:1 - 15:1), but the meter is the right shape and was available, and I actually only care about the saved data anyway, not a "real time" display. But, what's the fun in not exploring possibilities when you have the opportunity to?

Note: The LM-1 somehow lost its 'Calibrate' button. Since the Gold Star doesn't vibrate it must have happened because I parked it next to a Triumph.


Attached picture Innovate03.jpg
Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 04/25/19 2:35 pm

MM Just a thought. Why do they go to some lengths to rubber mount a remote float bowl on a non-vibrating Gold Star's remote float bowl? Is it because they can, an engineers job was at stake if he didn't come up with something to justify his existence or does vibration effect the action of the flow of fuel? Does the spring/plunger in a Mikuni's needle act to dampen (change resonant frequency) effects of vibration? Who better to ask such a question?

I haven't followed this thread. I missed the part where you explained what problem you found when riding the bike. Beside your drive for understanding, why do you keep working with the slanted spray tube. You are going to have a lot of information to benefit someone tuning a two stroke, when I believe you are going to end up with a straight cut tube in the end.

Back in 1959 when I worked at Andrew's Motorcycle Shop in Boston we would have a standing bet when Pete sold a Gold star. It was how long before we got a call that the front fender braces would brake and/or the fender fell off.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/25/19 5:15 pm

Originally Posted by John Healy
I missed the part where you explained what problem you found when riding the bike. Beside your drive for understanding, why do you keep working with the slanted spray tube. You are going to have a lot of information to benefit someone tuning a two stroke, when I believe you are going to end up with a straight cut tube in the end.
Some irrelevant background is that this is the bike whose magneto Ken Bell "restored" twenty-some years ago, sending me off on my quest to understand everything there is to know about magnetos when it failed after only a few miles.

Anyway, before I knew anything about magnetos, I also didn't know anything about carburetors (as opposed to now, when I know enough to inflict headaches on myself). But, but for some reason I no longer remember, before I had finished rebuilding the bike way back then I swapped its GP for a NOS 1036. Since I knew nothing about carburetors (or magnetos, or Gold Stars for that matter) the local Gold Star expert got it running for me (nb. the same guy from whose widow I later bought my BB and Catalina).

I haven't used this bike for a very long time, but in the recent process of reconfiguring it into more rideable non-clip-on configuration I looked inside the carburetor. I found it was in fully 2-stroke configuration and that is what prompted the title to this thread. I then swapped the jet block, needle jet, and needle for 4-stroke versions, and pressed a 4-stroke spray tube out of a sacrificial body. But then the flow bench reared its ugly head. Plus, I discovered the restriction shown in the photograph, that I also found in 2-stroke 600 and 900-series bodies in my collection, but in no 4-stroke body. I can't remember having seen this restriction mentioned in any book, magazine, or on-line post, although it turns out have an effect ~40% as large as the spray tube. So, along with the spray tube do I drill the "undocumented" restriction out? Unlike swapping spray tubes doing so would be pretty much an irreversible decision.

Diversions, including making flow bench measurements, upgrading my DocZ rollers, and finding that not pre-lubing the timing case after such a long time caused the breather to seize in the case, brings us up to today. At this point I've only made two (or three?) jetting runs, as a result of which I'm waiting for a stay-up float to be delivered later today so I can properly adjust the fuel level before proceeding.

Again, just swapping the spray tube would not complete the transformation to 4-stroke configuration. There's still that undocumented restriction in the compensating air passage whose effect on the depression is not negligible (e.g. 0.250 psi at 3/4 throttle with a 2-stroke spray tube but without that restriction, 0.225 psi with it, and 0.188 psi for a 4-stroke body).

I probably wrote somewhere in this lengthy thread that my plan is to try to sort out the jetting with the 2-stroke spray tube and restriction in place. Should I fail, I'll make the final two modifications. But, whether or not I succeed with the current semi-2-stroke configuration, the results I find will be a service for all of humanity since future Gold Star owners will know exactly what modifications they need to make if they are to install a 1036 or 1038.

Originally Posted by John Healy
we would have a standing bet when Pete sold a Gold star....
Ah, now I understand the source of your misunderstanding. Your experience was with East Cost Gold Stars. Mine are West Coast models...


Attached picture Concentric14.jpg
Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 04/25/19 7:15 pm

Is that grey hair I see in a recent picture? Carburetors can do that!

Its too bad that Tom Ullman isn't still around. He was the chief engineer for Grosvenor Works. He came to Grosvenor Works when they bought Zenith. One of the last things he organized was 10 sets of copies of carburetors for the Honda 6 reproductions. While getting information out of Barry Johnston was like "pulling teeth" (many bottles of expensive red wine), Tom would share information readily.

When we were having problems with MKII's on a Triumph 500 racer off the top of his head he pointed us in the right direction. His suggestions transformed our tuning problems. tuning. Grosvenor had several wet flow benches to work with. His measurements were that much closer to real time performance. He was able to set up the Honda carbs in the shop for the six so they worked right out of the box.

If any one knows where Tom retired to I would like some information so I can contact him.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/25/19 8:10 pm

Originally Posted by John Healy
Is that grey hair I see in a recent picture? Carburetors can do that!
A few days after a talk I gave at Boston College about ten years ago my host emailed an article from the student newspaper that mentioned my "salt and pepper hair." Since I knew I had brown hair I was offended, but my wife said "I hate to break the news to you, but..." It's still (barely) salt and pepper, but the mix isn't 50/50.

Originally Posted by John Healy
they worked right out of the box.
Nearly 20 years ago when I was getting my C15S ready to ship to Ireland I decided to put a Mikuni on it. The supplier assured me it would come properly jetted for my bike. The jetting I ended up with was nothing like it was out of the box.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/25/19 9:11 pm

Originally Posted by Magnetoman
"Air does bleed in through the tickler, but in the carburetor I tested that leak/bleed wasn't fast enough to keep up with the pressure drop once the air flow exceeded ~3/4 throttle. The tickler isn't a precision bleed so the magnitude of the effect will vary between carburetor bodies."

Can you desribe a route by which a throat depression will cause a bowl depression?

Is it more likely that this finding was an artefact of the the experimental technique?

As in primarily that the bowl had no fuel in it, the main jet orifice should have been blocked, as you had done with the pilot jet in one of your trials. Both should be blocked, or at least severely restricted, if air is the only medium in the system.
In the normal functioning of the carburettor, there is no air draw from the bowl, only fuel.
Wthout fuel in the bowl or deliberately blocked jets, the depression in the throat is free to draw massive amounts of air from the bowl, which bears no relation to how it functions with fuel in the bowl.

I wonder if John's mention of Wet flow benches may relate to this.

In operation, the only draw from the bowl is fuel.

Just suppose at 100mph at 6000rpm full throttle, 25 miles per gallon for illustration purposes.

This equates to about 5ml/s of fuel being drawn from the bowl. Thus, if the fuel supply to the bowl was closed, (wait for the engine to stop in short seconds, hopefully without damage) the air bleed via the tickler needs to allow 5ml/s of air into the bowl.

But of course, unless there is something amiss with the fuel supply to the bowl, the supply equals the demand, through the float valve within a small +/-.

So there is really very little for the tickler breather to do, and it is very easy for the loose fit of the components of the mechanism to equilibrate the pressure of the bowl atmosphere with external atmosphere.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/25/19 10:04 pm

Originally Posted by Magnetoman
"I don't think I discussed my use of 7" H20 for the flow bench test pressure, which I settled on after a series of preliminary set of measurements. As to whether this provides a reasonable set of flow conditions, ignoring overlap, if the cylinder of a Gold Star completely and uniformly fills during the downstroke that's 500 cc / one-half revolution of the engine. Converting this to cfm vs. engine rpm:

rpm______throttle position __
600 (idle)___~closed ________________5.3
1500 _______1/4 _________________ 13
3000 _______ 1/2 _________________ 26
4500 _______ 3/4 _________________ 39
6000 _______ full __________________53

Obviously, flow would be lower than these average figures when the intake valve was starting to open and when it was closing, and higher than average when the valve was fully open, but they give reasonable figures to check against. Note from the graph in an earlier post that a test pressure of 7" H20 resulted in ~85 cfm flow at full throttle, which is ~60% higher than the average flow calculated under operating conditions, so the flow bench settings I used put the carburetors in the right ballpark."


I do hope that I am wrong, but my calculation shows your calculation to be out by a factor of 4X.
As it is such a basic premise of the flow bench tests to be applicable to reality, I thought it best to mention it. As I say, I hope I am wrong, and will have no problem with that if so. I am merely playing devil's advocate for a double check.

IF there is an error, it enters at "CFM (500 cc x rpm x 2)" where I would use (500 cc x rpm / 2).

My reasoning is:

6000 rpm is 100 rev/sec. So each rev takes 0.01 sec.
The induction stroke is half a rev, it therefore takes 0.005 sec.
So in this rough model, 500cc is drawn through the carb in 0.005 sec.
= 100,000 cc/sec = 100 litres/sec (1 cubic ft = 28.32 litre)
CFM = 100/28.32 X 60 = 211.9 cubic foot per minute.

I sincerely hope that you can pick out the flaw in my calculation.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/25/19 10:32 pm

Originally Posted by koan58
I sincerely hope that you can pick out the flaw in my calculation.
Sorry, you're on your own.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/25/19 10:44 pm

I'm not sure what you mean by that statement, is it that my arithmetic is unique to me?
It is checkable by anyone else, so I don't think so.
Have you checked it yourself, or just dismissed it out of hand?
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 04/26/19 8:57 am

"if the cylinder of a Gold Star completely and uniformly fills during the downstroke that's 500 cc / one-half revolution of the engine. Converting this to cfm vs. engine rpm:"

Its a 4 stroke , the cylinder fills every 2nd revolution. 500 cc/ 2 revs. or am i missing something.?
maybe thats irrelevant for a flow bench.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/26/19 5:35 pm

Originally Posted by gavin eisler
maybe thats irrelevant for a flow bench.
It is. I gave that estimate to show roughly what the carburetor experiences in operation. Although the 7" H2O pressure I used happens to give similar flows as this estimate, the Reynolds numbers (flow velocity) would have to be considerably different to have an effect on the conclusions.

The stay-up float arrived in the mail yesterday but another mini-heat wave will have it 98 oF today so after I set the fuel level I'll start work on the jetting tomorrow when it will be a little cooler. However, and I can't emphasize this enough, I will have it completely jetted by the end of day on Sunday...

Since I have the 1036 off the bike, now would be a good time to flow test it, to compare with what I get with the 1038 and GP. I have an inlet trumpet for the Concentrics that is a pretty good approximation of the one on the GP so it should be a fair comparison. Also, I'll measure the 1036 with and without the K&N filter to see how much of a difference that makes. The results should be interesting.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 04/26/19 9:33 pm

Originally Posted by Magnetoman
"Although the 7" H2O pressure I used happens to give similar flows as this estimate"

My point is that your original calculated estimate is very wide of the mark, by a factor of 4.

Your estimate at 6000rpm is 53cfm, whereas correctly calculated it is 212cfm.

Irrespective of Reynolds numbers, I think that this huge difference in flow will cast considerable doubt on your findings so far at the low, erroneously estimated flow.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/27/19 1:24 am

Thanks to the jig I had made, which turned out to be quite useful, it didn't take long to get the fuel level adjusted. When I finished the first time the top of float was a little too high so would have hit the bottom of the main body. So, I took a bit off the top with the belt sander. The loss of mass wasn't enough to make a measurable difference on the float level. I don't have a 'before' picture of the float but if you find an image on the web you will see the tangs come straight out from the float. The first photograph shows how much I had to bend the tangs to get the float level where I wanted it.

The second photograph shows the bowl in the jig with the fuel at or near the final level (I don't remember if I made any further adjustments after taking this photo but, if I did, they were minor).

I drained and refilled the bowl a few times to make sure the level was repeatable, installed it in the carburetor, set it at 14.5-deg., and confirmed the level was the same as when the bowl was in the jig. This is shown in the third photograph. I also drained and refilled the complete carburetor a few times to check again on the repeatability.

I then turned to the flow bench. The final two photographs show most of the configurations of the 1036, 1038, and GP. Not shown is I also measured both of the Concentrics with nothing screwed onto their inlets. I did these measurements at 3" H20 and what I found for their flows in CFM was:

1036
'bare' 75.0
trumpet 74.8
cylinder 73.7
K&N 69.4

1038
'bare' 77.9
trumpet 78.5

GP
trumpet 85.1

As would be expected, air flow takes a hit when an air filter is added. In this case a K&N RC-1250. I'll come back to the effect on performance in a moment.

As also would be expected, the smaller 1036 flows less air (~5%) than the larger 1038. But even though the 1½" GP is identical in size to the 1038 (to within 0.004") it flows 8.5% more than the Concentric. So, if flat-out racing is the goal, it has to be a GP.

As I mentioned in an earlier post, the SuperFlow manual says the h.p. of a well-tuned racing engine can be calculated from the measured flow into the head using the formula:

h.p. = 0.35 x CFM x (15 / test pressure in inches H20)0.5

I made the above measurements at 3" H20 so what this formula says is using a GP will restrict the maximum h.p. attainable from a Gold Star to:

h.p. = 0.35 x 85.1 x (15/3)0.5 = 66.6 h.p.

Since not too many Gold Stars are capable of producing that many h.p. it means the limitation comes from the cams and head, not the carburetor. [*]

Returning to the 1036, according to this formula a filter would limit the maximum achievable h.p. to 54.3. Since my 'Competition' was tested to have 41.7 h.p. when it left the factory, this K&N filter isn't much of a limitation.[*]


[*]Air flow through several restrictions in series (e.g. an air cleaner followed by a carburetor followed by a head) is a bit more complicated than I've let on here, but for my purposes it's good enough to know that using a 1036 instead of a 1038 or a GP isn't in any way going to limit my opportunities for speeding tickets. No matter what the speed limit is.


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Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 04/27/19 9:22 am

While you are testing bell mouths any chance of fitting the short style to the concentric?, I always thought they were better than the long types, would love to see the numbers.

also , any chance of part throttle comparisons, IME , long bell mouths do something to the middrange that changes NJ sizes for optimum running.
Posted By: gunner

Re: Correct needle for 1000-series Concentrics? - 04/27/19 9:45 am

Any chance you could also test the Amal screw on cone air filters that are now available?

These filters dont seem to be as long as the K&N type that you have but at least they screw on and you dont need to rely on a jubliee clip.

I've been thinking about buying one of these for for a while so any details on how they actually perform would be great.

I'm impressed by your float level tests, my only comment is what effect actual riding has on the level. For example if you are climbing a steep hill or riding over rough ground would the float level change? I guess you couldnt do much in these circumstances anyway so getting it spot on in the workshop is good.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/27/19 1:53 pm

Originally Posted by gavin eisler
While you are testing bell mouths any chance of fitting the short style to the concentric?,
I was primarily interested in seeing the differences between the 36 mm, 38 mm, and GP at full throttle, as well as the effect of the air cleaner, so I didn't do a thorough test at all throttle settings. Also, the long trumpet I used was the only one in the box that fit the 1000-series bodies so that's all I could measure.

Looking at the figures for the bare carburetors, if flow depended on area the 38 "should" have flowed 11.4% more than the 36, but if it depended on circumference (because of "drag" due to the walls) it "should" have been 5.6%. It actually flowed 3.9% more, showing that "aerodynamics" is more complicated than just simple geometry. However, the fact the flow is much closer to the circumferential value seems to indicate that edge effects are important. It's probably no coincidence that Amal went to a fair bit of trouble to smoothly blend the trumpets of their GPs and TTs into the carburetor bodies.

Coming back to an earlier point in this thread, with the 36 the air has to make a small step down when entering a DBD head, while with the 38 it has to make a small step up. Given the previous paragraph, it's likely that in both cases the step has some significant effect on air flow. If I had a spare Gold Star head on the shelf I would love to explore the effect of this step on the total throughput with these same three carburetors.

Originally Posted by gavin eisler
also , any chance of part throttle comparisons, IME , long bell mouths do something to the middrange that changes NJ sizes for optimum running.
Aside from not having a selection to choose from, before taking the time to make measurements across the range of flows I'd like to inspect how well different ones fit on the carburetor bodies. As I mentioned, the ones on the GP and TT seem to fit better than would be the case for universal screw-on trumpets.

Originally Posted by gunner
Any chance you could also test the Amal screw on cone air filters that are now available?
I could if I had one, but I don't. I have a surprising amount of "stuff" to choose from, but I definitely don't have everything nor in all sizes.

Originally Posted by gunner
example if you are climbing a steep hill or riding over rough ground would the float level change?
That's a very interesting question. Hills are easier to answer. Google tells me that most of the steepest/highest mountain passes in Colorado have gradients of ~7%, but the worst is 9.4% at 11,361 feet. Just where your engine is producing the lowest power it faces the steepest slope. And, since my Gold Star now has its float set for 15-deg., going up that slope will have it at 5.6-deg. This will close the inlet valve sooner, which will lower the fuel level and make it leaner. But, leaner is better at altitude so maybe that's not so bad. Also, it's not very common to find long climbs that aren't interrupted by short downhill sections so the level will find itself going up and down even as the average altitude keeps increasing.

As for rough ground, we know that somehow the carburetors continue working despite that. The second photograph in my previous post shows there isn't a lot of room for the fuel to slosh around in a Concentric. If it sloshes forward to raise the level at the front of the carburetor, it lowers it at the back, so the fuel level in the center -- where it matters -- stays the same. The same is the case for side-to-side sloshing. Thanks to gravity, after the apex of a jump on an American-style TT track the bike falls but so does the fuel with the same acceleration so the level stays constant on the way down. When the bike hits the ground again it seems like all hell might break loose with the fuel, but the roof of the float chamber limits how high the fuel can go to a value not all that much higher than the proper level so any such temporary surge can't take it too far from where it should be (again, look at the photograph in my previous post).

I'm not saying my explanations in the previous two paragraphs are correct. But, knowing that the carburetors actually do work under those circumstances helps come up with plausible reasons for why. If carburetors didn't work there could be equally plausible-sounding reasons for that as well...
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/27/19 6:43 pm

Now the flow-related experiments just need to be extended to 36 and 38 (long and short bodied) Mikunis, as well as say, Dellorto (SSI and PHF) and perhaps Keihin! Then there's the difference between a bored 34mm Mikuni (to 35.3) and a 36mm allegedly, the bored 34 flows more. Extending that thought, boring the 36mm Concentric to 38 might pick up the flow, and get closer to the GP than the 38?

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/27/19 7:42 pm

Originally Posted by Kerry W
Now the flow-related experiments just need to be extended to 36 and 38 (long and short bodied) Mikunis, ...
boring the 36mm Concentric to 38 might pick up the flow, and get closer to the GP than the 38?
I have a 38 mm Mikuni as well as a spigot-to-flange adapter for it. Unfortunately, it came to me without a slide so I can't make a valid flow measurement.

As for a Concentric ever challenging the supremacy of the GP, the photograph shows why that's unlikely. The "ordinary" Amal on the left (a Monobloc) has a flow-disrupting change in shape between the trumpet and the carburetor while the "performance" Amal on the right (a TT) provides the air with smooth sailing all the way.


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Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/28/19 2:51 am

Agree: a 'cooking' Amal is unlikely to come close to the TT or GP for flow.

In recent times, I had a DBD road-racer that came to me with a 38 Concentric fitted and the 1 1/2" GP in a box. The PO had found that, while the GP made for a (slightly) faster bike, lap times were better with the Concentric and it was substantially nicer to ride. It ain't all about power!

In a similar vein, the BSA/Triumph triple racers were initially run with 3 x GP's (cant recall the size), but quickly went to Concentrics.

What's the shape under the Concentric slide like? (i.e. is it a bit of a void?)...cant recall offhand. Might there be scope for notable improvements in flow with a 'UFO'? Proof that these things work is in the need to halve the pilot jet size when used in a Mikuni..
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/28/19 2:53 am

Life intruded on motorcycle work today so I didn't have time to do much more than install the 1036 on the Gold Star. Once installed, following the 'Carpenter's Rule' of "measure twice, jet once" I checked the fuel level and found it was exactly where it should have been had I made all the angle measurements and float level adjustments correctly. Which, apparently, I did. As can be seen, the level is just a tiny bit above the lower limit of the 4.3-6.1 mm range at the center of the bowl. Mission Accomplished.

The last step when assembling the carburetor was to coat both surfaces with Permatex, let the solvent evaporate for ~20 minutes, put the gasket in place, and then attach the bowl using John Healy's recommended 75 ft.lbs of torque on the screws (actually, I couldn't find John's recommendation but I'm pretty sure I remember that figure correctly...). Rather than Permatex I coated both sides of the phenolic spacer on the head with EZ Turn petcock grease to eliminate the possibility of air leaks at that joint. Once I'm happy with the final jetting I'll Loctite the mounting nuts. However, it would be premature to do that now since I don't know yet whether I'll have to switch the spray tube and/or drill the compensation air passage before the fat lady sings.

Special tools I made for this were a float bowl plug with Tygon tube for determining the fuel level, drift for removing and installing spray tubes, jig for holding the float bowl on a machinist's table with adjustable angle, and drift for moving the seat in both directions. I found that using this drift in my mill (with its DRO) lets me press the seat with nearly 0.001" precision. Of course, the next time I need to work on a Concentric I won't remember I have half of these tools so will end up making them again...


Attached picture Concentric22.jpg
Posted By: gunner

Re: Correct needle for 1000-series Concentrics? - 04/28/19 4:38 am

Quote
75 ft.lbs of torque on the screws


Sounds excessive for a carb screw, maybe you meant 7.5ft.lbs?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/28/19 5:48 am

Originally Posted by gunner
Sounds excessive for a carb screw, maybe you meant 7.5ft.lbs?
I was being facetious. I applied the right amount of torque[*] with a screwdriver; not too much, not too little.

[*]i.e., what felt right, not necessarily what was right...
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 04/28/19 8:53 am

I'd have suggested an impact driver..
Posted By: Jerry Roy

Re: Correct needle for 1000-series Concentrics? - 04/28/19 2:36 pm

Originally Posted by Magnetoman
Once I'm happy with the final jetting I'll Loctite the mounting nuts. However, it would be premature to do that now since I don't know yet whether I'll have to switch the spray tube and/or drill the compensation air passage before the fat lady sings.



It would be nice if someone with some spare time on their hands would find out if these, https://www.youtube.com/watch?v=-cfim-AqZws, came in 26 TPI SAE size. wink
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/29/19 4:11 am

The correct float level cured the lack of response of the pilot jet, so I set the pilot mixture to ~14:1 and made a jetting run. At ~1/8 throttle, where the slide is also contributing, it dropped to ~11:1 indicating the #3 slide is too rich. So, I decided to turn it into a #3.5, which requires increasing the cutaway by 1/32"=0.031" to make it 7/32"=0.219". I marked that amount on the slide and checked with 0.100"+0.119" gauge blocks as shown in the first photograph.

Rather than attack the side with a file I machined a length of Al rod to be a tight slip fit over the slide and slit one side of it, as shown in the second photograph. The third photograph shows the cutaway was machined when the slide was held at 15-deg. so, as the fourth photograph shows, that's what I did as well. However, I decided to stop after removing 0.020" to make it a #3.33 since I always can take more off later if required.

The carburetor is back on the bike ready for the next jetting run.


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Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/29/19 10:50 pm

If it's not one thing, it's another. Once I was back on my local street at the end of yesterday's jetting run I hit the button to stopped recording data. A half mile later it started running rough but I had enough power to make it up my steep driveway by revving the engine and slipping the clutch. I didn't think any more of it. Until today, when it started with difficulty (thank you!, thank you!, DocZ rollers) and missed badly unless I managed to coax it to higher rpm, at which point it revved freely. When the rpms dropped, the missing began again until it would die.

It acted as if it has a plugged pilot circuit so I removed the carburetor, disassembled it, inspected the jet (not plugged), and blew compressed air in both directions through the pilot circuit. Unfortunately, that made no difference so, since I'll be tied up the rest of today, tomorrow it has to come off again. Something must be plugging the tiny holes at the back edge of the slide.
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/30/19 1:02 am

Just a thought: do you have an auxiliary fuel filter between the tank and the carb ? If dirt is causing you problems, would it be worth installing a good filter?

. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/30/19 2:16 am

Originally Posted by gREgg-K
do you have an auxiliary fuel filter
Well, you see, it's like this. I don't have just one filter, I have three different ones to choose from. All are sitting on the workbench where I had them at the ready, to be installed after I got the jetting sorted out. Sigh...
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/30/19 1:39 pm

Originally Posted by Magnetoman
Originally Posted by gREgg-K
do you have an auxiliary fuel filter
Well, you see, it's like this. I don't have just one filter, I have three different ones to choose from. All are sitting on the workbench where I had them at the ready, to be installed after I got the jetting sorted out. Sigh...

Ah, those fuel impurities are so cunning! They refused to be fooled into flowing through your workbench on their way to the carb ... ;-)
.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/30/19 8:00 pm

Originally Posted by gREgg-K
Ah, those fuel impurities are so cunning!
I'm presently stumped. First, I don't understand why new fuel filters still sealed in their packages on the workbench were so defective that they failed to stop impurities getting into the pilot circuit. And second, why there was no sign of those impurities when I inspected the carburetor this morning.

Rather than try to clean the pilot circuit on the bike I removed the carburetor so I could see and understand the problem. With the air screw removed I used a fiber optic bundle to send a million foot-candles (estimated) of light into the little chamber under the two pilot inlets while under a stereomicroscope to see if I one or both of them was blocked. Neither was blocked, nor could I see any sign of machining swarf through the air screw hole (although I'd have to remove the Welch plug to be 100% sure of that). Even though I could see neither hole was obstructed I still dropped the non-sharp ends of #65 and #71 drill bits through the two holes. I didn't remove the bowl this time because yesterday I had done so and the pilot jet wasn't blocked.

Before putting the carburetor back on the bike I inspected the needle to be 100.0% sure I hadn't installed the wrong one at some point in the last day or two, but it is the correct 2-ring 4-stroke needle. The DocZ could get it intermittently started but it ran very rough and quickly died. I did succeed in coaxing the rpm up once and as long as I kept it above ~3k rpm it ran great, but when the rpm dropped below that it started missing badly and quickly died. The only thing I had done to the carburetor between the bike running rich but OK-ish and it running horribly was to cut the slide so it's now a #3.33, but that doesn't explain the symptoms.

OK, stepping back for a moment, 90% of carburetor problems are electrical. I realized that the rpm pickup clamp is clamped around the HT lead at the magneto so I removed the clamp, thinking perhaps the spark was shorting through it. No luck. The bike behaved the same, barely starting but running well if I could get it over 3k rpm. Although I rebuilt the magneto myself, all possibilities are open for consideration at this point. I've gone through most of a box of spark plugs over the past week so the issue isn't that I'm using an old plug. The easiest checks will be to see if the pickup brush is OK, the HT lead has the correct ~0 Ohms from end to end, or the timing has slipped (although retarded timing wouldn't explain the missing at low rpm).


Attached picture FuelFilters.jpg
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 04/30/19 9:31 pm

A number of years ago I had a Concentric which would not respond to the pilot screw, and the jet etc was clear. I'd cleaned and blown out the passages so many times that I was sure it could not be blockage in the body.

Turned out to be a blockage in the body ... there are three a longitudinal drilling from the air inlet (back) end of the carb body, beneath the main venturi. One of them is blocked with an alloy plug after machining the passage behind it. I drilled and tapped the exposed end of the plug for a 4-40 (UNC) screw, and then made a small "jacking" extractor to pull the plug out. Sure enough: poking a stiff wire through the now-exposed passage liberated years of old [email protected] that had been blocking it.

Machined up a new plug, pressed it in, and all was well again.

Hope this is of help, or at least some inspiration!
.. Gregg
Posted By: gunner

Re: Correct needle for 1000-series Concentrics? - 04/30/19 9:48 pm

With this type of scenario a back to basics approach usually helps, in other words check the following as starting point (all of which you already know I'm sure):-
- ignition timing as already mentioned perhaps also points, condensor & HT cap?
- sufficient fresh fuel in the tank and taps operating correctly with adequate flow
- drain float bowl, check for water, debris etc. blow out carb with compressed air, check for air leaks at manifold

If still no joy, substitute carb, magneto etc. until issue resolved.

Usually it;s a tiny fault which causes a huge problems with smooth running and progression through the revs.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 04/30/19 11:05 pm

Originally Posted by gREgg-K
the now-exposed passage liberated years of old [email protected] that had been blocking it.
Originally Posted by gunner
With this type of scenario a back to basics approach usually helps,
The 1036 is essentially new but, all possibilities are on the table. I can't do anything more with the bike today but my current thinking is to assemble the 1038 with the same jetting as the 1036 (i.e. not swapping components from the 1036 but using different ones of the same sizes) so that the only thing that will remain unchanged is the slide and needle. The 1038 won't have a perfect float level, but I'll see if the low rpm behavior is changed. If the issue is electrical a different carburetor can't make it better, only the same or worse. What I find will inform my next steps.

The way it's behaving now there's no way I even could get it started it without the DocZ. A non-starting, non-running bike certainly would make the troubleshooting process a lot more difficult.

Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 05/01/19 12:17 am

I suspect that you've set a higher fuel level than would ever have been readily practicable.
That probably wouldn't matter much in most applications, but in your 15 deg downdraft it does make a difference.
Because of the angle, the fuel level is much closer to the pilot jet at the front end of the carb, making it much easier for fuel to be drawn through the pilot system.
I anticipate that you will say that it's the level at the spray tube that's important, but no, the pilot jet is a separate system, with its own head.
This could easily cause excessive low throttle richness.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 05/01/19 8:32 am

What if the AF meter readings are wrong?
At 11 to 1 it ran fine, corrected to 14:1 it doesnt run fine.
I recall Kevin Roberts found this to be the case when setting up his Triumph, needed more fuel than the meter suggested was optimal.

A couple of simple checks, fill float bowl, switch off fuel. If the level is wrong it will come good as the bowl drains.

If it starts, apply a palm across the bell mouth to temp enrichen mix, it may be the slide was fine at 3.
Of course it will be something else. But these are easy quick tests.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/01/19 3:17 pm

Originally Posted by gavin eisler
What if the AF meter readings are wrong?
At 11 to 1 it ran fine, corrected to 14:1 it doesnt run fine.
That's a reasonable question. However, I'm paying as much, or more, attention to standard tuning clues as I am to the meter.

I used the meter to adjust the pilot air screw to 14:1 at idle when I was halfway through the run I made that caused me to increase the slide from a #3 to a #3.33 and I can't say doing so made much of a difference. It still behaved too rich at low throttle settings (which is why I cut the slide). The issue developed at the end of the subsequent run (the first with the #3.33) going from OK-ish to not OK at low rpm. I had to remove the pilot air screw to shine light in it to inspect the two tiny outlet holes and it was at ~3/4 turns out when I removed it but I put it back at 1-1/2. The low rpm behavior was identical.

It acts as if either something shifted inside the hidden part of the pilot passage to block it, or something is wrong with the sparking at low rpm. I hope today's test with the reconstituted 1038 points toward the solution.
Posted By: kevin roberts

Re: Correct needle for 1000-series Concentrics? - 05/01/19 3:51 pm

Originally Posted by Magnetoman
Originally Posted by gavin eisler
What if the AF meter readings are wrong?
At 11 to 1 it ran fine, corrected to 14:1 it doesnt run fine.
That's a reasonable question. However, I'm paying as much, or more, attention to standard tuning clues as I am to the meter.


^^^yes. i found the best performance with my T120 at WOT to be around 11:1, using a stopwatch.

it's not that the sensor readings are wrong, it's that the uncorrected numbers they give will vary depending on cylinderhead design and state of tune, as well as combustion chemistry. an inefficient triumph hemi combustion chamber running as best it can might generate tailpipe numbers very different from a better-designed BSA or norton.

but you can use testing to find out what the best numbers are, and use the sensor to re-set to them whenever you change something
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 05/01/19 4:29 pm

Use a dyno. Find the best HP reading. Note the result using an exhaust sniffer. Note atmospheric conditions.

Baseline.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/01/19 10:40 pm

The bike behaved basically the same with the 1038 as it had with the 1036 so it's back up on the stand to start checking electrics. However, getting to this point took more effort than it might have.

I first carefully inspected the 1038 and found one of the pilot inlets partially blocked. I checked all the other passages and inlets, using a can of compressed air to make sure all were free. With that taken care of I assembled it to the same specs as the 1036 but using different components so that only the slide and needle would be common between the two.

After the 1036 was off the bike and the 1038 was on I found that no fuel would come out of the tickler. Making a long story short, I worked backwards to the point where I tried to flow fuel into the free standing bowl without even the needle or float present. Only when I lowered the bowl to pick up my iPhone did a dribble flow into it. And, yes, there is fuel in the tank, and it flows quite freely through the new filter I installed. However, since the filter was something different than before, I replaced it with a length of tubing. Still no flow into the bowl. Although I said in a previous post that "all possibilities are on the table," that doesn't include violating the laws of physics.

I then blew 120 psi shop air through the inlet connector to the float bowl, after which fuel flowed freely. When assembling the carburetor I had inspected the bowl to be sure nothing was blocking the seat, and the banjo bolt to be sure it was completely free, and used canned air to flow through the banjo itself, but clearly something had been inside the banjo that let low pressure air pass but blocked fuel.

Anyway, with this "interesting" problem taken care of, the tickler worked, but the bike only revved freely cleanly beyond 3k rpm, just like with the 1036.

The 1036 has two advantages. It's essentially new, and the transition to the head doesn't have a small step up. However, although used, the 1038 also has two advantages. It's a right-hand carburetor so tickling is easier than with the left-hand 1036 (as is access to the pilot and idle screws), and having the tickler on the right also makes it easier to put the carburetor on and take off the bike. The studs are long enough that the nut on the tickler side can't be removed (or installed) unless the carburetor is pulled ~1/4" away from the head. Even then the tickler is still somewhat in the way making installing or removing the inside nut and washers without dropping them a bit fiddly.


Attached picture 1038_01.jpg
Attached picture 1038_02.jpg
Attached picture 1038_03.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 05/02/19 5:07 am

If maintaining the 'set' float height is a primary concern, why not swap the bowls between the 36 and 38mm Concentrics?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/02/19 4:10 pm

Originally Posted by Kerry W
If maintaining the 'set' float height is a primary concern, why not swap the bowls between the 36 and 38mm Concentrics?
Swapping the entire carburetor follows the general principle of making one change at a time. By switching the entire carburetor (minus slide and needle), if the bike had run better (which it didn't) it would have pointed at there being something wrong with the 1036, which includes its float bowl. However, had I switched bowl and it not run better, I wouldn't have known whether the cause was the float bowl or the electrics.

Last night I tried to make an estimate of the timing by the stick down the spark plug hole method, but with the kick starter on one side and the points on the other, even with a mirror I couldn't get it close enough so after two tries I gave up on doing this quick and easy. I'll jack the rear wheel off the lift today so I can use it to advance the engine incrementally. As I wrote previously, I'll check the things I can check in situ (timing, points gap, spark plug wire and cap, and HT pickup). Should I not find anything, the magneto will come off so I can spin it on my three dynamic testers.
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 05/02/19 4:32 pm

Just had a thought, MM.

Why not put a degree wheel on the Goldie's crank, pull the spark plug, and drive the rear wheel on your DocZ rollers. That will allow you to strobe the ignition timing, and at least qualitatively evaluate the spark intensity.

.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/02/19 4:58 pm

Originally Posted by gREgg-K
Why not put a degree wheel on the Goldie's crank, ...
I added a removable cross-bar to the DocZ so I could leave a bike in place between tests (which I had to modify considerably to clear the 'speedway' roller), so that certainly would be possible. However, I'd have to remove the primary cover and devise a way to rigidly mount a timing disk to the crank. Neither is beyond the scope of doing, but at that point it would be nearly as easy to pull the magneto and test it directly.

However, your post has given me a great -- or horrible; which it is remains to be seen -- idea. Removing the tach drive only requires removing two screws (and safety wire), leaving two holes to use to mount my as-yet to be designed and fabricated degree wheel holder. If I used my Triumph timing disc I wouldn't even have to multiply by 2 (or divide by π, or whatever) since its angles incorporate the camshaft correction factor.

I already have bearings in various sizes I could use, as well as Oilite material, so I could have something ready in a few hours. It's your fault for seeding this idea since now I must have this tool. However, since having it isn't essential for addressing the present problem I'll do my best to put it out of my mind until after I get the bike running well.

Update: The engine is firing at 1.6 mm BTDC at full advance, which is a bit less than 3°. I've already had words with the incompetent rebuilder who it's now apparent didn't sufficiently tighten the pinion when he installed the magneto after rebuilding it. Believe me, he's every bit as upset with himself as I am with him. However, why this resulted in it running terribly below 3k rpm, but seemingly fine above that, I don't know. But, once again the truism that 90% of carburetor problems are electrical proves, well, true.

Posted By: gunner

Re: Correct needle for 1000-series Concentrics? - 05/02/19 7:46 pm

Hey go easy on the incompetent rebuilder, I;ve had one in my garage for years and although he's caused countless problems at least he doesnt charge much smile
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 05/03/19 5:35 am

Reminds me of a friend who bought a nivce little Velocetter MOV 250cc road racer. He bought it off an old mate, who was a well-known dealer in these things since before WWII...

First thing I noticed, looking at the bike after it arrived in my friend's shed, was that the cylinder head was different to the one I'd seen fitted to the bike at the last outing. And them we found it wouldn't run. The bike would fire once, but then steadfastly refuse to cooperate any more until the ignition timing was reset. How had it slipped? mag pinion was lapped onto the mag armature, etc, etc. No joy.

Then the numbers of teeth on the respective gears was counted...it seems the mag had also been changed, and for some reason, so had the mag pinion. Exact details escape me, but the 'new' mag pinion had a different number of (fibre) teeth to the one that had run successfully..though still meshed acceptably. Consequently, after setting the timing, the mag would fire on the first compression and then get progressively further 'out of time' with the crankshaft..

Thanks that make you go 'Hmmm'...

KW
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/03/19 5:14 pm

Originally Posted by Kerry W
Reminds me of ...
Which reminds me of the taillight that burned out in my car many years ago. I bought a replacement in the auto parts store, but soon discovered it had blown out as well. Taking no chances I removed the bulb from the socket and took it into the store and bought one exactly like it. It blew out. At that point I had the person look up the correct part number for the bulb I needed and it was different than the replacement I originally bought and then carefully duplicated.

It's easy to fall into these traps. In the case of my Gold Star, the story begins with it running OK-ish, I changed some internal carburetor components, and it then ran terribly. If nothing else this emphasizes the fact that correlation does not imply causation, which is well to remember when troubleshooting (although correlation does not mean there might not be causation).
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/04/19 1:05 am

With a lot of resolution the details of setting the timing gets complicated. I use the inductance of the primary to determine when the points open, since that changes from 0.00 (on the mH scale) to ~5 so there's no mistaking it. However, with a resolution of ~0.1-deg. on the crank angle the inductance doesn't just abruptly jump between those two limits, it sort of oozes between them. Further, if I stop advancing the engine just before the full value of inductance is reached (or anywhere up to that point) and wait, it slowly oozes lower over a period of many seconds. I think part of that oozing may be due to backlash of the gears relaxing, but some of it may be due to the points rubbing block relaxing under the pressure of being held partially open by the spring. If I had even ~5x lower resolution, so I could tell the difference between 38-deg. and 39-deg., but no better than that, I wouldn't see these effects.

If I'm right about the relaxation issues, both would be different in operation than they are when I set the timing statically. The engine would keep pressure on the gear train so there wouldn't be an opportunity for the backlash to relax, and the rubbing block would take on some steady-state amount of relaxation. The only way to know how much an effect this would have would be to accurately set the static timing, then check the timing with the engine running.

The other "detail" is the value of advance to use. Fifty years ago my Gold Star was tested by the factory at "39 degrees." I can set it to 39.0+/-0.1 degrees, but with today's fuels would it be better to use something other than 39 degrees? Unfortunately, I haven't found any definitive information on this. Yes, there are plenty of unsubstantiated allegations that more/less advance is needed because modern fuels burn slower/faster, but I've yet to find any actual data showing one or the other.

Anyway, today I set the timing at 39.0-deg (with pressure on the wheel to keep the backlash from relaxing). However, I didn't close up the timing cover so that tomorrow I can see if it has wandered off from that value.


Attached picture TimingDisc.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 05/04/19 12:39 pm

Originally Posted by Magnetoman
Originally Posted by Kerry W
Reminds me of ...
Which reminds me of the taillight that burned out in my car many years ago. I bought a replacement in the auto parts store, but soon discovered it had blown out as well. Taking no chances I removed the bulb from the socket and took it into the store and bought one exactly like it. It blew out. At that point I had the person look up the correct part number for the bulb I needed and it was different than the replacement I originally bought and then carefully duplicated.
If nothing else this emphasizes the fact that correlation does not imply causation, which is well to remember when troubleshooting (although correlation does not mean there might not be causation).


Just because you don't think you're paranoid doesn't mean they're not out to get you!
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 05/04/19 1:03 pm

Originally Posted by Magnetoman
<SNIP>. I think part of that oozing may be due to backlash of the gears relaxing, but some of it may be due to the points rubbing block relaxing under the pressure of being held partially open by the spring. If I had even ~5x lower resolution, so I could tell the difference between 38-deg. and 39-deg., but no better than that, I wouldn't see these effects.
If I'm right about the relaxation issues, both would be different in operation than they are when I set the timing statically. The engine would keep pressure on the gear train so there wouldn't be an opportunity for the backlash to relax, and the rubbing block would take on some steady-state amount of relaxation. The only way to know how much an effect this would have would be to accurately set the static timing, then check the timing with the engine running.<SNIP>
Anyway, today I set the timing at 39.0-deg (with pressure on the wheel to keep the backlash from relaxing). However, I didn't close up the timing cover so that tomorrow I can see if it has wandered off from that value.

I think you are correct about the various sources of lash contributing to what you are seeing. The workshop manuals always cautioned about rotating the engine in its running direction while checking timing, in order to take up lash in the gears. And as you say the dynamics of this are going to be quite different when the gear train is driven at speed with the cyclic loading of the cams.

.. Gregg
Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 05/04/19 2:16 pm

Magneto Man quote: "Update: The engine is firing at 1.6 mm BTDC at full advance, which is a bit less than 3°."

I'm not sure I'm following this statement. With a 89mm stroke and a 150mm long connecting rod, I get 1.6mm BTDC to be about 14 degrees instead of 3 degrees, if measured in crankshaft degrees. If measured in camshaft degrees, the ignition would be half of this number or 7 degrees. Can you clarify for me how you got 3 degrees BTDC?

Tom
[Linked Image]
[Linked Image]
Posted By: Jerry Roy

Re: Correct needle for 1000-series Concentrics? - 05/04/19 3:34 pm

Why did the BSA engineers put the lever up on the left handlebar with a cable going down to the cam plate in the magneto?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/04/19 4:45 pm

Originally Posted by koncretekid
Can you clarify for me how you got 3 degrees BTDC?
In fact, it is quite straightforward. All I needed to do was to convert 1.6 mm piston position into 0.063" and then use that figure when I looked up the crankshaft angle in a table I have where the piston position is in mm... In my defense, I'd like to think I would have caught this myself had the actual angle been needed for something other than confirmation that the timing had slipped.

In case someone wants to take numbers from your illustration, note that the actual stroke is 88 mm and the connecting rod length 164.3 mm (6-15/32").

Originally Posted by Jerry Roy
Why did the BSA engineers put the lever up on the left handlebar with a cable going down to the cam plate in the magneto?
I'm not sure what's behind your question. They had to put the lever somewhere, and their choice was either the left or the right handlebar.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/04/19 9:44 pm

Originally Posted by Jerry Roy
Why did the BSA engineers put the lever up on the left handlebar
The British drive on the left so having the lever there ensures that a motorist passing too closely in the other direction can't accidentally bump the lever and alter the timing. Or, perhaps, there's a different reason... However, if instead you had asked what the lever does, see the graph. At least, what it does to a KNC1 magneto.

As shown in the photograph I have the body marked in ~1/3 increments between full advance and full retard, with an indicating wire taped to the lever. The marks aren't perfectly spaced but I used a protractor to extract the positions for the plot (0.657 rather than 2/3 and 0.371 rather than 1/3). As can be seen, for my KNC1 magneto, at least, the amount of retardation is linear in movement of the lever with a full travel of ~41-degrees (engine)

The 2nd graph is a slightly more "universal" way of plotting the same data as in the 1st graph, but not based on the specific 39-deg. timing value I'm using on the 'Competition'. This makes it easier to see that moving the lever to a bit less than half its travel retards the ignition by ~20-deg., which is the amount built into most automatic timing devices. So, irrespective of what bike this magneto were on, a good place to set the lever for starting would be slightly less than halfway.

Attached picture MagnetoAdvance_KNC1.jpg
Attached picture MagnetoAdvanceLever.jpg
Attached picture MagnetoAdvance_KNC1_02.jpg
Posted By: Jerry Roy

Re: Correct needle for 1000-series Concentrics? - 05/05/19 1:13 am

Originally Posted by Magnetoman
Originally Posted by Jerry Roy
Why did the BSA engineers put the lever up on the left handlebar


As can be seen, for my KNC1 magneto, at least, the amount of retardation is linear in movement of the lever with a full travel of ~41-degrees (engine)


My point was that the cable / lever combination is anything but precisely accurate, and every time it is exercised, the odds of it being at exactly the same place are not in your favor.
The tilde before your 41 degrees says it all. So how precise can you get your timing, and to what end?
Living in an area that has paved, (and unpaved, for the scrambler riders) roads to 12000 foot elevation, I like to have the option of running a more advanced timing.
The lever lets you listen to the engine and run at the most appropriate timing for current conditions.
In other words, anything close is probably good enough when timing the mag, with a few degrees advance left in the lever for high elevation.
JMO JR
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/05/19 2:29 am

Originally Posted by Jerry Roy
So how precise can you get your timing, and to what end?
The answer to Part A of your question is, ~+/-0.1 degrees. I'll come back to Part B in a minute.

Further to your point about listening to the engine, when I'm leaving a slow corner and am maybe one gear too high I can hear the engine rattle so I quickly pull the magneto lever "somewhat" toward me, the rattling stops, and I continue accelerating. After a few seconds when the engine has built up some rpms I then I push the lever back to its fully advanced positions. Although I have the lever marked with a scale, when on the road I always precisely know two, and only two, positions of the lever: fully advanced, and "somewhat" less than fully advanced.

Back to Part B. Without any measurements one learns what positions of the magneto, choke and throttle work for starting a given bike, so in that sense a measurement like in my previous post is irrelevant. However, for me, at least, it's useful information to know that ~45% retard has the same result as an ATD would. Any "run-to-run" positioning variation for starting doesn't matter since I estimate that to result in a timing variation of only ~+/-2-deg.

Not that it matters because there are only three positions of the lever I care about when going for a ride (starting, fully advanced, and "somewhat retarded"), but there is actually very little variation in a Bowden cable pulling against essentially no resistance. So, if I do move the lever to one of the marked positions I'll get very close to the same value of advance every time.

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/07/19 4:31 pm

Jetting has been on hold for few days because I developed a cough that finally is respond to drugs. But, the coughing is greatly reduced by not talking, and since I don't talk to myself in the garage, I did manage to get some work done.

In addition to checking the points, setting the timing to 39.0°, "calibrating" the magneto advance lever, and re-installing the Amal 1036 (to which I added extended pilot and idle screws to make adjusting them easier on this LH carburetor), I caught up on the routine maintenance items of lubing the chain and all the cables. Also, the front brake was reluctant to return to its full-off position so since the bike was on the lift anyway I removed the wheel and found one of the two operating spindles (it's an Eddie Dow TLS) was stiff. It only required cleaning and greasing both spindles to make the operation smooth as silk.

Following up on an idea triggered by something gregg-k wrote last week, I designed a self-contained unit to bolt in place of the tach drive to allow checking the timing with a strobe. Whether or not it is useful in practice remains to be seen. And for that to happen I'll first have to make it. However, a step in that direction was the delivery yesterday of a 6"-dia. circular protractor.

In 1977 Harley-Davidson created their version of the cafe racer for its intended audience, the XLCR. Forty-two years later, with rearsets, RRT2 kickstart quadrant, low handlbars, small alloy tank and single seat, this Gold Star is now my version for its intended audience, the OMCR (Old Man Cafe Racer).


Attached picture Competition_OMCR.jpg
Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 05/07/19 4:50 pm


Funny, while it looks like an XLCR in some ways, the riding position I imagine for this bike looks like it might be an OMDM (an old man's Ducati Monster) I have an OMDM. Don't you have one, too?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/07/19 5:23 pm

Originally Posted by NYBSAGUY
this bike looks like it might be an OMDM (an old man's Ducati Monster)
Indeed, thanks to the relative positions of the handlebars, seat, and footpegs it feels very much like my Ducati Monster.


Attached picture Competition_OMDM.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/08/19 7:08 pm

I'm still not feeling quite 100% so I'll give the drugs another day or two before taking the bike on the road, but I couldn't force myself to wait any longer to try to start it. First, even though I had lubricated the clutch cable sometime within distant memory, lubricating it a couple of days ago made a very noticeable difference. I highly recommend people do so even if they think their cable is presently fine.

The bike started immediately on the DocZ and ran without any of the previous nonsense below 3000 rpm. I made two laps of the driveway then adjusted the idle screw and pilot mixture (which, unlike before I adjusted the float, now responds to the screw). The extended screws I switched to made making these adjustments a lot easier (again, it's a LH carburetor so the screwdriver has to reach under the tank and find the slots in the vibrating screws).

The photograph shows the Gold Star's current "dashboard." The analog gauge on the tach should go from 1-2 V for AFR 10-20 but as I had previously determined with a power supply and voltmeter it is a bit off at end of the range. The bike wasn't running when I took the photograph so with the AFR>20 the meter should be pegged at 2.0 V, but this imprecision doesn't matter since ~10-14 V is the only range of interest. Anyway, whether having this analog display is useful remains to be seen once I take it on the road.


Attached picture Competition_dashboard.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/12/19 12:29 am

A cough I developed over a week ago has finally relented enough that today I made my first post-retiming jetting run.

By accident I discovered an undocumented "feature" of my Innovate LM-1. On the last run a week ago the display had gone blank for a few seconds but it continued recording. I checked the battery and it still had 30% capacity but I replaced it anyway with one that tested 100%. Along with that undocumented feature of display blanking with a low battery, today a 16-segment bar graph appeared across the bottom of the screen which is a documented, but forgotten-by-me, feature. Apparently, it needs full battery power to be activated.

The bar graph provides an analog display of the mixture, with the middle at stoichometric λ=1 (AFR=14.7 for gasoline). Although λ is a "better" way of expressing mixture strength, especially for mixed fuels, I prefer to think in terms of AFR. In this case the display goes from lean >19.4 at the left to rich <10 at the right, so the desired ~12-13 for maximum power will have ~3/4 of the bars displayed.

The bike was a bit rich at full throttle, but behaved way better than previously. Actually, other than at full throttle, if not for the damn AFR gauge I might think the jetting was nearly perfect.

It ran well as I left the neighborhood with no hesitation on acceleration so the present #3.33 cutaway seems good. The first graph shows the AFR was ~13 (purple curve) at a little over 1/8 throttle (the red curve is the throttle opening, with full throttle 1.5 V).

The second graph shows that at ~1/3 throttle the AFR was ~14.5 so perhaps the needle could stand to be raised one notch (it's currently on the top notch). However, I won't alter it until I get the main jet worked out.

Once I reached the larger road there's a ~1/4-mile uphill stretch where if I time the traffic right I can give a bike full throttle for a few seconds for a crude check of the main jet. The bike stumbled from a too-rich mixture and as the third graph shows during that interval where I held full throttle for 3.5 sec. the AFR dropped to a very rich 9.2.

The bike idles well, but so far I've been too chicken to rely on that so I blip the throttle regularly when at the one stoplight on my jetting route. Also, I've become so reliant on the DocZ that I'm not sure I would even remember how to kick start it should it die at that light.

When I got back I adjusted the idle mixture screw for maximum rpm, which turned out to be an AFR of ~14, and then in preparation for the next run I dropped the main jet to 290 (it was 320). The next run should determine whether the 2-stroke spray tube results in too much depression for the .106 needle jet to handle. However, it was really well behaved other than on that full-throttle test so I'm optimistic that the right main jet may be all it needs at this point.

The tank is as empty as I'm comfortable with, and the granddaughters arrive in less than an hour for a sleepover, so there's no time to get more fuel plus make another jetting run today. Finding time tomorrow morning will be a problem as well, for reasons I don't remember...


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Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 05/12/19 3:29 am

Getting close..
Posted By: 998John

Re: Correct needle for 1000-series Concentrics? - 05/12/19 3:09 pm

This is a quote from http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter

"Triumph Triples use an angled spray tube cutaway from the mid point of the spray tube, rather than right across, as in the 2 stroke version. 2 Stroke and 4 Stroke bodies are not interchangeable and will not run correctly if used on the wrong type of engine."

Exactly what is the difference in the bodies that would not be interchangeable?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/12/19 3:56 pm

Originally Posted by 998John
Exactly what is the difference in the bodies that would not be interchangeable?
In a sense, this entire thread is about that question. The one, undocumented, difference that your quote from the Amal site could be referring to is the restriction in the compensating air passage of 2-stroke bodies.

There seems to be enough interest in Concentrics on Gold Stars that my goal is to see how close I can get with jetting using the 2-stroke spray tube and an unaltered 2-stroke body. Working toward this goal has taken me to the flow bench, milling machine, lathe and TIG welder so I'm approaching it with a fair degree of seriousness.

I've already drafted a 5-page "instruction manual" explaining how to jet a 1000-Series Concentric, that's just waiting for me to plug in the final numbers. However, if I fail to get clean running across the entire range of throttle settings with the current basic configuration, there will be two additional sections on drilling out the air passage and swapping spray tubes.

Posted By: 998John

Re: Correct needle for 1000-series Concentrics? - 05/12/19 4:50 pm

MM, a good moniker for you would be 'Bulldog'. Your tenacity is unmatched. Can't wait to see you instruction manual.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/12/19 11:03 pm

Originally Posted by 998John
Your tenacity is unmatched.
After giving a Russian scientist a tour of the research laboratory I had assembled over the course of my career he said to me, in the heavy accent and conspiratorial tone of a KGB agent, "With your facilities there are no secrets Mother Nature can keep from you." My approach to motorcycles is the same. A plaque a group gave me at the time of 'The Art of the Motorcycle' says "Erwin Rommel Award: For Aggressiveness and Tenacity in Pursuit of Motorcycle Avocations."

Well, today was a disappointment, with me having to be rescued by my wife 5 minutes into a jetting run without even having made it out of the neighborhood. The run started out great, with the first graph showing a 13-sec. stretch as I motored down the street at 3000 rpm (the black curve reads 2x too high) with the throttle barely cracked open (0.05V/1.5V = 0.033 throttle). As can be seen the AFR is on the rich side at 11 so maybe the pilot mixture is still too rich. If not that, the slide.

Unfortunately, things started to go bad beginning around 2'45" into the run. Misfires result in unburned oxygen in the exhaust, causing the sensor to spike as if it were lean. As can be seen in the second graph, during the same 13-sec. interval there were at least 9 misfires. However, the curve makes things look worse than they felt since the engine was at ~3-4krpm so in 13 sec. it fired ~400 times which means it didn't misfire 98% of the time.

Less than 30 sec. later it got even worse, as shown in the third graph covering the same 13-sec. interval. The number of misfires doubled. Within another 30 sec. after this graph ends the misfiring increased further, it backfired a few times, and I coasted to a stop. Because of the increasingly-bad behavior I probably was doing less than 15 mph during the final 30 sec.

This carburetor problem has 'ELECTRICAL" written all over it in flashing neon letters so back up on the lift it goes. Two steps forward, one step back. Sigh...


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Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 05/13/19 1:22 am

I should add a quick note, lest the crowd think that MMan is bullet-headed physicist, incapable of having fun.

Some of you have joined us on our adventures with various friends in Ireland (including, most notably, Chaterlea25, one of the organizers), at the Munster Rally, aka, the Irish National Rally. But there's more. As his co-conspirator on the Art of the Motorcycle exhibition, it fell to me to draw up a guest list for the opening banquet of the exhibition at the Guggenheim in Bilbao, Spain. MMan and I imagined a perfect invitation list, and top of that list was Giacomo Agostini, who at that time was working with the newly-revived MV factory, in Italy. So we invited him, and he accepted. Of course we sat him at our table, and he was as brilliant and charming as you can imagine. Agostini regaled our table for the evening with stories of his adventures, his racing career, and his epic duels with Mike Hailwood at the IoM TT. It was a motorcycling moment, never to be forgotten..
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/13/19 4:51 am

Originally Posted by NYBSAGUY
at the Munster Rally, aka, the Irish National Rally..



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Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/15/19 2:53 am

Fool me once, shame on the timing pinion. Fool me twice, shame on me. Fool me three times, ... well, geez, I hope not.

I don't know why the Gold Star backfired, since when it died the timing was at 9.5-deg. ATDC. That's where it should be, isn't it?

Anyway, just in case it isn't I removed the magneto from the bike to lap the pinion to the taper. In doing so I found that the lock washer inside the pinion was wedged tight enough that I had to tap it out with a drift from the other side. Perhaps this caused much of the torque on the nut to be spent expanding the washer against the wall rather than tightening the pinion onto the taper. I don't know if that was some, all, or none of the problem but I put the washer in the lathe and removed a few thou. from the OD so now it drops into place in the pinion.

I removed the armature from the body and then lapped the pinion onto the taper using Clover grinding compound. Now both tapers are uniformly grey. Everything is clean and ready to reassemble so I'll do that tomorrow, remagnetize it, and hope to have it installed and timed before guests arrive who will slow progress for the next few days.


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Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 05/24/19 12:28 pm

Its getting close to another Sunday, is it done?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/24/19 1:48 pm

Originally Posted by gavin eisler
Its getting close to another Sunday, is it done?
Despite the delay due to the roadblock Gordo placed in my way, compounded by the scandal uncovered in BSA dynamometer room (known in the U.S. as 'Dynogate' and in the UK as 'Dynexit'), rest assured it will be done by the end of Sunday, as promised. [*]

[*] The magneto has been back on the bike, and timed, for nearly a week so it's a matter of coordinating my schedule with my wife's for the next road test. Not that the pinion could possibly slip on the shaft again, but having the pickup truck on standby seems prudent.
Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 05/24/19 4:27 pm


Sunday evening can't come soon enough. We await (good) news with breaths bated.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/24/19 6:27 pm

Attacked by Gordo on one side, and Gavin & NYBSAGUY on the other, I'm feeling the heat... no, wait, the heat is because I forgot to turn the A/C on.

This morning I fabricated a universal mount for the Innovate's control box that also makes the display easier to see, checked over everything and, as far as I can tell, it's ready to go. The next window of opportunity for a jetting run is about two hours from now so in the mean time I'll have lunch, fill the tank, fire it up, and take a few laps of the driveway to make sure it's ready to jet.[*]

[*] It passed the driveway test so is ready for a jetting run.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/25/19 2:18 am

Because of scheduling I only had time for one run today, as the sun was dropping toward the horizon. The AFR drops to 10:1 under full throttle so the main jet is still too big. Despite that, the performance was spectacular under all conditions, including full throttle. I love the Ducati Monster-like way it is set up. I'll drop the main jet a few sizes and take it out again in the morning. I hope to have time for a few runs before the granddaughters descend for a sleepover.

The current main jet is 290. To decrease the current 10:1 AFR under full throttle to get it to 12:1 should require dropping the main jet to 10/12 x 290 = 241.7. I looked but don't have a jet that size in my cabinet so I'll use a 240. That should give me 290/240 = 12.08:1, which will have to do.

I might have mentioned this before, but Competitions were configured with an SCT and forward pegs but mine came to me with rearsets. I substituted an RRT2 kickstart spindle to get the lever away from my shin but didn't disassemble the gearbox to swap cams so it shifts like a Triumph. Although I have no trouble shifting my Triumphs like Triumphs, there must be something about the Competition's BSA essence that forces me to have to think whether its up for up, or up for down.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/25/19 9:58 pm

Originally Posted by Magnetoman
The current main jet is 290. To decrease the current 10:1 AFR under full throttle to get it to 12:1 should require dropping the main jet to 10/12 x 290 = 241.7. ... I'll use a 240. That should give me 290/240 = 12.08:1,
After looking at today's results, which I'll discuss momentarily, I looked again at yesterday's, shown in the first graph. The fat green line shows where an AFR of 9.4 would be. Note that I was at full throttle for only ~2 sec. so it's possible the thin green line would have reached that value in another second. Make a mental note of that.

OK, turning to today's results, and remembering that maximum engine power should be achieved when the AFR is in the range ~12-13, the second graph shows that with it held at ~1/8 throttle the AFR was 12.3:1. So far, so good.

The third graph shows that at ~1/3 throttle, where basically every variable in the carburetor is contributing, the AFR drops a bit to 12.0:1. Still, so far, so good. However, the graph also shows that at full throttle it drops to 11.0:1 despite my calculation yesterday that it should have been 12.08:1. I'll return to this in a moment making use of the mental note you made.

The fourth graph shows that the second full-throttle run today resulted in a slightly higher 11.4:1. However, note that it took 2-3 seconds for the ratio to drop to that value.

I used 10:1 from yesterday's run to calculate that I should use a 240 main jet today. Referring back to the first graph, if instead I had been able to hold full throttle for 2 sec. longer, and if the AFR had dropped to 9.4 in that time, then today the AFR should have been 11.36:1 at full throttle, which it was. Within experimental error the calculation I did yesterday to arrive at 240 gave the correct answer. However the "experiment" I did upon which I based the calculation wasn't run for long enough to achieve the steady state AFR value.

In light of today's longer full throttle runs, and using 11.0-11.4:1 as the values they gave, changing to a 220 for the next run should give 12.0-12.4:1. The smaller main jet also will increase the AFR somewhat at partial throttle resulting in values at all throttle settings falling in the sweet spot of 12-13:1 that gives maximum power.

As an aside, the jetting I used yesterday and today felt perfect at all throttle settings and rapid changes in throttle positions. Without the Innovate meter I would have been happy with yesterday's 290 main jet, or with today's 240, even though it looks like 220 is the one to use. Also, all of these settings are rich compared with stoichiometric 14.7:1. If I were tuning for economy rather than performance I'm not sure I could achieve it across the range with the present 2-stroke spray tube. Certainly not with a .106 needle jet.


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Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 05/26/19 12:57 am

Nice job of logging your results.

I'm doing some tuning on a TR25 (BSA 250) for Bonneville on which I've just installed a TM34 mm Mikuni Flatslide. Yes, it's big, but I have my own inertia chassis dyno with Performance Trends Datamite hardware and software and I'm getting some very good results. But what I find, with a Megacycle X4 cam and porting along with RD springs, long intake manifold, and short exhaust straight pipe, I can get 12-13 AFR up to 1/2 throttle, and again at full throttle but only after about 6,000 rpm, as it goes rich from about 4,000 to 6,000 rpm. So I believe that due to reversion, AF ratios can change at different rpm, and it will be darn hard to get AFRs of anywhere close to 13 until the resonance of the intake and exhaust kicks in. Fortunately, I only have to pass thru that troublesome mid-range in 1st gear after which I can just keep the R's up as I'm only timed thru the 3rd mile.

So length and shape of exhaust and intake will influence the AFR more than one might expect.

Tom
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/26/19 3:26 pm

Originally Posted by koncretekid
length and shape of exhaust and intake will influence the AFR more than one might expect.
It's remarkable how well a simple carburetor, lacking the array of sensors and feedback control of EFI, does dealing with all the things that are going on.

Originally Posted by koncretekid
I have my own inertia chassis dyno with Performance Trends Datamite hardware and software
Over the past several years my right brain has repeatedly convinced me I need a Datamite setup like the one you have. But, every time my resolve weakens my left brain takes over and reminds me that I live in a suburban area. Although the population density is fairly low near me, even a short full throttle test pushes my luck with encountering random sheriff's cars, and anyway there aren't long enough stretches of good enough road with low enough traffic close to my house. So, for me to get any real use from a setup like yours would require loading everything up and driving a long way from town.
Posted By: Cyborg

Re: Correct needle for 1000-series Concentrics? - 05/26/19 4:57 pm

Originally Posted by koncretekid
Nice job of logging your results.

I'm doing some tuning on a TR25 (BSA 250) for Bonneville on which I've just installed a TM34 mm Mikuni Flatslide. Yes, it's big, but I have my own inertia chassis dyno with Performance Trends Datamite hardware and software and I'm getting some very good results. But what I find, with a Megacycle X4 cam and porting along with RD springs, long intake manifold, and short exhaust straight pipe, I can get 12-13 AFR up to 1/2 throttle, and again at full throttle but only after about 6,000 rpm, as it goes rich from about 4,000 to 6,000 rpm. So I believe that due to reversion, AF ratios can change at different rpm, and it will be darn hard to get AFRs of anywhere close to 13 until the resonance of the intake and exhaust kicks in. Fortunately, I only have to pass thru that troublesome mid-range in 1st gear after which I can just keep the R's up as I'm only timed thru the 3rd mile.

So length and shape of exhaust and intake will influence the AFR more than one might expect.

Tom



I wonder if there is something you can do to the pipe to reduce the reversion. I've been trying to wrap my head around the subject and my limited experience so far has to do with marine exhaust.

The HD folk use anti reversion cones, but this fellow has his doubts about them. http://www.nrhsperformance.com/tech_arcones.shtml

Here is more on the subject http://garage.grumpysperformance.com/index.php?threads/anti-reversion-exhaust-design.789/

Would some sort of bunsen valve work at 4 to 6K? .... I have no idea, but there is a fellow on this forum and he may know. If so, you could confirm its reversion. As for using a bunsen valve at Bonneville, the tech folk might decide you belong in a home rather than on the salt.

Sorry for the highjack OP.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/26/19 5:32 pm

Originally Posted by Cyborg
I wonder if there is something you can do to the pipe to reduce the reversion.
When the pipe is the right length the resonance is a good thing overall, although it can cause a rich mixture at intermediate settings. Anything done to kill that resonance also robs h.p.

This is a common problem with an Amal GP and 'twitter' silencer, simply dealt with by using a different needle. The "weak" 3GP6 needle that solves the problem has a longer straight section than the "normal" one so the straight section is still in the needle jet at intermediate throttle settings where reversion plus valve overlap causes the air to pass three times over the spray tube (on the way in, back out, and in again), picking up excess fuel.

In an ideal world, where Mikuni actually could supply all the needles in their catalog, you would figure out over what range of throttle settings you had a problem, translate that into the range of positions of the needle in the jet, and pick a new needle that had a flatter slope in that region than the needle you're currently using.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/27/19 12:29 am

Based on the jetting runs I've made so far it's best to sit at each throttle setting for at least 5 sec. to allow the AFR to settle on its final value. After installing a 220 main jet I made two runs today with that in mind. The first established that the 220 does the trick. It also provided data at lower throttle settings.

I printed the output in regions where I had held the throttle at constant value for at least 5 sec. I then normalized the throttle voltage readings to the full-throttle 1.5 V value and marked that on the eight sheets of output. I then measured the AFR at those positions. Plotting all of this showed I needed more data between idle and half throttle to know what is happening in that important region. After a second run with that in mind I ended up with 30 data points between idle and half throttle, and another two at full throttle.

There's scatter in the data[*] but a smooth curve drawn through AFR vs. throttle opening starts out at 14.2:1 at idle, steeply drops to ~11.5:1 just before 1/8 throttle, steeply rises back up to ~14:1 by 1/4 throttle, then slowly drops to ~13:1 before 1/2 throttle. The full-throttle value is ~12.2:1.

Basically, there's a narrow Gully of Richness between idle and 3/16 throttle that I'll blame on the cutaway. It's currently 3.33 so it could benefit from being machined to be a full 3.5.

Between 3/16 and 1/2 the AFR drops from 14 to 13, which is rich, but somewhat "economically rich." This is where any bike spends most of its time so it doesn't hurt to have the ratio closer to stoichiometric. "Powerfully rich" is available at larger throttle settings, where it's needed.

On the second run today I paid more attention to the "feel" of the bike and not the display of the AFR meter, and it feels great. I'm inclined at this point to remove the pipe with the sensor and return the bike to full riding condition. When I feel sufficiently motivated I can remove the slide and slice a little more off it to deal with the Gully of Richness. But, I'm in no hurry so I'll let this decision sit for a few days.

[*] While I can read the AFR from a graph to within 0.1, when I plot data from different times on a given run, or from different runs, the graph ends up with scatter of ~+/-0.5 at a given throttle setting. Hence, a lot of data is needed to determine the overall trends.
Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 05/27/19 12:30 am

The reversion I'm experiencing is partially by design, to enhance horsepower at the uppermost range of my rpm, approximately 8200 rpm, and it seems to be working. Although my dyno is not calibrated properly because I can't determine the actually thickness of the dyno wheel, it tell me that the little 250 is developing 27-28 horsepower. It has already set a record of 100 mph at Loring, Maine.

I can avoid the reversion problem by keeping the throttle at 1/2 to 3/4 throttle, so the needle jet and the needle are pretty well suited, but I need to keep accelerating and that means I have to go WOT (wide open throttle) as soon as possible. At WOT, the needle is no longer in play, so the mixture is correct at about 6,000 to WOT, but not at the 4-6,000. So this is not a road bike but is dedicated to land speed racing.

Tom

P.S. I just finished building an enclosure to try to mitigate the noise issue, as I too am in a residential area. So far, so good. I'll post a few photos in a subsequent post.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/27/19 12:38 am

Originally Posted by koncretekid
P.S. I just finished building an enclosure to try to mitigate the noise issue, as I too am in a residential area.
I misunderstood. I thought you meant you used the accelerometer in the Datamite to calculate the h.p. from the performance on the road. I'm afraid there's no way I could adequately muffle an actual chassis dyno to get away using it in my neighborhood I cringe at what evil thoughts the neighbors must think about me every time I start a Gold Star.

p.s. The developer who built ours and three other houses some years ago made the four of them into their own homeowner's association with deed restrictions that strictly prohibited motorcycles. This obviously was a deal breaker when we were looking but the real estate agent wanted the sale badly enough that she managed to convince everyone to sign a document dissolving the association. I'll bet they rue the day they signed that paperwork.
Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 05/27/19 1:24 am

https://share.icloud.com/photos/0ZnerKnBr0mgEGfEAmgobjhpA
https://share.icloud.com/photos/0n3Vn_Viz5ROzORgLWa-sGXZw
Test: photo from my ICloud account. This is a photo of my dyno enclosure, staggered studs with 3 layers of 1/2" sheetrock and a large exhaust fan. The wife says it's better, but still loud.

I have a Postimage account, but I need to learn how to transfer photos from my Iphone to my MacBook so I can post them to Postimage. I need a techie!
Posted By: Cyborg

Re: Correct needle for 1000-series Concentrics? - 05/27/19 1:38 pm

You could just go low tech. Assuming you have your email set up on your MacBook.... just take the photo with the phone and email it to yourself. No doubt there is a proper way, but for the odd photo, it works fine for digitally challenged old farts.
Posted By: koncretekid

Re: Correct needle for 1000-series Concentrics? - 05/27/19 10:48 pm

I think I have the solution. When the Macbook is synced with the ICloud, the photos do show up in my IPhotos. Then I export them to a site in Pictures I call forum photos and I reduce the resolution. Then I can import them into Postimage, click on the share button, copy the link to "forum hotlinks", then post the link here and it shows up, I think.
[Linked Image]
and another one with the TR25 on the Dyno.
[Linked Image]
And one last one showing the old leaf blower hooked up to blow air directly on the cylinder head.
[Linked Image]
MM - sorry for the hijack!
Tom
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/28/19 4:18 am

Originally Posted by koncretekid
MM - sorry for the hijack!
Not at all. Your setup is very interesting and not unrelated to the "road dyno" I've been using to sort out my jetting.

Originally Posted by Magnetoman
When I feel sufficiently motivated I can remove the slide and slice a little more off it to deal with the Gully of Richness. But, I'm in no hurry so I'll let this decision sit for a few days.
I managed to let that decision sit for all of 12 hours before I needed answers. So today was a busy day on the neighborhood streets.

I made a run to fill in data between idle and 1/4 throttle and found the Gully of Richness deeper than I had thought so I decided to increase the cutaway. A careful measurement showed it to be currently the equivalent of a #3.28 so, not having any idea how much an effect I was going to see on the AFR, I played it safe, decided to increase it only to #3.5. I already had the jig, tilted it to the proper 15-deg., and ended up very close at 3.49.

With the #3.49 in place I made another run and found the depth of the Gully had decreased by about an AFR of 1, but was still a too-rich ~10.5. So, I removed the slide and turned it into a #4.

With the #4 in place I made another run and found the depth had decreased to ~12.2, i.e. increasing the cutaway by half increased the AFR by ~1.7. Of course, the cutaway has an effect over a range so the AFR also increased at 1/4 throttle to be too-lean.

Since 1/4 throttle is in needle jet territory the last thing I did this afternoon was pull the carburetor yet again and raise the needle one slot to be ready for tomorrow.

I'm getting pretty fast at making carburetor modifications. I can have it off the bike, the slide removed and reinstalled, and it back on and ready to go in just over ten minutes. Twelve if I install the cap 180 degrees from where it should be, which is completely possible on this carburetor. If installed incorrectly it seems to work fine but the slide won't go quite to the top.


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Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 05/28/19 1:31 pm

Why not change the spray tube to the four stroke style to see what that changes.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/28/19 3:14 pm

Originally Posted by RPM
Why not change the spray tube to the four stroke style to see what that changes.
That's a reasonable question and I might end up doing that for one of two reasons: curiosity, or necessity.

My underlying goal is to determine if the basic 2-stroke Concentric body can be wrestled into submission for use on a Gold Star without making permanent or semi-permanent modifications, i.e. drilling out the compensating air passage or replacing the spray tube. If I succeed then the settings I find will allow future Gold Star owners to make the switch by simply substituting stock components.

Doing this is letting me learn more about carburetors than I otherwise could have no matter how many books or article I've read. The flow bench measurements I made a month or so ago let me determine the effects of both the spray tube shape and the air passage on the depression, which is something I've never seen written about before. Further, the flow bench showed that what has been written about the effect of the air passage is so simplified as to be essentially incorrect. Also, we all know that increasing the cutaway makes the mixture leaner (Amal says the effect is from 1/8 to 1/4 throttle), but I now have the measurements that show how much leaner for an engine with a lot of valve overlap (1.7 AFR units for 0.5 change in cutaway), and over what range of throttle settings. The latter turns out not to be a constant change, but a curve that extends from idle to a little past 1/4 throttle, with maximum effect a little before 1/8. That is, where Amal says the cutaway should just be starting to have an effect it already is a little past the point of maximum effect.

As for spray tube shape, Norton and Triumph both used non-"4-stroke" spray tubes so it's not obvious ahead of time that a flat-cut shape will be "best" for a Gold Star. If I don't run out of energy before I finish this exploration, and even if I get an excellent mixture across the full range of throttle settings with the 2-stroke body, I plan to change to a 4-stroke spray tube just to see what effect it has.

With luck, today's jetting run(s) with the needle raised by one slot should tell me it's possible to get an unmodified 2-stroke Concentric to provide good AFRs across the full range of throttle settings. Or, I may learn I need to slice a little more off the slide. Or, I may learn I'll have to swap spray tubes and drill the air passage.

My BB Gold Star has a (smaller) 4-stroke Concentric, my Catalina has a Monobloc, and I have a header pipe with oxygen sensor in it, so this may not be the last you hear from me about Gold Star carburetor settings and AFR...

Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 05/28/19 5:38 pm

Cutting the slide is permanent. Changing spray tube is not. I now know more about carbs from your work also.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/28/19 6:09 pm

Originally Posted by RPM
Cutting the slide is permanent. Changing spray tube is not.
That's true, but now my slide that started out as a stock #3 is identical to a stock #4, which I didn't have on the shelf. Having a mill makes up for my lack of an extensive inventory of 1000-Series slides. Despite my permanent change to that slide, If (when) I continue these experiments with a 4-stroke spray tube I now have a stock #2 and stock #3 to try, as well as the "stock" #4.

I would have faced the same situation with a 4-stroke spray tube if it turned out none of my slides I had when I started this (a #2 and two #3s) had the correct cutaway. Given the size of the jump in AFR when I went from a #3.49 to a #4, and that Amal supplied slides in steps of 0.5 for various bikes, there's a 50/50 chance I'll have to shave one of my current full-number slides when used with a 4-stroke spray tube.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/28/19 10:36 pm

Toward the end of my last run yesterday, the bike abruptly started missing badly below ~3000 rpm. It acted like a fouled plug that would clean up at higher rpm, but the plug looked fine when I got home. I changed it anyway. Also, since I've not been making use of the rpm signal I removed the pickup that was sitting on top of the magneto just in case a short had developed through it.

Today, it started out running just as badly at low rpm as it had yesterday. The symptoms began abruptly in the middle of a run yesterday, and since then I've changed the plug and had the carburetor off and back on again, so it strongly suggests an electrical issue. The timing doesn't seem to have slipped, as evidenced by the fact I can retard it through at least half the range at idle without the bike dying, but I'll definitely be checking this. Although the plug wire is 20+ years old, it has a stranded metal core and measures 1.2 Ω so doesn't have a break that the spark only jumps at higher rpm. The pickup seems fine as well (~15 Ω ). Also, the fact it still idles fine means the pilot jet or outlets aren't blocked.

Back up on the stand it will go. It can't be the magneto (which includes the pinion), but it can't see how it can't not be the magneto, either. I'll check the timing before I remove the magneto, but if that's not the problem I'll test it across the full range of rpm to try to identify the issue before doing a very thorough check of it.

And, if it's not one thing, it's another. Yesterday the Battery Tender I use to top up the 2.3 A-hr. battery for the Bosch sensor was fine. Today it has no sign of life. Sigh...

Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 05/29/19 7:08 am

Originally Posted by Magnetoman
.........And, if it's not one thing, it's another............Sigh...


And I thought this sort of stuff only happened to me. Stick with it MM, I am sure all will be well fairly quickly.

John
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/29/19 4:03 pm

Originally Posted by George Kaplan
Stick with it MM, I am sure all will be well fairly quickly.
Thanks for the encouragement. The situation with the Gold Star may sound worse than it actually is. I've only intermittently spent relatively little time on it so the cumulative time I've spent actually working on the bike (machining the slide twice, rebuilding the magneto, timing the bike, making jetting runs, etc.) the last month is probably less than eight hours.

On the Battery Tender front, I machined the heads off the four rivets "permanently" sealing it and tested the 4700 µF electrolytic capacitor. Since it was only ~600 µF I ordered a package of four new ones for $8.50 in the hopes that will fix it. Also in the hopes I can find where I put the other three capacitors if/when the capacitors go bad in my other two Battery Tenders. Electrolytic capacitors have a finite lifetime and are commonly the cause of power supply failures so there's reason to think a new one will fix the unit. Even at the full $8.50 for the package of four capacitors it's cheaper than a new charger at ~$40.
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 05/29/19 7:29 pm

Originally Posted by Magnetoman
<SNIP> tested the 4700 µF electrolytic capacitor. Since it was only ~600 µF I ordered a package of four new ones for $8.50 in the hopes that will fix it. Also in the hopes I can find where I put the other three capacitors if/when the capacitors go bad in my other two Battery Tenders. Electrolytic capacitors have a finite lifetime and are commonly the cause of power supply failures so there's reason to think a new one will fix the unit. Even at the full $8.50 for the package of four capacitors it's cheaper than a new charger at ~$40.

Odd MM: yours is the third instance I've heard of recently in which a Battery Tender has gone bad. In two of the cases it permanently damaged a battery which was only a few months old. .

... Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/30/19 1:26 am

Originally Posted by gREgg-K
Odd MM: yours is the third instance I've heard of recently in which a Battery Tender has gone bad. In two of the cases it permanently damaged a battery
I don't have date codes on mine but one of them is over 25 years old and another might be 20. In electrolytic dog years, that's pretty old. The output of mine after it died was only some number of mV so damaging the battery wasn't an issue.

I spent my garage time today making a special tool I thought about making last time (and the time before that), but I thought the job I did lapping the taper made it unnecessary. I don't know yet whether the problem is that the timing slipped again but, as the first photograph shows, the exhaust pipe and timing cover have to come off to do an accurate measurement to find out. But, what about a semi-accurate measurement?

The second photograph shows the breather, driven by the timing pinion, that also drives the tach. If the rotation angle of that breather could be measured with sufficient accuracy it, along with the opening of the points, would determine if the timing had slipped. Since access to the breather only requires removing the two screws that hold the tach drive this is a check that could be done quickly on the driveway instead of time-consumingly on the lift.

The third photograph shows the brass fitting I made to fit the slot in the breather, and the fourth photograph shows it installed the Al cover I made to be a snug fit on the inner ID of the timing cover as well as with the two screws. The cover has no detectible movement with respect to the timing cover.

The final photograph shows that the Mark I indicator I made for the tool determines the angle to ~1-deg (2-deg. engine). It still remains for me to "calibrate" the indicator by "locking" it at 19.5-deg. with the hold-down bolt after properly setting the timing and reinstalling the timing cover. The lock-down bolt also is used to remove play from the drive train prior to making a measurement (if I remember which way to turn it to remove, rather than add, play...).

Now that I have this tool made and ready for "calibration" I'm ready to remove the exhaust pipe and see if the timing slipped. If I had made this tool previously I could have checked the timing in just a couple of minutes and spent today working on the bike. However, in the future it will tell me to within ~2-deg. engine if it had slipped, which should be more that good enough for diagnostic purposes since it would have to have slipped by more than that to have a noticeable effect on the engine. Also, at some point I'll use the by-then-calibrated tool on the Catalina to see how universal it is, i.e. how accurately the slots for the tach drive are cut in different breathers.


Attached picture TimingTool01.jpg
Attached picture TimingTool02.jpg
Attached picture TimingTool03.jpg
Attached picture TimingTool04.jpg
Attached picture TimingTool05.jpg
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 05/30/19 12:51 pm

Absolutely correct about the life of electrolytic caps, especially in hot climates. I had no idea that your failed Tender was that old: the two that failed locally are less than a year old.

Nice work on that tool for checking timing of your magneto without having to dismantle too much. It's an excellent investment of time for future gains!

.. Gregg
Posted By: edunham

Re: Correct needle for 1000-series Concentrics? - 05/30/19 1:44 pm

I check the timing on my Velo and my Norton by using my positive stop TDC tool. My positive stop tools are home made and adjustable. The first time I set the timing on a bike I use the positive stop tool with a degree wheel. Once I have the timing set, I adjust the tool so that it is just kissing the piston at the firing point. I then lock the tool at that point. After that, to set or check timing, I just put the engine on the compression stroke, insert the tool, rotate engine till it stops against the tool, remove center screw from mag and use my continuity light. Rarely takes more than 10 minutes, unless I actually have to adjust the timing (timing cover has to come off then). I have a separate tool for each bike.

Ed from NJ
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/30/19 5:10 pm

Originally Posted by gREgg-K
the two that failed locally are less than a year old.
Mine are shaped like the model they now sell as Battery Tender Plus 1.25 A but the front panel is different as is the description of its features. So, the circuitry inside the ones they sell today is different than that inside my old ones. I think there were only a couple of models available when I bought mine; now their website shows 27.

Originally Posted by edunham
I check the timing on my Velo and my Norton by using my positive stop TDC tool.
That's a good solution, telling you if the timing is still good, or if the points are opening too soon (or too late, if they somehow could have slipped forward). But, my tool has a couple of advantages over a positive stop in the spark plug hole.

I painted the side of my cam ring over the ~180-deg. where the points are open, and have lines at the starting end of the paint (~40-deg.), 20-deg., and TDC. So, without having to raise the rear wheel using the Competition's non-existent center stand, or using a meter to detect when the points open, I can push the bike forward until the points are somewhere in the range between 40-deg. and TDC. Since I can estimate that position to maybe 5-deg. that value, along with the reading from my new tool, will tell me if the points have slipped. Since the only reason to do this check is if the bike has started missing badly, the timing will be off by more than 5-deg. so greater accuracy isn't needed to know whether the issue might be with a slipped taper, or if it probably lies elsewhere.

Another issue is that when diagnosing problems I like to have as much information as possible. If I had the rear wheel off the ground (best done on the lift to avoid crawling around on concrete) I could find TDC with a ruler down the spark plug hole, rotate the engine backwards, find how many inches BTDC the points open, and look up that value in a table to find degrees. In essence, my new tool does the same thing, but somewhat faster.

Another point is I cringe every time the piston comes against the hard stop of the relatively sharp end of the TDC tool. In addition to whatever the tip does to the top of the piston, it's like putting a lever a few inches long in the spark plug threads and hitting it sideways with a hammer. So, my procedure when the bike is on the lift has been to find approx. TDC with a ruler in the spark plug hole, set the timing disc to TDC, rotate the engine backwards to ~40-deg, and insert the tool. Then, since I know it will hit at 29-deg. if I had set the timing disc perfectly at TDC, I can rotate the engine slowly forward until it hits the stop relatively softly. I know that's 29-deg. with my TDC tool so I make whatever small adjustment is needed and then know where it will hit again on the ATDC side.
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 05/31/19 7:26 am

Originally Posted by Magnetoman
I cringe every time the piston comes against the hard stop


I have used hard stops on occasion too but I always cringe too even if I have crept up on it very gently.

However, if one didn't have a convenient tacho drive to utilise then going through the plug hole is not such a bad idea. A simple screwed in plug with a slider down the middle will indicate piston position quite well, certainly good enough for a check to see if the timing has slipped significantly. If one were worried about the slider/piston interface then make it out of plastic or put a plastic tip on it. I know most plug holes are at an angle to the bore but 30 seconds of trig will fix that.

John
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/31/19 3:55 pm

Originally Posted by George Kaplan
A simple screwed in plug with a slider down the middle will indicate piston position quite well, certainly good enough for a check to see if the timing has slipped significantly.
I'm quite happy with timing sticks. This link shows one I made for my Ariel.

The potential advantage of my "rotary timing stick" tool is that, if the breathers were made with reasonable uniformity, the same tool will work on all Gold Stars irrespective of the height of their piston crowns. Just the same, I'm now motivated to make a 10:1 timing stick today.

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 05/31/19 8:07 pm

Well, the problem is that the timing slipped yet again. I've never had this problem before but this time I'm going to lap the tapers much longer than I did before, and with finer grit. Then I'll use a torque wrench when attaching the pinion, which is something I've not done before. If that doesn't work, there's always the TIG welder...

Prompted by edunham's and George Kaplan's posts I made a bespoke timing stick much like the one I made a year ago for my Ariel. While visions of slipped pinions danced in my head, for the 'Competition' I made the stick with notches at 39-deg. and 20-deg. which, with TDC also found with the stick, allows for a good estimate the amount of slippage. Of course, the actual problem isn't to measure the amount of slippage, it's to eliminate it.


Attached picture TimingStick.jpg
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 05/31/19 9:22 pm

You can bell mouth a taper when lapping. If the grit is too evenly spread, the OD cuts more than the ID.
Posted By: edunham

Re: Correct needle for 1000-series Concentrics? - 05/31/19 11:34 pm

Every time I have had a taper on mag that didn’t hold, it was either because of something I did or didn’t do the last time I was in there, or because something else was wrong. Washer missing on the advance gear, that sort of thing. My only point is that before you go all medieval on the taper, make sure it wasn’t something simple.

Ed from NJ
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 05/31/19 11:45 pm

I can't say that I have known a taper to have slipped like that, especially after having been lapped by a careful practitioner such as yourself, MM. I wonder if the female taper is bottoming out somehow, preventing the mating surfaces from contacting fully? I've seen this happen if the small end of the male taper is slightly large, and/or extends too far into the pinion's female taper.

I've seen several armatures that must have had this problem, because someone had cut back the small end of the male taper. Some manufacturers used to include a thick washer between the pinion seat and the securing nut to ensure the nut did not bottom out on the start of the male taper. May not be your issue, but worth checking.

.. Gregg
Posted By: chaterlea25

Re: Correct needle for 1000-series Concentrics? - 06/01/19 12:42 am

Hi MM,
Quote
Well, the problem is that the timing slipped yet again. I've never had this problem before but this time I'm going to lap the tapers much longer than I did before, and with finer grit.


Selective memory loss ???? LOL (your Ariel)

If Ed and Gregg's comments are not the problem
I'll bet the magneto drive shaft is turning relative to the armature, I have come across this problem a number of times before
I have seen more than a handful of rough tapers that give enough grip to drive a magneto without trouble
perfection is not needed,


John

Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 06/01/19 2:05 am

Originally Posted by gREgg-K
I wonder if the female taper is bottoming out somehow, preventing the mating surfaces from contacting fully? I've seen this happen if the small end of the male taper is slightly large, and/or extends too far into the pinion's female taper.

<--- snip --->

Some manufacturers used to include a thick washer between the pinion seat and the securing nut to ensure the nut did not bottom out on the start of the male taper. May not be your issue, but worth checking.
I thought something similar. Either the pinion taper may be bottoming out (very hard to see with the magneto in place) or the nut bottoming on the shoulder of the taper / washer too thin. I think MM mentioned earlier that the washer o.d. was previously a little large and was jamming in the pinion.
Time for the bearing blue on the next reassembly?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/01/19 3:17 am

Originally Posted by Magnetoman
Well, the problem is that the timing slipped yet again.
That statement turns out to be incorrect, which is entirely the fault of edunham and Goerge Kaplan because:
Originally Posted by Magnetoman
Prompted by edunham's and George Kaplan's posts I made a bespoke timing stick
If those two hadn't tricked me into making the timing stick I wouldn't have inadvertently left it on the 20-deg. BTDC notch when I looked at the points, and incorrectly reported the timing had slipped. I hope they are ashamed of their mistake.

Originally Posted by chaterlea25
Selective memory loss ???? LOL (your Ariel)
No, the Ariel's issue is burned deeply into my long term memory. However, in that case the points plate slipped on the shaft. It's the pinion slipping on the taper that I've not experienced before. But, as I wrote above, it didn't slip this time, so the problem is something else.

The misfire problem had developed fairly suddenly after more than ten minutes into a run, but it only happened at fairly low rpm, going away at higher rpm as if the spark plug cleaned itself. So, after I pulled the magneto from the bike I installed my largest pulley and put it on the long term tester. The problem quickly revealed itself to be intermittent sparking between the spring and the cam, as shown in the photograph.

The fundamental source of this problem is the taper. That is, when I had it apart a few days ago I didn't think about it as rebuilding the magneto, I thought about it as just lapping the taper. So, I didn't take sufficient care when I reassembled it after the lapping.

OK, tomorrow a complete, careful magneto rebuild is on the agenda.


Attached picture CamLobeSparking.jpg
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 06/01/19 7:55 am

Originally Posted by Magnetoman
[quote=Magnetoman]] entirely the fault of edunham and Goerge Kaplan


I shall forever hang my head in shame .

John

Posted By: GS 4112

Re: Correct needle for 1000-series Concentrics? - 06/01/19 3:55 pm

Went through a taper slipping problem years ago. Problem ended for me when I started using a torque wrench to tighten using 20 ft lbs.
I use my old Bultaco spark plug hole vernier for TDC which is spring loaded and works great for finding TDC.
Charlie
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/02/19 5:22 am

Hoping to avoid any issues I took great care rebuilding the magneto today, including using new points. I'm not in a great hurry because my daughter has the pickup through Sunday for a dressage event and I want it here as backup until I'm sure I have the issues sorted out.

After rebuilding the magneto I put it on the long term tester to make sure all was well, but there wasn't any spark. I reduced the gap, tried again, and everything was fine. I then magnetized the magneto, put it back on the tester, returned the gap to 5 mm and it sparked like it should. I mention this to point out that removing the armature and replacing it reduces the output. Only remagnetizing it will return it to the as-new performance.

My electromagnet is powered by the nominal 220 V from a socket in the garage, but the voltage on any given day or time varies. Today it got the magnet to 82.5 kA-turns, which is ~18% higher than the upper limit recommended by Lucas (38% greater than the lower limit). Unlike a tachometer, exceeding the recommended upper limit isn't bad since the Alnico simply sheds anything in excess of what it can store.

The spring for the points comes very close to the cam so I set up a strobe in order to follow the motion as the points plate slowly around to look for possible contact. It comes closer than I'd like but there's nothing to be done about it.

The sound of the spark changes slightly when it follows different paths so it's hard to tell if that is what is happening, or if it's missing. So, I hooked up a HV probe to my analog oscilloscope to watch for signs of missing. An iPhone has its limits when trying to take a photograph like this but it shows the principle. The oscilloscope triggers off a pulse and with the time base set at this sweep speed I can see it and the following three pulses. This is constantly repeated so if the magneto failed to fire during the time I was watching it would be obvious in the shape of a dropped pulse.


Attached picture MagnetoTest01.jpg
Attached picture MagnetoTest02.jpg
Attached picture MagnetoTest03.jpg
Posted By: chaterlea25

Re: Correct needle for 1000-series Concentrics? - 06/02/19 10:46 pm

Hi MM,
OK, a not so serious problem so
I am not a fan of the steel back plate points which often display the problem you encountered
A diamond coated needle file (LIdl or Aldi and probably Walmart) will file the hole in the spring to elongate it where it is clamped by the securing screw moving the curve away from the cam ring

John
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/03/19 12:27 am

Originally Posted by chaterlea25
Hi MM, I am not a fan of the steel back plate points which often display the problem you encountered
I have several older brass points plates I could revive, but the springs on them seem just as close. But, if you continue reading a few more paragraphs, I've come across another issue.

I'm not a fan of digital oscilloscopes, although they do have their uses. The first photograph shows a string of 41 sparks over 1.2 sec. (≈4100 rpm engine) without a miss, and watching for several minutes convinced me the magneto isn't missing. In case it's relevant, I've run the new set of points on the long-term tester at 2000 rpm for about an hour. I then moved the magneto to my modified distributor tester to check the timing. There, the plot thickened.

As the second and third photographs show, this tester lets me determine the timing of the spark to better than a degree. This is particularly useful for twin magnetos to see if the sparks are exactly 180-deg. apart (or whatever, for a V-twin). However, it's also useful to see if the timing jumps around due to issues with the points.

Unfortunately, as the fourth photograph shows, at higher speed the timing advances by ~5-deg. (10-deg. engine -- nb. from the tester's point of view the rotation is CW). This happens over a fairly narrow rpm range that I judge to be ~2000 rpm (the battery in the tester's tachometer died and I don't have a replacement). That is, below that rpm the timing has the same value as it does at lower rpm, but above it the timing advances by ~5-deg. The exact rpm where this happens isn't important, but the fact it does happen is.

I tried adjusting the points to give them a somewhat different gap but got the same result. It's not an artifact of my tester since I can watch the pinpricks of light from the points at high rpm and see them move to a less advanced value when I turn the rpm down. For the timing to advance the points have to open sooner and at the moment the only speed-dependent mechanism for this that comes to mind is if somehow the initial slope of cam (or a slight bump) is such that beyond a certain speed it "launches" the rubbing block rather than it continuing to follow the cam to the place where it should open.

I have to find the source of this problem and fix it because I certainly don't want the timing to suddenly go from 39-deg. BTDC to 49-deg. when I exceed ~4000 rpm.


Attached picture MagnetoTiming01.jpg
Attached picture MagnetoTiming02.jpg
Attached picture MagnetoTiming03.jpg
Attached picture MagnetoTiming04.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/03/19 2:55 am

Interesting..one wonders whether this is repeatable on other magnetos of similar points operation? This might have been a design issue that was never realized?
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/03/19 5:10 am

Originally Posted by Kerry W
Interesting..one wonders whether this is repeatable on other magnetos of similar points operation?
I have another Lucas Competition magneto on my Catalina but as you can imagine I'm not inclined to remove it for measurement. Tomorrow I'll look through my inventory of rusty parts in the hopes I might find another cam ring I could substitute for comparison.

The problem with having too much instrumentation is it only highlights problems, it doesn't provide solutions. Sigh...
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 06/03/19 11:43 am

Originally Posted by Magnetoman
I'm not a fan of digital oscilloscopes, although they do have their uses.

Hi MM, may I ask why you dont like them?



Originally Posted by Magnetoman
For the timing to advance the points have to open sooner and at the moment the only speed-dependent mechanism for this that comes to mind is if somehow the initial slope of cam (or a slight bump) is such that beyond a certain speed it "launches" the rubbing block rather than it continuing to follow the cam to the place where it should open.


Could it be the spring that is letting this happen, too weak (or too strong)? Or a combination of the cam profile and spring, could there be some resonant frequency for the cam profile/spring combination at a certain rpm range?

My comments are just really thinking out load rather than knowledge and experience with this issue. I will be interested to see the cause of this.


John
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 06/03/19 1:16 pm

I've seen this phenomenon on my test bench as well. Sorting it out usually requires adjusting the tension of the contact breaker spring using a fixture of the type described by Lucas in their repair manuals.

It seems more likely to happen with the later/so-called "Low Inertia" fabricated steel assembly than on the older brass type.
.. Gregg
Posted By: triton thrasher

Re: Correct needle for 1000-series Concentrics? - 06/03/19 1:35 pm

If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base, you get that sudden advancing effect when rpm rises.
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 06/03/19 1:37 pm

It might be an optical illusion, but it seems to me that in the photo copied below, the contact breaker's anti-fatigue feature is assembled incorrectly:

[Linked Image]

It should be inserted between the spring leaf and the post on the contact breaker, and curving inward toward the center of the mag. The photo appears to show the feature between the head of the screw and the spring leaf, rather than under the spring leaf.

As MM says, those "low inertia" contact breakers can be a pain to assemble without having the spring leaf shorting against the cam ring. Shorting that way did not cause loss of spark with the earlier brass type because the spring leaf connected to the brass platform, but it caused leaf wear nonetheless
.. Gregg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/03/19 4:19 pm

Originally Posted by George Kaplan
Hi MM, may I ask why you dont like them?
Digital oscilloscopes process the input in order to display waveforms, in multiple colors, that look great. Unfortunately, this means pesky features like transients usually are eliminated, which is often where clues to misbehavior lie. With a fast analog 'scope like the Tektronix 2465B, whose screen I showed in a recent post, what you see is what you got.

As an aside, in inflation-corrected dollars that Tektronix 2465B analog oscilloscope would sell new today for around $14k whereas their roughly-equivalent digital oscilloscopes sell for only 10-20% of that. The move from analog to digital wasn't because digital is better, it was largely driven by competition from manufacturers offering digital 'scopes with color displays, clean-looking signals, and automatic setup of triggering at a push of a button for a lot less money. Since that satisfied the needs of the majority of customers, it killed analog. It's also why you can find a 2465B on eBay for a lot less than $14k.

I'm not saying digital oscilloscopes aren't useful, because they are. Including three portable, battery-powered units I have four of them. One isn't much larger than the size of a credit card and, although it is very limited in what it can do, it's been with me on at least three trips to Ireland where it collected useful data on several magnetos. Also, a very useful feature of my benchtop digital 'scope is its ability to display an FFT, which is a crude, but quite useful, substitute for a spectrum analyzer. A digital oscilloscope is way better than no oscilloscope, but for troubleshooting fast transient phenomena I'd hate not to have an analog 'scope.

Originally Posted by George Kaplan
Could it be the spring that is letting this happen, too weak (or too strong)? Or a combination of the cam profile and spring, could there be some resonant frequency
The spring is rivetted to the points so I have no control over its strength. I can imagine why the points might open too late at higher rpm, but I'm struggling to find a reason why they open too early. The fact that the opening position doesn't slowly creep earlier as rpm is increased, but rather moves quickly to a new value over a narrow range of rpm, is an important clue.

Originally Posted by gREgg-K
I've seen this phenomenon on my test bench as well. Sorting it out usually requires adjusting the tension of the contact breaker spring using a fixture of the type described by Lucas in their repair manuals.
I've gone through my Lucas motorcycle and car manuals but didn't see a fixture for adjusting the spring tension. Could you point me to where this information is located? Thanks.

Originally Posted by triton thrasher
If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base, you get that sudden advancing effect when rpm rises.
I didn't notice any movement of the pin when I installed the new points but I'll check this, and the fit of the points on the pin, today. Thanks for that suggestion.

Originally Posted by gREgg-K
It might be an optical illusion, but it seems to me that in the photo copied below, the contact breaker's anti-fatigue feature is assembled incorrectly:
You passed the eye test with flying colors. In my attempts to locate and eliminate this effect, and to keep the spring as far from touching the cam as possible, I assembled the spring in various ways to see if it made any difference. The photos of the correct assembly were earlier on my iPhone which meant I ran across the incorrect photos first as I worked backwards looking for photos to post. I uploaded those incorrect ones because I came across them first as I worked backwards through the iPhone album and, hey, who would spot the difference?...
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 06/03/19 5:43 pm

Originally Posted by Magnetoman
<SNIP>The move from analog to digital wasn't because digital is better, it was largely driven by competition from manufacturers offering digital 'scopes with color displays, clean-looking signals, and automatic setup of triggering at a push of a button for a lot less money. Since that satisfied the needs of the majority of customers, it killed analog. It's also why you can find a 2465B on eBay for a lot less than $14k.
<SNIP>

I agree fully with you about digital scopes. The high point of my early design engineering career was when the company gave me a new Tek 465B as my "welcoming gift". During the following 35 years, I had numerous others, but I never got (or wanted) a digital scope. I like the comfort of knowing that what I see on the screen is an analog of what is happening in the circuitry I'm examining ... not a digital interpretation, no matter how clean or pretty. I have a 2465A in my personal lab, and like your 2465B, it serves very well.

Originally Posted by Magnetoman
[/quote]I've gone through my Lucas motorcycle and car manuals but didn't see a fixture for adjusting the spring tension. Could you point me to where this information is located? Thanks.

Originally Posted by triton thrasher
If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base, you get that sudden advancing effect when rpm rises.
I didn't notice any movement of the pin when I installed the new points but I'll check this, and the fit of the points on the pin, today. Thanks for that suggestion.

A loose and/or worn pivot pin is a common problem with these contact breaker assemblies. Lucas did not to my knowledge produce a drawing of a fixture to check the spring tension, preferring instead to leave "the how" to the ingenuity of the reader of the specs they published in the magneto Workshop Instructions. I built my own fixture with the back end of a scrap K2F armature, and using a digital "fish scale" to do the measuring. I built the fixture so that one can mount and measure either clockwise or ant-clockwise contact breaker assemblies.

[/quote]
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/03/19 8:36 pm

Originally Posted by chaterlea25
A diamond coated needle file (LIdl or Aldi and probably Walmart) will file the hole in the spring to elongate it where it is clamped by the securing screw moving the curve away from the cam ring
Done. I already had a box of appropriate diamond-coated Dremel bits for drilling holes in sea shells brought home from Calif. by my granddaughters to make necklaces. As the first composite photograph shows one of them made short work of making the slot longer. The second photograph shows there's now a comfortable distance between the spring and the cam.

Originally Posted by triton thrasher
If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base,
Originally Posted by gREgg-K
A loose and/or worn pivot pin is a common problem with these contact breaker assemblies.
The pivot is quite tight in the base. The third photograph shows that the clearance of the hole in the rubbing block is 0.0015", and in the other two NOS sets of points it was 0.0020", so that doesn't seem to be the issue, either

This time I shimmed the top and bottom of the rubbing block with fiber washers and attached the spring clip to give essentially zero freedom for up/down movement on the pivot pin, but not to restrict its rotational motion. Whether it was the somewhat tighter spring due to the enlarged hole, or the shimming of the rubbing block, this time it no longer jumped to earlier opening as the rpm was increased. It did start sparking at the original (arbitrarily-set) 0-deg. along with ~2-deg. retarded at high rpm, which is much less problematic than changing to too-advanced.

I moved it back to the long-term tester to put an hour on it to make sure everything is bedded in before I'll move it back to check the timing again. Anyway, significant progress has been made.


Attached picture MagnetoTiming05.jpg
Attached picture MagnetoTiming06.jpg
Attached picture MagnetoTiming07.jpg
Posted By: gREgg-K

Re: Correct needle for 1000-series Concentrics? - 06/03/19 8:51 pm

There is something else about this contact breaker assembly that't not quite right:
[Linked Image]

Posted By: triton thrasher

Re: Correct needle for 1000-series Concentrics? - 06/03/19 8:54 pm

For how long will your zero end float last, I wonder?

Shouldn’t matter, if the spring was causing the jumping timing effect, of course.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/03/19 10:29 pm

Originally Posted by triton thrasher
For how long will your zero end float last, I wonder?
Once the face of the rubbing block is fully bedded with the cam there will be no upward or downward force so the end float shouldn't increase. And a few thou. increase shouldn't matter, anyway.

An iPhone is like a digital oscilloscope, i.e. terrible for capturing transient. I took several dozen photos before I got one that sort of shows what is now going on at high rpm. Visually most sparks are still at 0-deg. but every second or so (i.e. 30 revolutions if it is spinning at an estimated 2000 rpm) a spark happens later. Typically, the late sparks are at ~2-deg. (4-deg. engine) but this photograph happened to capture a spark at ~4-deg. (8-deg. engine). [*]

[*] after another 30 min. spinning at 2000 rpm on my long-term tester the sparks are more stable at 0-deg. with fewer excursions to 2-deg. retarded and none more than that.

If 3% of the sparks are late so the engine produces only, say, ~70% of the power on those strokes it would result in an overall loss in h.p. of 0.9%. I may just decide to suck it up and accept that loss, compounded by the h.p. loss due to having a Concentric instead of a GP.

Question for Gold Star owners to ponder: if my Competition magneto does this, how do you know yours doesn't?

Originally Posted by gREgg-K
There is something else about this contact breaker assembly that't not quite right:
What, pray tell? I've assembled and disassembled it enough times that I couldn't see a huge issue if it was staring me in the face. Which, in the photograph, it is.




Attached picture MagnetoTiming08.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/04/19 7:45 pm

Unfortunately, I'm stuck carefully reading and editing about 50 single-spaced pages of material today so, along with other obligations, time in the garage was limited.

The capacitors for the dead Battery Tender arrived yesterday so I installed one and it has now rejoined the living. While doing this I put another 15 min. of time at 2000 rpm on the magneto. It's unlikely I'll have time to install it today so there's still time for gregg-k to let me know what he sees wrong with the current points assembly.
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 06/05/19 6:17 am

Doing a bit of catch up so I am a bit further behind than normal but is there any reason wht the spring could not be encased in some heat shrink ?
In the past I have seen some points sets where the spring was insulated,
Posted By: triton thrasher

Re: Correct needle for 1000-series Concentrics? - 06/05/19 9:48 am

Originally Posted by BSA_WM20
Doing a bit of catch up so I am a bit further behind than normal but is there any reason wht the spring could not be encased in some heat shrink ?
In the past I have seen some points sets where the spring was insulated,


I’ve found them taped up before.

It would soon wear through and pressure from contact with the cam might break the spring eventually.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/05/19 4:32 pm

Originally Posted by BSA_WM20
is there any reason wht the spring could not be encased in some heat shrink ?
Originally Posted by triton thrasher
It would soon wear through
When I first installed the new points, before lengthening the slot with a diamond tool as suggested by chaterlea, I used a piece of paper between the spring and the cam to gauge the clearance as I rotated the points assembly. At the point of closest approach I had to tug on the paper to move it so the clearance was only ~0.003". That doesn't leave much room for insulation even if the spacing stays the same when rotating at 3000 rpm. Also, both the wear of the rubbing block and of the points will decrease the spacing between the spring and cam so even if the spacing is (barely) fine now, it only will get worse with time.

Once concern is the spark breakdown voltage for plane-parallel plates spaced 0.003" in air is only 600 V (possibly less in the presence of ozone, although a quick search didn't turn up any information on this), decreasing to 400 V at 0.001". This is roughly the voltage across the capacitor in the primary circuit when the points open. But, even if there were room for insulation, would it help? It's actually not an issue since the point that opens, that's attached to the spring, is always at earth potential, as is the cam.

Leaving aside abrasion, given that sparking between the spring and cam isn't possible, the remaining electrical concern is that if the spring touches the cam it would discharge whatever current is flowing in the primary at that time, leaving a reduced amount available for the spark plug. However, that's not actually an issue, either, since the places where the spring could touch the cam come at times when the points are open so no current is flowing in the primary anyway.

So, not leaving aside abrasion, abrasion is the concern.
Posted By: edunham

Re: Correct needle for 1000-series Concentrics? - 06/05/19 6:10 pm

Can the spring be attached to the inner side of the post instead of the outer?


Ed from NJ
Posted By: bsalloyd

Re: Correct needle for 1000-series Concentrics? - 06/05/19 7:32 pm

Did you ever solve the roller issue? If not try using your lathe and put a deep knurling pattern on them. Even if it doesn't work it will give you a better surface for the adhesive to adhere too.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/05/19 8:17 pm

Originally Posted by edunham
Can the spring be attached to the inner side of the post instead of the outer?
It could, but the post itself is threaded and it would be very difficult to tighten a screw installed from the inside (and it would be a tight fit for a nut), and it also would add quite a bit of tension to the spring. It's quite possible that the ~0.003" clearance with the new points would have turned out to be fine even in the long run, but it was just too close for my comfort. Lengthening the slot in the spring was easy and it gave enough additional extra clearance to make me happy.

Originally Posted by bsalloyd
Did you ever solve the roller issue?
It turned out to be a "breather issue" rather than a "roller issue." Before I discovered the problem the replacement abrasive paper already had been torn up but even then the rollers have had no problem at all starting the 10:1 engine multiple times. DocZ offers a set of "forever" rollers with slots and powder paint embedded with grit, and I'll probably buy a set once my current jetting experiments are done. They're sold using the current rollers as exchange and I don't want to be without my DocZ until I foresee a few weeks of down time.

You might remember that my friend's shop burned last month. He was able to salvage some things that he moved to space he rented a few weeks later. Today he asked for help rearranging the ten or so bikes (including my A65) that more or less made it through the fire. It's pretty sad. The fiberglass tank on a round-case Ducati looks like a chia pet. The lower yoke on a (formerly) very pretty small Ducati was completely melted into a puddle. He said he had taken a Moto Guzzi home immediately after the fire, before he had the new rented space, but when he looked at it on the trailer the next morning he realized there wasn't a single salvageable piece on it so he hauled it back to the shop to be disposed of.

The Gold Star connection to this is today he gave me a header pipe and twitter silencer he rescued from the rubble. Along with another Innovate LM-1 I picked up for very little because it was mis-listed, I'll now be able to get the jetting sorted out on an ultra-rare twin-port Gold Star should one come my way.


Attached picture DocZ_rollersJune2019.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/06/19 2:52 am

It was an interesting day in the lab... er, I mean, garage.

I wrote a very long post immediately after coming in from the garage but decided I need to think about it a bit more so I'm temporarily deleting it. Stay tuned.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/06/19 3:25 am

Mot being savvy with the operation of the oscilloscope and the data one can produce, one wonders what the makers of magnetos used to determine how their products worked, or didn't? And could they have improved the basic magneto if they did have the modern data? I suppose that question is answered by the development of modern CDI ignitions (by subsequent generations of ignition engineers) ...the first of which had a very short spark duration and weren't that successful.

One also wonders if modern magneto rebuilders go to these lengths to identify problems or check correct functioning? I'm sure some have the knowledge and capability...though surely not all.

KW
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/06/19 5:19 pm

Originally Posted by Kerry W
Mot being savvy with the operation of the oscilloscope and the data one can produce, one wonders what the makers of magnetos used to determine how their products worked, or didn't?
I decided I wanted to make another measurement to add to yesterday's lengthy, temporarily-deleted, post before reposting it. Meanwhile, the attached figure from the 1933 edition of 'Automobile Electrical Equipment' by Young and Griffiths addresses your question. This book started out c1920 as 'Magnetos', with the renamed book adding chapters around the core of the original.

The figure shows two spark points on what is essentially the same apparatus as my modified distributor tester. The text explains that they observe a bright white flash between the two spark points when the spinning apparatus reaches position A, with a weaker flame continuing for several degrees after that as the apparatus spins further. By knowing the rotational speed and the fact that the bright flash doesn't appear to be "smeared" out they estimated that it must last only ~1 microsecond. This was the instrumentation available to them in 1933 to try to understand how sparks are generated. Today, a 50 MHz high voltage probe connected to a 400 MHz oscilloscope lets me directly "see" the details of the spark at a time scale 50x faster than they could even estimate.

Going even further, I have two high frequency current probes as well so, along with the 4-channel oscilloscope, I can simultaneously watch what is happening at each instant in time to the primary and secondary currents and voltages. This is easier done with a rotating magnet magneto since it doesn't require making electrical contact with a spinning points plate (making that contact isn't too difficult, but doing it without a lot of electrical noise is).

Originally Posted by Kerry W
if modern magneto rebuilders go to these lengths to identify problems or check correct functioning? I'm sure some have the knowledge and capability...though surely not all.
If I were rebuilding magnetos for a living I would have long ago gone bankrupt. I spent hours in the garage yesterday spinning the magneto and taking data, only to think of an additional experiment to run today. Add to that the time I spent changing the points, lapping the taper, and magnetizing it and I've easily been working with it for the equivalent of two full eight-hour days and I'm still not done with it.

I've written before that a bad experience with a magneto restorer 25 years ago set me off on the quest to understand these devices at the most fundamental level possible. As a result of that experience I've assembled what certainly must be by far the most heavily instrumented "magneto research facility" in existence. No rebuilder "needs" instruments to measure resistances from 10 µΩ to 1000 TΩ (1 thousand million MΩ), 6½-digit DVM that can detect the difference between the resistance of the 5000 Ω secondary coil alone and the 5000.5 Ω resistance of it plus the primary coil, 200 Watt 1 MHz pulse generator for stress-testing capacitors, etc. However, having these instruments lets me check functioning and identify subtle problems better than if I didn't have them.

If I regularly rebuilt magnetos as a business, rather than only one every year or so, each one certainly would go faster. However, although magnetos certainly can function well without being tested at the level I test them (or fail even then if a screw isn't Locktited), it's difficult to see how someone could go to the lengths I do to understand and characterize these devices and do so at a profit.

A "living wage" in most of the U.S. is $18/hr. for a family of 2 adults with one working. Coincidentally or not, this is the average hourly rate paid to automotive technicians in my town, even though garages bill at the rate of $80-100/hr. to cover that plus expenses and profit. Someone who rebuilt magnetos at the rate of 2 per week would have to charge $375 ea., plus parts, to reach that wage if it were their sole source of income. The median household income in the U.S. is $61.4k ($235 per working day). If they upped their production to one/day they could drop their price to $235 ea. to reach that somewhat higher standard of living.


Attached picture MagnetoTiming14.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/06/19 7:33 pm

These days, if I knew it was being done to the standards above, I'd pay the price...
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/07/19 12:04 am

If you don't like technical topics, let alone long technical posts, now would be a good time to avert your eyes.

It turns out in the absence of a working tach I had significantly underestimated the rpm of the modified distributor tester. I'll come back to that in a moment, but having seen sparks that started coming too early at high rpm I put the magneto back on the long-term tester for another hour. I have the tester on a wooden workbench, and I didn't want to leave it running there while I was away, so that gave me time to make some other measurements.

In an earlier post you can see the spark but you can also see a magenta arc extending 5-7 degrees beyond the spark at whatever rpm was used at that time. So, why the magenta arc? I have a Tektronix high frequency, high voltage probe from the 1970s that is good for measuring 40 kV signals at up to 50 MHz (i.e. time constant 20 nsec). For voltages that high it has to be filled with Freon 114, manufacture of which was banned nearly 25 years ago. However, I have one pint of the precious substance that I'm saving for a rainy day (as if working with 40 kV on rainy days is a good idea...). Luckily, though, the probe is good for 13 kV without Freon. So, I connected it to analyze the signal while the magneto was running anyway.

The two traces of the first photograph show several sparks as seen on the displays of an analog (top) and digital (bottom) oscilloscope. The voltage probe is 1000:1 so each 1 V signal on the oscilloscopes corresponds to 1 kV. It can be seen that the signal repeats after 29 ms which indicates the magneto is spinning at 2069 rpm (1 rev./ 29 ms x 60 sec./min. = 2069 rpm). Starting in the middle of the top trace, what it shows is the voltage at the end of the spark plug wire starts out at 0 V with respect to the housing, abruptly goes negative by some number of kV (to be determined below), recovers somewhat to a skewed plateau value of ~1 kV for ~4 ms, after which it returns to near O V for ~8 ms, then goes nearly 3 kV positive, after which it returns to near 0V until the cycle repeats.

My Tektronix 2465B has the valuable feature of a second time base that I can trigger an arbitrary delay after the main trigger. Although I can display both the main and expanded signals at the same time, it's easier to photograph when I've displaced the main one off the screen and increased the intensity, as I've done for the bottom half of the second photograph. The region where the potential abruptly goes negative is expanded by 50x in the bottom trace, where the horizontal scale is now 100 µs. As can be seen, it takes the potential ~20 µs to get to -3 kV, after which it jumps back to ~-600 V in a time that's too short to be determined from this trace. That is, it takes ~20 µs after the points open for the voltage to reach a large enough value to cause electrical breakdown in the air, at which point the voltage drops "instantly" (i.e. a very short time to be determined below). The ghost traces show that the timing of these features jumps around by ~200 µs which, at the rotational speed of 2079 rpm, corresponds to an angle of 1.2 degrees. However, it's not quite that bad since this jitter depends on where the oscilloscope trigger is set. The modified distributor tester shows the jigger is less than 1 degree (2 degree engine).

Note that the voltage when the spark takes place is negative. This means electrons will be "pushed" from the relatively sharp central electrode of the spark plug and travel to the relatively flat earth electrode. If the magneto were magnetized in the opposite way electrons would be attracted from the earth electrode. Since it requires less voltage to eject electrons from a sharp electrode than from a flat one, this magneto is properly magnetized to initiate an arc with the greatest ease, which is just what you want for starting a 500 cc single. With a twin magneto this effect means one side works a bit better than the other, which only is important when magnetizing a V-twin magneto.

Going 500x shorter in time, to 200 ns/division, the third photograph shows what happens at the instant the voltage reaches the breakdown voltage of air. Basically, the time scale is close enough to the claimed 20 ns response time of the high voltage probe that, without calibrating the probe response with at least a 100 MHz square wave, all it's safe to say is that within no more than 40 ns after the spark was initiated the voltage has dropped to a new plateau value followed by damped ringing for ~800 ns.

As my previous post mentioned, with 1933 technology they estimated the main spark took place in no longer time than 1 µs. The oscilloscope trace shows it takes place in no more than 40 ns, i.e. at least 25x faster than that 1933 estimate.

At 3500 rpm, which is the maximum rotation rate the magneto needs to reach the 7000 rpm engine redline, it makes 58.3 revolutions/sec. The oscilloscope traces show that the lingering arc lasts for another 4 ms after the main arc. If sufficient current remained in that lingering arc for the discharge to remain visible for 4 ms that would be 58.3 rev/sec. x 4 msec. x 360-deg/rev. = 84 degrees. In fact, the visible arc in the fourth photograph lasts only ~10 deg. so by 10/84 x 4 ms = 0.5 ms so that's how long it takes for enough energy to be dissipated that the arc is no longer visible.

The fourth photograph shows the behavior observed in 1933, with a sharp bright spot followed by a lingering arc. Again, the rotation is CW in the photograph.

Because of the limitations of the iPhone camera I had to take ~20 photographs before I captured the dot of light at 351-deg. in the fourth photograph, i.e. well before the points should have started opening. The main spark actually remained at 0-deg. but in doing all of this, including dropping my iPhone when my elbow touched a piece of the tester and received a 2.8 kV jolt, I didn't notice the scale had moved.

The first signs of these dots of light appearing before they should have was at 3100 rpm (6200 rpm engine), with the dots becoming more frequent by 3280 rpm (6560 engine). The fourth photograph was taken at 3340 rpm (6680 engine). Although that dot of light is a spark of some sort, it doesn't have the characteristics of a "real" spark, i.e. it lacks a long tail due to energy from the coil being dissipated. At this point I don't know what those dots of light are. However, since it takes a few mJ of energy to initiate ignition, and since a magneto isn't designed to produce much more than that minimum, and since such a "real" spark results in a long arc trail, it's unlikely those dots of light have enough energy to cause premature ignition.

My long-term tester is much more rigid than my modified distributor tester so I ordered a larger pulley to increase the speed from the present 2000 rpm to a little less than 3500 rpm. That way I'll be able to see the electrical signature of those parasitic dots of light with the oscilloscope. However, I'm inclined to install the magneto tomorrow and save additional measurements for some undetermined time in the future.

Turning to a question raised by George Kaplan, I had time on my hands while the magneto was logging hours yesterday so made other measurements as well. The first photograph shows the sort of square-wave-like behavior around the time of the spark. The bottom of the second photograph is a 50x expanded portion of the upper traced, with the "ghost" lines indicating that part of the waveform fluctuated considerably. What this analog oscilloscope lets me do is simultaneously watch, in real time, the overall behavior while also seeing these fluctuations to observe the actual behavior of the spark.

The top of the fifth photograph shows the same region as in bottom of the second, except on a digital oscilloscope. Clearly, nothing much can be learned from this trace. However, it's not an entirely fair comparison since there are other ways to use the digital 'scope to do better than this. Still, since I own both types of oscilloscopes I have my choice, but I turn to analog for a situation like this.

Two things a digital 'scope can do that often are quite useful are shown in the first and fifth photographs. The bottom trace of the first shows many sparks because the time base is set to a long 10 ms/division. If an analog oscilloscope had a setting much longer than this the initial pulses would have faded from the screen long before the final pulses were registered, whereas a digital oscilloscope -- more accurately known as a digital storage oscilloscope (DSO) -- displays the trace for the full length of the sweep (or, forever, if the 'save' button is pushed). The lower trace is a Fast Fourier Transform (FFT) of the upper trace, which transforms data from the time domain to the frequency domain. The peak heights and frequency spacing between peaks can provide very useful diagnostic information in many circumstances (although not in this case).

I haven't even scratched the surface on the strengths and weaknesses of the two types of oscilloscopes (nor sub-categories, like analog storage oscilloscopes). But, it's horses for courses. For most automotive purposes I find an analog 'scope better, but for some things only digital will do.



Attached picture MagnetoTiming15.jpg
Attached picture MagnetoTiming16.jpg
Attached picture MagnetoTiming17.jpg
Attached picture MagnetoTiming10.jpg
Attached picture MagnetoTiming18.jpg
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 06/07/19 7:44 am

Hello MM, thanks for taking the time to do this work and write about it. I read it twice and found it both interesting and informative (to a point due to my level of knowledge and experience with electrical circuits and electronics)

I have a simple question. Taking this data along with everything else that you have learnt about magneto's, what does this tell us in practical terms about:

a) Your magneto and the issues that you were having?

and

b) Magneto's in general and what this tells us about what we should or shouldn't do with them when maintaining/rebuilding or just using them?

John
Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 06/07/19 1:11 pm



Good morning, folks,

Many years ago, when MM and I were at our second or third Irish National Rally in County Cork (the 'Munster), MM bravely (or rashly) volunteered to give a talk about magnetos to the assembled throng.

As a pilot of light airplanes, I had long been used to testing magnetos during engine run-ups (there are two mags, for redundancy, in a typical light airplane). And I knew that magnetos in aircraft rarely, if ever, fail. Why? Because they are serviced regularly by mechanics who understand how they work, and what is needed to keep them in perfect condition. MM used this example in the preamble to his talk, implying that if magnetos are so reliable, why do they so regularly 'pack up', in old motorcycles.

The talk was, as you might expect, illuminating, and MM went into detail about coils, primary and secondary, the relationship between magnetism and electricity (Einstein would have been proud), and, most critically, the shelf life of capacitors. One guy in the audience took all this in so comprehensively that he became (and remains) a skilled magneto restorer. Many were enlightened, others amused. But several were downright dismissive. One, a chap who wrote a technical column in a British classic bike magazine, loudly denounced the whole talk as a 'load of bollox'.

And to answer George's question, this information has plenty of practical things to say about how we use our magnetos, day-to-day. But I will leave that to MM to elucidate.

TGIF,

Ultan

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/07/19 3:38 pm

Originally Posted by George Kaplan
what does this tell us in practical terms about:
a) Your magneto and the issues that you were having?
and
b) Magneto's in general and what this tells us about what we should or shouldn't do with them when maintaining/rebuilding or just using them?
Keep in mind the basic purpose of any of my posts is simply to tell you what I did. No one said I actually had to explain anything...

You can blame some of the length of my previous post on Kerry W, who had wondered how engineers studied magnetos in the old days. I answered that with Fig. 141 from a 1933 book, but that then caused me to crank up the time base of my oscilloscope to show the answer that a modern instrument gives. Some people (me, for one) enjoy learning that a magneto spark has two components, one that's over in no more than ~40 ns and the other that lingers for several ms (although it remains visible to the eye for only ~0.5 ms). However, it's hard to point to how those specific numbers would affect rebuilding a magneto, other than deviations from them means there's something wrong.

You're to blame for some of the length, as well, since otherwise I wouldn't have digressed to discussing some of the strengths and weaknesses of digital vs. analog oscilloscopes. But, it's hard to point to how knowing those differences would affect rebuilding a magneto.

Returning to your questions, my magneto had worked fine for several hundred miles, with the exception of the pinion slipping on the taper. However, at that point something changed and a misfire developed below ~3000 rpm that went away above that speed. That caused me to remove the magneto and start these recent tests to determine the cause of that misfire and to eliminate it. So, one of the practical things learned from these tests is how to modify the spring to make sure it can't touch the cam. Another practical outcome was that testing the magneto after first installing those points found rogue early sparks above 6000 rpm (engine) that could have had serious consequences. Knowing that properly installed points can result in a potentially engine-destroying problem counts as practical information that came from these tests. Also, it counts that finding that shimming the pivot to give zero end float eliminated that problem.

As NYBSAGUY pointed out, I give hour-long lectures on magnetos with over 60 images, including specific details on diagnosing problems and repairing them. That's way more information than would fit in even a dozen lengthy posts. Also, the information in those lectures is organized in a logical sequence by content, rather than sequentially (and incompletely) by time as it is here.

Reminder: an extensively documented rebuild of a magneto can be found here can be found here where much more information about the practical aspects of rebuilding a magneto can be found than in my previous post in the current thread.

Originally Posted by NYBSAGUY
One, a chap who wrote a technical column in a British classic bike magazine, loudly denounced the whole talk as a 'load of bollox'.
But, to be fair, he had reason to be grumpy. You'll remember that at the lunch stop that day I had fixed a flat for Mike Jackson (of Norton-Villiers and Andover Norton fame). Prior to my magneto lecture that evening grumpy magazine writer was pontificating to a group at his dinner table that modern tubes were made of a material that didn't allow them to be patched. Mike happened to be nearby and corrected him, saying the patch I had made at lunch had lasted the rest of the day (and the rest of the rally, for that matter). It turned out that grumpy writer had patched Mike's tube twice that morning and both had failed in a matter of minutes, resulting in the bike being hauled to the lunch stop in one of the breakdown vans.

Another unhappy listener insisted during the Q&A after my lecture that people shouldn't attempt to repair old magnetos and instead should replace them with reliable modern ones. I learned later that evening that he was the founder of the then-new BT-H company.


Attached picture MJMatchless.jpg
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 06/07/19 4:25 pm

MM & NYBSAGUY, thanks very much for your replies.

Originally Posted by Magnetoman
You're to blame for some of the length,


Blame happily accepted. Without the word "why" we would still be living in caves. Everyone should try to have an inquiring mind and be happy to learn new things (I believe I am preaching to the converted on this point). I am very appreciative of the posts that you make on here and I have read your main magneto post at least twice and referred to certain parts of it more times than that.

So it now seems that you have a magneto that you are happy with so I assume that your Gold Star will be ready for battle soon?

John


Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/07/19 4:45 pm

Originally Posted by George Kaplan
I assume that your Gold Star will be ready for battle soon?
The morning coffee has finally started to kick in so I'm about to go to the garage to install the magneto on the bike. By the time I get that done, run an errand, and the breakdown truck driver (AKA wife) returns home it will have hit the first 100 oF high of the season so I might postpone the first test ride (and jetting run) until the relative cool of tomorrow morning.
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 06/07/19 7:59 pm

Jetting runs at 100°F builds character........


laughing
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/08/19 12:26 am

Originally Posted by Rich B
Jetting runs at 100°F builds character........
Thanks for that observation, but the shakedown runs I made on my Ariel during a record-breaking heat spell last July built enough character to last me the rest of my life.

The Gold Star is back together, timed, and ready for tomorrow. I started it... well, my DocZ started it, and I made an uneventful lap of the driveway. So far, so good, but fingers crossed that all goes well tomorrow.

Before installing the magneto I ran it on the modified distributor tester and took photos at a grazing angle to give a more 3D feel. Again, it required a number of photos at 3200 rpm (6400 rpm engine) before I caught an early spark. As can be seen the main spark happens at 0-deg. (or ~1/2-deg. before that) and the wayward spark came 5-deg. before that. Also, the long tail of the main spark can be seen to be visible for 12-deg. while the early spark has no such tail, which means less energy was deposited by that spark.

The second photo shows how I have my crankshaft marked to identify TDC. This isn't necessary, but certainly makes timing the magneto a lot easier. I don't have to mess around peeking in the spark plug hole trying to see the valves moving as I bump the rear wheel.

The third photograph shows a genuine Lucas magneto cam advance fitting on the bottom and an aftermarket one on the top. The genuine article has an O-ring and, more important, is a little bit longer. The aftermarket one is barely long enough to insert the ferrule on the cable into it.



Attached picture MagnetoTiming19.jpg
Attached picture TDC.jpg
Attached picture MagnetoCamAdvanceFitting.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/08/19 11:39 pm

The goal of all my work flow testing, magneto measuring, carburetor rebuilding, and air/fuel monitoring over the past several months was to see if I could jet a 1036 Concentric to work on a Gold Star without changing the spray tube or drilling the compensating air passage. That is, I wanted to determine if only the simplest swapping of a few screw-in components would make it functional. Today all that work seems to have paid off.

First, some background. The "stoichiometric" A/F ratio for gasoline is 14.7:1. It varies from this depending on the ethanol content so λ is a better parameter to use (but, I prefer AFR so that's what I'll continue using). Maximum power from most 4-stroke engines will occur for A/F ratios in the range 12-13, although for maximum fuel economy a ratio closer to 14.7:1 would be needed. If it gets much richer than 10:1 the mixture can fail to ignite regularly, i.e. the engine will start missing, and if it is much leaner than 14.7:1 the engine can overheat and be prone to damaging pre-ignition.

I made A/F measurements under two sets of conditions, "static" and "transient." I made the former by holding the throttle in a fixed position for ~5 sec. before changing the throttle to a different position. For less than ~1/3 throttle these were made on relatively level ground as well as when going uphill and downhill. Higher throttle settings only were made going uphill to keep the speed within reason given the conditions.

"Transient" measurements were made by snapping the throttle open. I use a 1.55 V battery in my throttle position sensor so the first graph shows a 15-sec. section of the data where I was in 2nd gear at ~1/3 throttle (the red curve), then snapped the throttle closed and back open, shifting successively into 3rd and 4th where I finally gave it full throttle. The magenta A/F curve shows brief lean pulses occurred roughly 1/2-sec. after each of these throttle movements, but none are excessive and I felt no hesitation from the engine. In fact, I couldn't be happier with how the engine felt throughout this entire run today.

As can be seen from the first graph, even in regions where I kept the throttle constant the A/F curves fluctuate by ~+/-0.5 around a mean value. Added to this is the mean value at a given throttle setting at different times during the run (i.e. possibly under different conditions of, say, uphill one time and downhill another) could vary by nearly that much as well. As a result, I've drawn a band around a central line in the second graph to more realistically represent today's measurements.

A few comments about the second graph: The curve starts at an AFR of 12.2 at idle. I set the idle by adjusting the mixture screw to give the maximum rpm and this was the AFR that resulted. As can be seen, below ~1/8 throttle the mixture is richer than it needs to be. Comparing this region with the measurements I made with a #3.5 cutaway I judge that a #4.25 would be slightly better since it would raise the AFR in the valley at ~0.05 throttle. However, I don't anticipate spending much time riding with the throttle barely off idle so the fuel saved by making this change doesn't seem worth the effort.

For throttle settings between 0.2 and 0.5 the mixture is slightly leaner than the "optimum" 12-13 for maximum power. Raising the needle another notch isn't an option because that would make it much too rich in that region. However, there are two reasons I don't think this region is an issue. First, the 12-13 "rule" is just a guideline, and only time spent on a dyno would determine if more h.p. could be extracted with slightly richer mixtures. Second, most time on a machine spent cruising at mid-throttle so having a slightly leaner, but still rich, mixture will save a bit of fuel without costing any actual performance.

Before disconnecting the Innovate setup, re-installing the unmodified pipe, and declaring this episode 'done' I'll make at least one more jetting run to fill in a few additional data points between half and full throttle. However, I had a close call with a sheriff's car today. I had just come down a hill and made a U-turn onto a side street and was waiting for traffic heading up the hill to get far enough along that I wouldn't catch up with them. Had I taken off 5 sec. earlier I would have been going well over 60 mph (with a 35 mph speed limit) when the sheriff's car came around the curve at the top of the hill.

In conclusion: the 1036 Concentric jetting listed on the second graph is perfect-ish for my Gold Star.


Attached picture AFR_8June19_01.jpg
Posted By: RPM

Re: Correct needle for 1000-series Concentrics? - 06/09/19 2:33 pm

The last and only Gold Star I have worked on with a 1036 carb it was jetted

4 stoke jet holder
230 main
needle in middle
25 pilot
106 needle jet
4 stroke spray tube
3 1/2 slide

How would the 2 stroke spray tube with leaner slide compare to the 4 stroke spray tube with slightly richer slide? You have all the stuff hooked up, slap a 4 stroke spray tube and slide in and go for one more ride.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/09/19 3:50 pm

Originally Posted by RPM
How would the 2 stroke spray tube with leaner slide compare to the 4 stroke spray tube with slightly richer slide? You have all the stuff hooked up, slap a 4 stroke spray tube and slide in and go for one more ride.
Unfortunately, I turned one of my slides into a #4 (after initially making it a #3.5) so right now only have one ea. #2, #3, and #4 slides. So, I can't do the measurement needed for a direct comparison with your result. However, I can speculate based on the data I do have.

Actual measurements always are best but, when they're not possible, estimates based on related data can be quite useful. The flow bench results I posted in April showed that at full throttle the 2-stroke spray tube (with unmodified air compensation passage) increases the pressure difference ("vacuum signal") by 21%. That says, all other things being equal (such as the air filter you did or didn't use, which is a big factor), your 230 main would imply mine should have been a 190 to give the same mixture as yours. My 220 gives a rich-ish 12:1 at full throttle so if I swapped it for a 190 the AFR would change to 230/190x12= 14.5:1. A bike should run without apparent problem with that leaner mixture so your main jet and mine are consistent.

The smaller "vacuum signal" from your spray tube also would draw less fuel into the air stream than mine at lower rpm and hence yours would require a richer slide than mine. Again, your slide and mine are consistent.

The difference in "vacuum signal" at 1/4 throttle, where my AFR curve has a broad peak, is 15%. Despite this difference, which is smaller than that at full throttle, your needle is on the same the middle slot as mine. However, the AFR in this region depends on both the cutaway and the needle position so I can't say whether or not this is an inconsistency.

Given the uncertainty in your configuration (i.e. the air filter), and the fairly broad range in AFR where the effect on performance is subtle (i.e. between 11:1 and 14:1), your jetting and mine are consistent. Although my jetting has the advantage that it's backed by actual AFR data, it's worth repeating that they're the best results possible with an unmodified air compensation passage and 2-stroke spray tube, not necessarily the absolutely best results possible (still, my bike runs great with this jetting). I'll end with the phase included in the conclusions of just about every scientific paper: further experiments are needed.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/10/19 12:58 am

I decided not to spare you from the dark underbelly of jetting a Concentric. Rather than draw a smooth curve the attached graph shows two day's worth of data in all its glory. By the way, those data don't plot themselves. It takes the better part of 2 hours after each run to find the one or two dozen time intervals worth examination, copy them to Photoshop, format, print, and then mark the AFRs and measure the corresponding relative throttle openings from the 0-1.55V signal from the throttle position sensor.

The first thing to note is I changed the main jet from one marked '220' that I used yesterday to one marked '200' today. This should have leaned yesterday's ~12:3:1 at full throttle to 13.5:1. Instead, the mixture became richer by the equivalent of having changed a 220 to a 225 rather than a 200. I've mentioned several times over the years that I measured a number of '500' Amal main jets on my flow bench and found 25% of them to be as much as 3½ sizes too large or too small. The other 75% weren't perfect, having a spread of almost +/-1 jet size. Anyway, as these two jetting runs show, the '200' in it now is somewhat richer than the '220' that was in it yesterday.

I don't know if the '220' is smaller than its marked size, or the '200' is larger, but they're close enough that it makes sense to plot both sets of data on the same graph. Unfortunately, to measure the relative flow of the two jets would require me to dismantle the carburetor fixture from the flow bench, which I'm not inclined to do because I have more measurements I want to make. After plotting all the data I examined the outliers to see if I had made any mistakes, or if I had extracted any of them from graphs where I hadn't allowed the mixture to stabilize for ~4 sec. This removed three data points, but the three x's between 0.4 and 0.5 are real.

The scatter of the data points isn't due to experimental uncertainty in reading the values from the graphs, it is real. The same throttle setting under different conditions (e.g. accelerating on level road vs. climbing a hill) gives somewhat different AFR readings. Also, after yesterday's run the AFR at idle was 12.2. Today it was 11.5 even though I hadn't touched the mixture screw in the meantime.

Trying to find information on the "perfect" air/fuel ratio for gasoline, let alone E10 or E15, quickly takes one down a rabbit hole. If information is correct that 13.5:1 is the ideal ratio for maximum power then my present ~12:1 robs me of ~2%. However, if 12.5:1 is the correct ratio, my current jetting essentially robs me of nothing other than the price of having to refuel 4% more frequently if I ride all the time at full throttle. On the other hand, if much of my time is spent between 1/8 and 1/4 throttle my current jetting gives me better economy at the cost of only ~1% of the power in that range.

Just as with yesterday's '220', the performance with today's '200' felt perfect. The current configuration of the bike makes it a lot of fun to ride. At this point I'm, ahem, leaning toward calling it rich enough and removing the A/F sensor and associated apparatus. If it weren't the onset of summer I would be strongly inclined to inflict these measurements on the Catalina next. That might have to wait until Fall.


Attached picture AFR_9June19_04.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/10/19 1:08 pm

Looking at the scatter of the data points, one things clear to me (in simplistic terms)...it's economical in the area of throttle openings likely to be used at sensible traffic speeds (where economy is a bonus) and will make good power at the throttle openings where power is required - big handfuls for going fast, accelerating and up hills..nice.

Looks like you have it nailed, the proof being that it's fun to ride..which I take to men that it responds readily, carburets cleanly and performs well...which is both satisfying to the tuner and rider alike.

Good effort.

KW

PS ..ad you solved problems with the mag, starter and battery charger/s that you didn't even know you had!
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/10/19 4:58 pm

Originally Posted by Kerry W
PS ..ad you solved problems with the mag, starter and battery charger/s that you didn't even know you had!
Yeh, sort of like setting out to simply install a new spark plug and ending up rebuilding the engine, gearbox, and both brakes before the plug is finally in place...

Luckily, I enjoy this sort of thing, but progress can be slow since I can't help digressing into making flow bench measurements, capturing 400 MHz oscilloscope traces, machining tachometer-drive timing checking tools, etc.

The only known problem that remains with this Gold Star is that its 10:1 piston isn't happy with 92 octane fuel and 100 oF temperatures. Despite using a name-brand octane booster I still heard a worrisome rattle a few times during these jetting runs so I have on order a super-expensive booster that will give me 100 octane at the equivalent cost of ~$8/gallon (I know, I know, Europeans won't be sympathetic when reading that number). "Racing fuel" is available at a few hot rod shops in town at approximately the same price, but the advantage of an additive is 8 oz. will turn a 2-gal. tank of 92 into 100 octane. Eight oz. is a small enough quantity to easily carry with me and will allow a range of ~200 miles away from the rest of the bottle back at base.

I don't know what piston is in my Catalina, but the only time I heard it rattle was when I turned onto an uphill street going too slow in a gear that was too high. Quickly grabbing the magneto lever and downshifting dealt with that. The 'Competition' isn't as easy-going.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/10/19 6:10 pm

10:1 is certainly 'adventurous' on 92...I'd have expected not more than 9:1 and probably more like 8.5...

I know of a guy who is in the process of quantifying how much or little effect that drop in compression might have on perceived performance...

KW
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/10/19 6:31 pm

Originally Posted by Kerry W
10:1 is certainly 'adventurous' on 92...I'd have expected not more than 9:1 and probably more like 8.5...
'Competition' Gold Stars came with 10:1 pistons and when I rebuilt the engine 25 years ago just about every station carried high octane fuel so it wasn't a problem. Now it is.

If it worked as advertised the Lucas octane booster I used increased the octane to 95. Since the engine still knocks at 95 it needs more octane than that. Eight oz. of the stuff that's on its way to me now will increase it to 100 and, if that's not enough, 12 oz. is supposed to be good for 104. If it still knocks with 104 then rebuilding the engine as a side valve may be my only remaining option...
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 06/10/19 7:31 pm

Originally Posted by Kerry W
10:1 is certainly 'adventurous' on 92...I'd have expected not more than 9:1 and probably more like 8.5...
KW


My XR400 has a standard 10:1 compression ratio and my friends KTM 640 has a higher ratio (I forget if its 11:1 or 12:1).

In the UK, standard pump fuel is 95 or "Super" is 97/98.

Neither of us have had problems using standard pump fuel so why should a GS need a higher octane rating.

Now I know that there is a 50 year age difference but surely its not just compression causing the knocking? I am not asking a question per se but just remarking on how two different bikes with similar CR's seem to react differently on pump fuel.

John
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/10/19 7:48 pm

Originally Posted by George Kaplan
why should a GS need a higher octane rating.
A half-century worth of work into combustion chamber design is what allows modern bikes to have those high CRs.
Posted By: gavin eisler

Re: Correct needle for 1000-series Concentrics? - 06/10/19 11:21 pm

A great read MM, most interesting . You got me googlin for Air Fuel ratio meters. The magneto spring eh, who would have thought, great catch, and the pivot shim . Snap that stuff up at 8$ a gallon, here 98 is £1.40 a litre, 91 is £1.30, my bike cost 10 pence a mile to run fuel alone.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/11/19 12:18 am

Originally Posted by gavin eisler
A great read MM, most interesting .
Thanks very much for the comment. The technical content often isn't typical Britbike fare so it's nice to hear it's appreciated.

Originally Posted by gavin eisler
The magneto spring ... and the pivot shim .
A larger pulley arrived today and from now on I'll test my magnetos at lower speed and then at the equivalent of 6200 rpm engine.

Originally Posted by gavin eisler
here 98 is £1.40 a litre, 91 is £1.30, my bike cost 10 pence a mile to run fuel alone.
I knew Europeans wouldn't have much sympathy for $8/gallon. Today's price of 92, the highest at the pump where I live, is $3.07/gal = £0.64/l. The cheap stuff, 87, goes for $2.63/gal =£0.55/l. The difference is "only" a factor of ~2, but gasoline to ride a motorcycle in the U.S. feels pretty much like an incidental expense, but every time I replace the nozzle after filling the tank in Ireland a serious number is staring at me on the pump.

I mentioned a few days ago that I managed to grab a second Innovate LM-1 that had been mis-listed on eBay. I decided that given the usefulness of the device, along with my modified Gold Star pipe, it would be good to have a backup. However, I realized I hadn't fully tested it so today I hooked it up, connected the cables to the DocZ, but then was overcome with the urge to try to start the bike the old fashioned way. I'm happy to report it only took a couple of kicks and I'm still able to walk afterwards. I made three laps of the driveway and downloaded the data. The new LM-1 works fine.

Interestingly, the new LM-1 is a different color than my original one and has a much higher serial number so I must have been a fairly early adopter. Assuming they started their numbering with 1000, my original one would have been one of the first 2800, with the second one some 15,000 later. On the other hand, did they really sell at least ~18,000 of these specialized units in the less than a decade before it was replaced by the LM-2?

Posted By: Shane in Oz

Re: Correct needle for 1000-series Concentrics? - 06/11/19 2:06 am

Originally Posted by Magnetoman
If it worked as advertised the Lucas octane booster I used increased the octane to 95. Since the engine still knocks at 95 it needs more octane than that. Eight oz. of the stuff that's on its way to me now will increase it to 100 and, if that's not enough, 12 oz. is supposed to be good for 104. If it still knocks with 104 then rebuilding the engine as a side valve may be my only remaining option...
FWIW, 1960s Land Rover workshop manuals recommended retarding the ignition timing for lower octane fuels, and from memory there was a table of ignition advance vs octane rating. Some of the places where those things were used had very low octane fuels, too.
I think I have a manual in the shed, which I can dig out next weekend if somebody hasn't provided useful information beforehand
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/11/19 2:49 am

Originally Posted by Shane in Oz
I think I have a manual in the shed, which I can dig out next weekend
That could be quite interesting. After I read your post searched for such information online but couldn't find anything.
Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 06/11/19 7:17 am

Originally Posted by Magnetoman
I knew Europeans wouldn't have much sympathy for $8/gallon. Today's price of 92, the highest at the pump where I live, is $3.07/gal = £0.64/l. The cheap stuff, 87, goes for $2.63/gal =£0.55/l. The difference is "only" a factor of ~2, but gasoline to ride a motorcycle in the U.S. feels pretty much like an incidental expense, but every time I replace the nozzle after filling the tank in Ireland a serious number is staring at me on the pump.


Looking at your numbers it would seem that $8/gallon is about £1.67/litre which is about 28% more than the UK so you do have "some" sympathy.

Further to my earlier comments I didn't realise (even though I have driven in the USA many times) that standard gas was only 87 and the better stuff only 92. Compared to the UK where it is 95 & 98 respectively.

John
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/11/19 3:39 pm

Originally Posted by George Kaplan
Further to my earlier comments I didn't realise (even though I have driven in the USA many times) that standard gas was only 87 and the better stuff only 92. Compared to the UK where it is 95 & 98 respectively.
Don't start feeling superior for having higher octane number than us. Like 'The Three Bears' there are three common rating systems for the anti-knock properties of gasoline: Motor, which gives a somewhat low number, Research, which gives a somewhat high number, and (R+M)/2 that gives a number that's in the middle (I'll call that number 'G' for Goldilocks). England uses R while the U.S. uses 'G'.

As far as I can tell the U.S. used R to rate octane at the pump until the early '70s, then switched to the present 'G' system. So our old 98 'premium' of the 1960s was roughly the same as your current 98 and probably is equivalent to something like 'G'= 93. Although slightly higher octane is available in some places in the U.S., California, Nevada and Arizona all get the same blends, which gives me a maximum of 'G'=92. In the 1960s we also had R=102 'super-premium' which my 10:1 Gold Star likely would be happy with. Assuming the octane booster I used increased my 'G'=92 up to 'G'=~95, and given that it still knocked, it means I need to boost the octane to G=~98-100 to give it the equivalent of R=~102.

p.s. I meant to write more about octane. Last night Shane in Oz sent me the link to a Land Rover manual that describes how to change the timing of two of their engines to deal with lower octane fuel. The manual gives two timing figures for one of the engines when it has the "high compression" 8.0:1 piston, but only one figure for the other engine with its 7.8:1. However, it gives several timing figures for both when using "low compression" 7:0 pistons.

Starting with 90 octane as the "normal" fuel (which I assume is the Research octane no.) and with the 8:1 piston, the 6-cyliner engine is to be retarded by 3-deg. when using 85 octane. Only the timing value for 90 octane is given for the 7.8:1 piston in the 4-cyclinder engine.

With the optional "low compression" 7:1 pistons Land Rover seems to assume the best either engine ever will see is 83 octane, and with respect to that fuel they're to be retarded by:

4-cylinder engine (with respect to 83 octane):
3-deg. with 75 octane

6-cylinder engine (with respect to 83 octane):
2-deg. with 80 octane
4-deg. with 78 octane

Although these values can't be applied to a Gold Star engine, they do show that a fairly large drop in octane (e.g. from 83 to 78 or 75) doesn't require the timing to be retarded by a huge value. On the other hand, not knowing what the fully advanced timing values are for these engines, these 3-4 deg. changes could represent a pretty significant fractions of those values.

Posted By: George Kaplan

Re: Correct needle for 1000-series Concentrics? - 06/11/19 5:26 pm

Thanks for this MM, i have learnt something. As they say we are two countries separated by a common language. (I am stretching it a bit by applying "language" to other ways that we describe things like octane ratings or gallons)

In the interest of knowing a little more I found some articles online including a Masters Dissertation titled Effect of spark advance and fuel on knocking tendency of spark ignited engine

John


Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/12/19 4:57 am

Originally Posted by George Kaplan
... knocking tendency of spark ignited engine
The expensive stuff that I'm waiting for to arrive is called Race Gas and on their site I found the attached chart. As can be seen they estimate 10:1 needs 100 octane, and also that I would have to drop down to 8:1 if I hoped to use straight 92 pump fuel. If the Race Gas works, that will be my Plan A.


Attached picture RaceGas_CR_octane.jpg
Attached picture RaceGas_CR_octane_2.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/12/19 6:50 am

Have worked with MON and RON and the average of the two over the years, when considering high performance competition 2 strokes..easy to get the fuel/compression wrong and you will have an expensive seizure..

Broad-brush 'conventional' wisdom says compression needs to be no more than 10% of the octane rating (being non-specific about which version of octane rating)...hence my earlier post about a max of 9:1 on 92 and probably less (especially given the old-style combustion chamber design).

It is also my experience that some/many octane improvers don't achieve much, especially where they don't contain lead. As they don't, if they want to be acceptable in street engines in most of the western world these days.

Fuel quality, as a function of time and handling, is also a factor: that tin of gas that goes 'whoosh' when you take the lid off is less of a fuel than you might think..the whooshing bit is all the stuff that makes it good. We've all heard how the fuel goes off over time, with the light ends (the whoosh) evaporating and reducing the fuel quality. It's true - read up on Reed Vapour Pressure. Had this experience driven home to me in recent times, where the fuel had lost all it's whoosh and was consequently harder to vaporize in the engine (effectively coming out of the needle jet in bigger 'globs' than normal, which are consequently harder to vaporise). The end result is that the spark plug (and presumably any air-fuel sampling device) sees rich, though the combustion is actually lean...so the tuner goes smaller in the jetting..worsening the problem.

Kerry W

PS: sometimes simply backing the spark off is no more than a band-aid..the compression needs to be right for the fuel
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/12/19 5:06 pm

Originally Posted by Kerry W
my experience that some/many octane improvers don't achieve much, especially where they don't contain lead. As they don't, if they want to be acceptable in street engines in most of the western world these days.
Right. I'm generally skeptical of snake oil, although overall I'm a believer in Monsanto's old slogan of "better living through chemistry." That's why I've tried to qualify my comments about the octane booster I used by writing 'if it worked', and the stuff I have on order with 'if it works'.

Originally Posted by Kerry W
high performance competition 2 strokes..easy to get the fuel/compression wrong and you will have an expensive seizure..
Another important factor is temperature. I reported my jetting results as having been made at an ambient temperature of 95 oF because that matters. My friend whose shop burned down was an active AHRMA competitor in the '90s and '00s on his now-destroyed Yamaha 350. Since in principle he might race one weekend at Willow Springs, California at 95oF and the next weekend at Steamboat Springs, Colorado at 65 oF, I realized he would get more practice time at the second higher, colder track if he needed to spend less time sorting out the new jetting.

It turns out that fuel flow depends on the ratio of density to viscosity, and both of these properties change with temperature. So, using a Cannon-Femke viscosimeter and Ertco hydrometer I determined these to 0.2% between 32 oF and 120 oF for VP C12 racing fuel. Making a long story short, I then created a kit containing the instruments for measuring the necessary parameters (relative air density, temperature, humidity, etc.) and devised a program for a portable calculator that used all of these inputs to convert the presumably-perfect main jet determined at one race to the required main jet for the current track.

Returning to my Competition, fuel flow at 95 oF is ~35% greater than at 65 oF which, of course, will affect the jetting. Unfortunately, it's more complicated than simply measuring the ambient temperature since what matters is the temperature of the fuel in the float bowl (which can be measured, but with more effort). But, without being quantitative, it's safe to say that, all other things being equal, more fuel will flow on a hot day than on a cold day. It's also safe to say the air density will be lower on a hot day than a cold day, which means that both the total amount of air ingested by the engine, and the "vacuum signal" at the top of the spray tube that draws fuel in, depend on temperature. As I said, it's complicated.

Originally Posted by Kerry W
Fuel quality, as a function of time and handling, is also a factor: that tin of gas that goes 'whoosh' when you take the lid off is less of a fuel than you might think.
I was interested in 'the whoosh effect' in the context of determining whether or not fuel stabilizers made any difference. So, in the '00s one long-term test I conducted was of the volume of fuel lost as a function of time. In an open container at 72 oF fully 50% was gone in just three days. While that's not too surprising, 1.9 years later -- hey, I said it was a long-term test -- a small quantity still remained of a very viscous liquid.

Originally Posted by Kerry W
the spark plug (and presumably any air-fuel sampling device) sees rich, though the combustion is actually lean...
Bosch wideband sensors are sensitive only to the oxygen and they produce a voltage proportional to the difference between the percentage of oxygen in the exhaust pipe and that in the outside air. All the sensor "knows" is how much oxygen is present, not how it got there, so there are circumstances when interpretation of that result as rich/lean mixtures can go awry. For example, if an engine misses, oxygen doesn't get combined with the hydrocarbon so the sensor sees too much 02 which the meter incorrectly displays as a lean mixture.

No matter how bad the fuel is, if it burns, the oxygen sensor contains information about the rich/lean mixture strength. That said, "classic" gasoline combines with all the oxygen if the AFR is 14.7, but I don't know if that same 14.7 applies if, say, a lot of the 'whoosh' was gone from the fuel that burned. If the stoichometric ratio of de-whooshed classic gasoline is different than 14.7 then interpretation of the mixture strength from the output of the sensor will be affected.

Octane, compression ratio, ethanol content, timing, temperature, density, air/fuel ratio,... It's remarkable carburetors and engines work at all, let alone that they work so well.
Posted By: Belfast Bikes

Re: Correct needle for 1000-series Concentrics? - 06/16/19 5:20 am

You have "optimized" the AFR for efficient combustion, but running under load using pump fuel in our deep chambered, low energy ignition dinosaurs presents another challenge . Enriching the AFR beyond the modern norm might reduce pinging under load.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/16/19 6:51 am

I have no definitive data, but the norm seems to be to retard a few degrees (say, 3 or 4) when running modern, fast(er) burning unleaded fuels.

My lack of data relates more to how much 'too far advanced' and engine would be to pink/ping (depending on where you grew up). I'd suggest that it's probably more than 3 to 4 deg, though while retarding by a few degrees might raise the 'ping threshold', adding fuel, as suggested above, would definitely help - though a compression plate or a few mm off the piston crown is the real answer.

My father and I were in exactly this position with a little air-cooled twin cylinder 125cc Yamaha factory-produced road-racer about 35 years ago - the PO could not stop it seizing and concluded compression was a problem, so fitted 2 head gaskets (it used a little copper gasket). This din't help much. Preference at the time was to use 96 octane pump gas, which you could get away with in up to a 125cc cylinder, because it mixed easily with the preferred Castrol R bean oil. The better fuel (though slow burning) was 100/130 green avgas, readily available, more expensive and didn't like mixing with the Castrol R without a large dose of acetone..which was more of a problem to find.

I the end, we ran the pump gas, backed the timing off from 2.0mm BTDC to 1.85mm (0.006" at the piston), ran the stock single copper head gasket and pushed the jetting up a couple of sizes. On the coldest plugs we could find at the time, (Champion N55G's - approx the same as an NGK B10 or 10.5) it ran like a train..the only time I ever seized it was own I ran it on some soft plugs and forgot to change them for the race..

In this case, the compression was workable for the fuel, but needed less timing and richer jetting to keep it in one piece. It would probably have run better with better fuel and more advance/leaner jetting..though it did get me to score some points in the national 125 series at the time..probably the last time it was done on drum brakes and 5 speed with air-cooling! (about 1984..the bike was 1974..)
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/16/19 2:10 pm

Originally Posted by Belfast Bikes
Enriching the AFR beyond the modern norm might reduce pinging under load.
Originally Posted by Kerry W
a compression plate or a few mm off the piston crown is the real answer.
I hope to have the chance later today to try the bike with the new, costly octane booster. I'll also swap the main jet for a different one of the same nominal size to try to sort out the issue with variations in marked size.

What I won't do this morning is rebuild the engine with a lower compression piston. Instead, I'll ride with crossed fingers hoping that, plus the octane booster, provides a workable solution.
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/16/19 2:18 pm

Ahh..the old fingers crossed option!

You'll be back..
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/16/19 2:20 pm

Originally Posted by Kerry W
Ahh..the old fingers crossed option!
Desperate times call for desperate measures...
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/17/19 12:12 am

Today's very good, albeit expensive, news is the 'Race Gas' octane additive actually works. I mixed 8 oz. into 2-gal. of 92 octane, which is supposed to boost it to 100. The only times I heard slight pinging/pinking was for the first half-sec. or so when pulling away from a stop sign going uphill without retarding the ignition, and for a half-sec. or so after making a slow-speed U-turn and pulling away in 2nd and again without retarding the ignition. It was 97 oF when I made today's jetting run, which pretty much counts as worst-case conditions for pre-ignition. This additive, although expensive, saves me from having to rebuild the engine and install an 8:1 piston in order to use 92 octane pump fuel.

The downside to 'Race Gas' is it costs $1/oz. ($32.49/32 oz.) so it adds $4 to each gal. of gasoline to bring it up to 100 octane, resulting in a total of ~$7/gal. at today's price at the pump (£1.47/l, AU$2.69/l). On the other hand, at ~50 mpg the additional cost to go 2000 miles only will be ~$160, which is a lot cheaper than rebuilding the engine. Another downside is when I know I won't be able to ride bikes for a while I empty the tank and dump it into one of the cars. That now becomes a much more expensive disposal.

Returning to jetting, you might remember that a jet marked '220' resulted in an AFR of ~12.3.:1 at full throttle, while one marked with a smaller '200' gave a slightly richer mixture of 12.0:1. I didn't have another '200' to try today so I installed a '190'. This resulted in a leaner mixture, as it should, but the 13.0:1 isn't quantitatively consistent with either the '220' or the '200' having been accurately marked (nb. none of them might be correct). That is, if the '190' happens to be a truly accurate 190, an accurate '200' should have given 190/200 x 13.0 = 12.3 instead of 12.0, and an accurate '220' should have given 190/220 x 12.3 = 10.2 instead of 12.3. However, as the saying goes, close counts in horseshoes, hand grenades, and Amal jet markings, so I conclude from this that the markings on the '190' and '200' are "essentially correct,", but the '220' is off by several sizes. Unfortunately, I had tossed it back in the '220' compartment a week ago where it is now mixed with others that might (or might not) actually be true 220s.

Using the Mikuni "Main Jet Tuning Calculator," if a 190 main jet is perfect at 100 oF, one that is one size larger would be needed if riding at 75 oF and two sizes larger at 47 oF. Stated the other way, the present '190' would be two sizes too lean at 47 oF, resulting in an AFR of 14.5:1 rather than today's 13.0:1. Instead, the '200' that was in it until this morning would give 13.5:1 at that too-cold-to-ride 47 oF, and 12.6 at 75 oF. So, I'll be re-installing the '200'.

I'll shortly be posting a full 1000-Concentric jetting guide with all the relevant results of these experiments. As a preview, for a fixed needle adjustment (middle slot), and within the normal variations of the AFR, the '190', '200' and '220 all gave the same results below ~1/4 throttle, with the main jet dominating above ~1/2 throttle. The effect of the needle can be seen in the shape of the curves between ~1/4 and ~1/2.


Attached picture AFR.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/17/19 2:12 am

So MM, what you're saying is that we can all send you out Amal main jets for you to calibrate using your AFR setup...generous! A big box on the way!
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/17/19 3:50 am

Originally Posted by Kerry W
what you're saying is that we can all send you out Amal main jets for you to calibrate using your AFR setup...generous! A big box on the way!
A high-born Indian colleague (younger son in the line of the only Indian ever raised to hereditary British peerage) told me a story of his time spent receiving his Ph.D. from Cambridge. His possibly apocryphal (or possibly autobiographical) story was that a high-born Indian joined a research group at Cambridge and, in what is a pretty common practice, was given an initial menial job to begin familiarizing him with the lab. He was to sort loose resistors back into appropriate drawers, but when the professor returned later in the day he saw the resistors still strewn across the table. When the professor asked why he hadn't sorted them the student replied "the boy never showed up."

Back to your box of jets. I'll be more than happy to calibrate all of them. As soon as the boy shows up...

If summer temperatures weren't coming on strong, and if I didn't have other things I wanted to get to (like re-rebuilding the Ariel), I'd be very tempted at this point to convert my 1038 to a full 4-stroke body and see how different its final jetting was from the 1036.

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/18/19 12:41 am

I had a second close call with the Sheriff. After getting a data point at 3/4 throttle I didn't have enough road left to get another data point (i.e. by holding the throttle at a fixed position for at least 4 sec.), so I shut down in order to do a U-turn early at an upcoming cross road. When I already had dropped to a slow speed a Sheriff's car pulled up at that stop sign and then turned onto my road. Only once today had I quickly glanced at the speedometer and saw I was only doing 40. It certainly felt faster than that but I dismissed it as the poor quality of the road and continued accelerating. Later I realized it was the tach I had glanced at so I had been going ~70 mph. If I had been doing a full-throttle run I would have been going at least that fast when I passed that cross street.

Originally Posted by Magnetoman
I'll shortly be posting a full 1000-Concentric jetting guide...
Correction, I should have written that I'll soon be posting that guide. I always hate it when I've disassembled some setup only to then realize there is one more measurement I wish I'd made. So, since there's no urgency to have the Competition in final form, and since the 'Race Gas' is working with its 10:1 piston (another 32 oz. of which is on order), it was time for another measurement.

I had thought raising the needle another notch would make it too rich, but I decided I needed to find out for sure. So, I raised the needle to the bottom slot leaving the rest of the settings the same as yesterday. Also, what is important for fuel flow is its temperature, not that of the air, so I measured the temperature of the fuel in the tank (~100 oF) and the outside of the float bowl (~100 oF), both of which were essentially the same as the air temperature. The dashed green curve on the attached figure shows the result of today's jetting run with the needle on the richest slot. Updated Figure: the AFR will stay between the green bands with the needle in the #3 slot in the temperature range 48oF<T<98oF.

While today's jetting is "too rich" for maximum h.p. between ~1/4 and ~1/2 throttle, the bike still ran great. Keeping in mind that at 68 oF the curves will be displaced upwards by AFR ~0.8 (and by twice that at 48 oF, a temperature at which only a Scottsman would consider riding), having the needle on slot #3 would ensure the peak always would be below 14.7. Also, during the nine months of my actual riding season, when the temperature is below 90 oF, the AFR would be no richer than ~12:1. So, I'm now tempted to leave the #190 in place and the needle on the #3 slot.

Any day now two 1000-Series slides should show up from England, which will give me a #2, #3, #3.5, #4 and #5 to work with, and I found an incomplete 1036 in the U.S. that tracking shows will be here on Wednesday. If it's in reasonable shape I'll drill out the compensating air passage and install a flat-top 4-stroke spray tube. That will enable me to make direct comparisons of the jetting needed for each carburetor body. The same person using the same motorcycle for all of these jetting studies eliminates a couple of big variables so the one (estimated) other person in the world who might care about these results can have confidence in them.


Attached picture AFR.jpg
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 06/19/19 7:52 am

Quote
I had a second close call with the Sheriff. After getting a data point at 3/4 throttle I didn't have enough road left to get another data point (i.e. by holding the throttle at a fixed position for at least 4 sec.), so I shut down in order to do a U-turn early at an upcoming cross road. When I already had dropped to a slow speed a Sheriff's car pulled up at that stop sign and then turned onto my road. Only once today had I quickly glanced at the speedometer and saw I was only doing 40. It certainly felt faster than that but I dismissed it as the poor quality of the road and continued accelerating. Later I realized it was the tach I had glanced at so I had been going ~70 mph. If I had been doing a full-throttle run I would have been going at least that fast when I passed that cross street.


He was probably an old time racer & wanted to soak up the glorious sounds of the bike on full song,,,,,, we hope.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/19/19 11:48 pm

Originally Posted by Magnetoman
Any day now two 1000-Series slides should show up from England, which will give me a #2, #3, #3.5, #4 and #5 to work with, and I found an incomplete 1036 in the U.S. that tracking shows will be here on Wednesday.
The 1036 was delivered a few minutes ago and, not only is it in good shape, it came with a #2.5 slide. So once the ones from England arrive I'll only need a #4.5 to have a complete set by halves from #2 through #5. Slowly, but steadily, I'm implementing my version of the underwear gnomes' three-step business plan to take over the world, except by cornering the market for 1000-Series Concentrics (Step 1, collect Concentrics; Step 3, take over the world -- like the gnomes, I'm still working on Step 2).

The carburetor is a 1036/11 but my lists only go as high as /8. The slide cutaway and jetting (and jet holder) that came in it are for a 2-stroke but, as can be seen, the spray tube is notched like the ones in the 932s used on Norton 850s. Fairly little information on the 1000-Series is available so this Nortonesque spray tube raises questions for which I'm not aware of the answers. Is the spray tube stock, or a user "upgrade"?

I'll install a 4-stroke spray tube, drill out the compensating air passage, and configure it with the same settings that are listed for a Thruxton. That should get things pretty close for the Gold Star. It's going to be very interesting to compare the final AFR vs. throttle position curves of the two carburetors.

Update: the seller responded to my question saying he doesn't know what bike the carburetor came on, but that he bought it along with other parts from "an old flat tracker who ran Triumphs and Nortons." This doesn't answer the question, but does increase the odds a little that the spray tube was an "upgrade" rather than being factory-original.


Attached picture 1036SprayTube.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/20/19 3:43 am

This will be, thanks to MM's efforts, the real answer to the question - not whether the 2 stroke carb can be made to work on a 4 stroke, but what the differences are between 2 and 4 stroke carb setups for the same bike.

Go to it!
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 06/20/19 4:09 pm

Not so fast on claiming you are cornering the market on 1000 series concentrics.

I have from 1034 - 1038 and in some cases, more than one of each size.....

Just sayin'

laughing
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/20/19 6:55 pm

Originally Posted by Rich B
I have from 1034 - 1038 and in some cases, more than one of each size.....
This doubles the number of people potentially interested in my jetting results. Now there are two people: you and Kerry.

I decided I need to make one more run with the current carburetor, with the '200' main jet replacing the '190'. I made the swap so the bike is ready but probably am not going to have a chance to make that ride until tomorrow. Meanwhile, though, I modified the 2nd 1036 to turn it into a genuine 4-stroke body.

The first photograph shows the drift ready to push the 2-stroke spray tube out of the body. The OD of the tip of the drift is 0.246" in order to slip into the 1/4" ID of the spray tube, and the OD of the main part of the drift is 0.309" to fit through the 5/16" ID hole in the body.

With the old spray tube out of the way, but before pressing the replacement into place, I then drilled the restriction out of the compensating air passage using a #10 bit (0.1935") as shown in the second photograph. After doing this and cleaning up the swarf I pressed the 4-stroke spray tube into place.

Although the carburetor appeared to be very clean when I got it, taking no chances I inspected the pilot jet passages. It's a good thing I did because the chamber under the two pilot holes held quite a bit of some unidentified fuzzy material as shown in the third photograph. I blew it out from the front of the carburetor through the hole for the adjusting screw. I then dropped #80 drill bits into the pilot holes to be sure they weren't blocked, as shown in the fourth photograph.

I have a ring light on my garage stereomicroscope which is great for most things, but not for illuminating deep holes. By manipulating a flashlight I could see into the cavity under the pilot holes where I didn't see any residue, but I couldn't hold the flashlight and take a photo at the same time so you'll have to use your imagination. To be certain everything was clean and unblocked, while holding the carburetor at an angle I filled the passages with acetone until it came out through the two pilot holes.

To minimize variables, after doing my next/final(?) run with the current carburetor I'll swap its complete float bowl, needle, needle jet, and needle jet holder, leaving the replacement #3 slide, main jet and pilot jet (and spray tube) as the only components that will be different. The #3 slide is a nice slip fit so this second body, like the first, shows no sign of wear.

Attached picture Concentric_Mod01.jpg
Attached picture Concentric_Mod02.jpg
Attached picture Concentric_Mod03.jpg
Attached picture Concentric_Mod04.jpg
Posted By: Rich B

Re: Correct needle for 1000-series Concentrics? - 06/20/19 11:49 pm

While 1 of my 1000 series carbs graces a Gold Star, and your work will likely encourage me to improve the 1038. You have already convinced me I am too rich on the slide, but I already knew that, but it ran good and I was a bit too lazy to improve it.

But, the bulk of my 1000 series carbs will remain 2 stroke carbs for 2 strokes. I have stupidly got involved with flat track again. Which in turn leads into getting a couple of vintage Bultaco flat track bikes running again. And I have a belief that jetted right, the Concentric is a bit easier on a high strung 2 stroke on a 1/2 mile. IME, the trick involves the pilot circuit.

Then there is the collection of large 2000 series carbs too.....
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 06/21/19 11:27 pm

Quote
This doubles the number of people potentially interested in my jetting results. Now there are two people: you and Kerry.


You do yourself a grand injustice good sir.
There are lots of people interested, however for most it can only be limited to interest, the 932 was over kill on the M20 so I can not see me putting a 1000 on it till I go batty & decide to attempt a land speed record.
Can't do it right now cause lake Eyre is currently full of water.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/22/19 12:25 am

I made my absolutely last AFR measurement on the 2-stroke body 1036 today (unless I change my mind and make more...), with the results attached.

The blue areas, determined using the Mikuni Main Jet Tuning Calculator, denote the limits that the peaks and valleys of the dashed blue curve will stay between if riding in the 50-deg. range between 48 oF and 98 oF. No human should ever ride outside that band of temperatures (or even near the borders of that band).

Given these results, and the fact the bike ran every well today with the '200', if I end up "permanently" installing the 2-stroke version of the 1036 body it will be with the '200' jet in place because the health of the engine will be better if I err on the side of too rich rather than too lean. Of course, I certainly know I should change the main jet to compensate for the temperature and altitude. But, I'm too lazy to do that. I carried a range of jets with me on the Cannonball, but the Ariel crossed the Rockies with the same main jet as it had at the sea-level start and finish. If I were racing it would be different, but for civilian use 'perfect' is the enemy of 'good enough.'

After finishing the jetting run and analyzing this very last set of AFR measurements I'll ever make on the 2-stroke 1036 body (unless I make more...), I swapped the parts discussed in my previous post into the "4-stroke" 1036 and installed the slide, pilot jet, and main jet that Amal lists for the 1036 used on 1970 Velocette Thruxtons. The bike started immediately but the idle was much too high no matter what I did to the idle or mixture screws. I got the idle as low as I could and then made a lap of the driveway. This doesn't count as much of a test, but I felt no hesitation on acceleration so the cutaway seems correct.

I then removed the carburetor, tore it down, and installed a #25 pilot jet in place of the recommended #30. This time I dropped a slide in the other 1036, noted how far above the bore that the idle screw lifted it, and set approximately the same height on the "new" 1036 before reinstalling it. However, the smaller jet seemed to make no difference. In fact, I closed the mixture screw all the way and it still idled too fast. I removed the air cleaner to check if something was holding the slide from dropping all the way, but it was fine.

I tried to stay hydrated while working and riding today, but by the time the second pilot jet hadn't worked the combination of 100 oF temperature and gasoline fumes had given me a headache of 10 on the Richter scale so I called it quits for the day. I doubt if I'll be thinking clearly for some hours so I would greatly appreciate suggestions to help me locate the cause of a too-high idle.

p.s. In case it's relevant, the "new" 1036 has a small hole in the part of the casting where the tickler would be located if it were a RH version while the "old" one doesn't. Gasoline spurts from that hole when the carburetor is tickled (which is why I noticed it), but dribbles from the tickler on the "old" 1036.

p.p.s.. As a matter of possible interest, the third image is a ~30 second plot of the AFR after I returned from my last run with the 2-stroke body and let it idle without touching the throttle. It idled quite smoothly and regularly during those 30 seconds, but note how much the AFR wandered around.


Attached picture AFR_21June2019.jpg
Attached picture Concentrics.jpg
Attached picture Idle.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/22/19 5:53 pm

What a difference a not-headache makes. Re-examining the carburetor this morning I quickly found the throttle cable is taut and so it was holding the slide above the throttle stop. When I looked into the bore at the end of the day yesterday it only appeared to be going all the way down. This explains both the high idle and the way it responded to the mixture screw.

My problem now is that the #3 slide is an aftermarket brass one that, although it fits very well, possibly has the platform for the cable (and needle) a bit too low since after shortening the adjuster as far as it will go it still left the inner cable with tension on it. Another possibility is I didn't get the ferrule fully in the countersunk slot for it when I changed the slide (or the countersink isn't deep enough). No matter what, I'll remove the slide and make careful measurements of it vs. a genuine Amal one to also be sure having the needle on the #1 slot drops it into the needle jet by the same amount as if it were in an actual Amal slide. However, shortly we leave for a birthday party for my younger granddaughter so further carburetor work is on hold until tomorrow.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/22/19 11:49 pm

After performing lifeguard duty for a dozen screaming kids for two hours in the 98 oF sun we turned that part of the birthday chaos over to the parents and made our escape. Although it was too late to do much work on the bike, I needed to know what was causing the problem.

Originally Posted by Magnetoman
(or the countersink isn't deep enough
Bingo! Give that man a prize!

As the first composite shows, the soldered fitting on the throttle cable projects below the bottom of the brass aftermarket slide, but is well countersunk in the Amal. Measurement showed the Amal countersink is fully 0.168" deeper, explaining why the aftermarket slide didn't touch bottom yesterday. Or why the cable was still taut today even with the adjuster at the end of its range.

Although the countersink was made incorrectly, the second composite shows that the needle projects beneath the bottom surface by the correct amount to within a few thou., and the third composite shows the brass slide is only 0.016" taller than the Amals (since the needle projects the correct amount, the bottom is the correct height, which means the excess 0.016" needs to be trimmed from the top). At worst a too-tall slide would project slightly into the airstream at full throttle, although it doesn't appear the 0.016" is enough to cause this. However, since it's easy enough to do, and since I'll be drilling the countersink deeper on the mill anyway, I'll take this much off on the lathe tomorrow.

Related to Amal work, the 3½ and 5 slides from England arrived today. For future tuning work I now have a full set of 1000-Series slides from 2 through 5 by halves, missing only 4½.

Attached picture AftermarketAmalSlide01.jpg
Attached picture AftermarketAmalSlide02.jpg
Attached picture AftermarketAmalSlide03.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/24/19 2:45 am

The heights of four Amal slides all were less than that of the aftermarket slide so I skimmed 0.012" off the top to make it the same length as the tallest of the Amals, as shown in the first photograph.

Amal seems to have used a #29 (0.132") drill bit to make holes for the cable in the slide, but the holes in the brass slide were slightly larger at 0.138" so a 3.5 mm drill bit probably was used. Drill bits don't like to track straight in holes with slots on one side so I used a miniature 9/64" end mill (0.141"). The depths of the countersunk holes for the throttle cable were 0.302" in three of the slides and 0.294" in one of them so I increased the depth in the brass slide to 0.300" as shown in the second photograph.

With the deeper countersink the cable adjuster allowed a little slack so I installed the carburetor, started the bike, and now the throttle stop screw worked as did the mixture screw. I had changed back to the #30 pilot jet and the mixture seems best with the screw 1½ turns out.

If I had been thinking more clearly prior to my first jetting run today I would have realized the recommendations for the Thruxton probably assumed a temperature closer to 68 oF than to 98 oF which according to the Mikuni calculator means I should have started out with a 310 jet rather than a 320. to have the equivalent of Thruxton jetting. However, that wasn't my biggest problem today.

I had carefully put two larger jets, and two smaller, than the 320 in a plastic bag, and just as carefully left that bag on the workbench. I did, however, remember to pack the tools needed to drain the float bowl and change the main jet. So, after the bar display on the Innovate showed an AFR of ~10 on a full throttle run I stopped on the side of the road, drained the fuel, removed the 320, and only then discovered I didn't have the bag of jets in my backpack. So, I put the 320 back in the carburetor and continued on while concentrating on lower throttle settings where the main jet doesn't have much effect.

Unfortunately, the missing bag of jets wasn't my only problem. I use a 12V, 2.3 A-hr sealed battery to power the Bosch sensor, which draws 1 A. I deliberately bought a small battery that is good for somewhat over two 45-min. jetting runs to make it easiest to attach to various places on a bike. The low capacity is fine because the Innovate only records for 44 min. and it takes at least an hour to download and analyze a set of jetting data and make the necessary changes to the carburetor. That allows ample time to charge the battery back to full capacity using a 1.2 A Battery Tender. That is, if I remember to attach the charger. Which I hadn't. So, a few minutes after not changing to a smaller jet on the side of the road, the A/F meter showed the battery was too weak to continue powering the sensor.

Back at home I analyzed the ~20 min. of data that had been captured before the battery died and determined that if the 320 were correctly marked than a correctly-marked 270 would give 12.1:1 at full throttle. So, I swapped to one marked 270 and on the next run it gave 11.5:1 at full throttle, which is within what I've come to expect as the variation in the marked sizes of these jet. Although still a bit too rich at full throttle the data shows the mixture is too lean in the range controlled by the cutaway.

The easy part tomorrow will be to switch to a main jet marked 260, but it will take slightly longer to change the #3 slide to a #2.5. Fingers crossed that one more run will have the jetting for the 4-stroke body nailed down

Attached picture AftermarketAmalSlide04.jpg
Attached picture AftermarketAmalSlide05.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/24/19 11:41 pm

Even after many hours spent at the flow bench measuring a half-dozen carburetors having different spray tubes and air jets, and more than a dozen 30-min. jetting runs resulting in 150 pages of printouts that determine the AFR vs. throttle position with different main jets, slide cutaways and needle positions, I can't claim I know everything there is to know about Amals. But, I now have a much better understanding of what I don't know than I had a few months ago. I now know that I don't know things that a few months ago I didn't know there were to know.

One thing all the AFR data I've collected tells me is that anyone who says he can correctly jet a carburetor by looking at the spark plug has psychic abilities I don't posses. The complexity of the interaction between slide, jets, and needle position, and the fact the bike "feels" like it is running well for significantly different AFR values, means that no matter even if reading the spark plug gave a perfect value for the main jet,[*] that's only a single data point on a curve that undulates up and down in regions where that one data point has essentially no effect

[*]That's assuming the full-throttle plug-chop that was used to give a perfect reading the plug was done only after the bike had reached near maximum speed. If the plug-chop is done even after reaching 75 mph the AFR would have been still dropping so the plug reading would have given an erroneously lean result for the mixture.

Over the past weeks I've determined that my Gold Star starts, idles, accelerates, and runs well for AFRs that can be anywhere between 10:0:1 to 15:0:1 for a given throttle setting. Even if the main jet were perfect, only if the seat of my pants were calibrated a lot better than it is could I hope to say based on how it "feels" whether the AFR at, say, 1/4 throttle were 15:1 or 11:1. As an example, at the end of today's run I let the bike idle for 40 sec. without touching the throttle. The seat of my pants told me it idled smoothly the entire time. However, the attached graph shows the AFR varied between 11.3 and 14.4 during that time.

I left the #3 cutaway in for the moment, but today's jetting run was a disappointment in that the '250' main jet I put in this morning turned out to be slightly leaner at full throttle than the '260' it replaced (despite which, the seat of my pants told me it ran great with both main jets.). Aside from the annoyance of Amal jets "never" flowing what their markings say they will, the issue I want to address is it goes very rich (~10.5) over a narrow range of very small throttle settings, but then goes through a lean-ish (~14.0) peak at ~1/4 throttle. The half-size smaller cutaway I had planned to install today was to address the lean-ish peak, but it would make that too-rich valley even richer.

I'll give this some more thought before deciding what to change next. Unfortunately for me, the forecast shows a steady climb to a high of 107 oF by Friday, where it will plateau for a few days, and the long-term forecast shows it no lower than 101 oF for the next two weeks. Those of you who have never experienced riding in desert air above 100 oF can simulate the feeling by holding a hair dryer on 'high' a few inches from your face. Once your body is perspiring as fast as it can, going faster only makes it worse since your internal cooling mechanism is already maxed out.



Attached picture Concentric_Idle02.jpg
Posted By: Kerry W

Re: Correct needle for 1000-series Concentrics? - 06/25/19 12:14 pm

I have to say that, with the advantage of time zones (I'm 12 hours ahead of the US West Coast), this thread is my first port of call when I get up in the mornings!

I've always been keen on getting carburetion right and have long believed that the seat-of-the-pants assessment is little more than a go/no-go gauge, in terms of gross assessment of direction of change and the owner of the pants is unlikely to notice less than 10% differences between setups, whien using the 'concrete dyno'.

I had an instance a few years ago where I was running a 4 cylinder 750cc two stroke road-racer that I knew made 120hp at the rear wheel. For originality, when the rings needed changing (at 250 miles!) I reverted to that bike's original 700cc cylinder setup, which was supposed to make 90hp, ex-factory. Keeping the same ignition, exhausts (aftermarket) and carbs (rich), with some subtle piston mods, the bike made 118hp on the same dyno, though with much better mid-range power than the full 750cc setup.

Riding the bike (despite it being no slower, pulling hard through 170mph), the rider perceived the bike to be SLOWER in acceleration...all because the torque and HP curves were a better shape and had less 'step' onto the power, making the acceleration seem less aggressive. We knew from the dyno what the real story was. Actually, the bike would have been faster around a given road circuit as the modified 700 than as a full 750, all due to the piston mod-inducing mid-range go, despite all the 'wisdom' saying that the later 750 version cylinders made more power (certainly true if apples are compared with apples; the mods to the pistons in the 700 cylinders have ben incorporated on the full 750 pistons to get the 'full effect'...I should know how much in a few months!..I'm betting on 130+ hp..low numbers these days but exciting enough in a bike that weighs less than a GS)

The point of my tale is that perception is not foolproof and can be misleading, though, with effort, good carb setup can be achieved (perhaps with a stopwatch). However, the knowledge and effort of definitive data like MM produces is the gold standard. Solutions to problems where most of us didn't even appreciate the problem!

KW

Posted By: Cyborg

Re: Correct needle for 1000-series Concentrics? - 06/25/19 3:55 pm

Reminds me of a story about Nicky Hayden when he went for the first couple of laps on the RC51. When asked what he thought, he mentioned it could use a bit more power. Then they showed him the lap times.

Also reminds me of the 1/4 mile times of a Yamaha RD 400 and a Honda 400 Hawk.

Seems like a subject that is so misunderstood.
Posted By: koan58

Re: Correct needle for 1000-series Concentrics? - 06/25/19 5:49 pm

The AFR graph at idling is interesting to me, and I assume that you find some interest in it as well, as you took the trouble to post it. Thanks.
I enjoy speculating.
It is a small sample to draw much in the way of inferences from, but there is a suggestion of a fundamental variation with a period of ~20 sec, with a higher frequency variation imposed upon it.

At such a minimal fuel demand, I suggest that the float mechanism reveals its resultant hysteresis on the fuel level.
The fuel demand is in (relatively) infrequent pulses, which may be followed by a return "after-pulse" back into the carb.
The float needle is likely to be opening and closing under these influences (as contrasted with the needle hovering at varying lift from the seat at higher fuel demand). Hence the hysteresis in fuel level, as the float mechanism can only act after the event and likely allow a bit more than necessary to pass the needle before it shuts.

This hysteresis in fuel level will be reflected in the AFR, and perhaps superimposed will be the individual draws of the induction strokes (and brief pressurisation of the bowl by return pulses, if any).
The latter ~20 sec of your plot does fit over the first half, in a loose fashion. The general trend seems evident.
Assuming a 1500 rpm idle for illustration, those 20 sec have 250 induction cycles. The graph is of insufficient resolution to observe on that scale, what impact if any the induction has upon fuel level, and then its impact upon successive induction mixtures.
I doubt that this is of more than academic interest, as the float needle will be acting far less hysterically when larger flows are going through it. The valve will then be open all of the time, just varying in opening in response to the amount of fuel level drop (and consequent float drop).

At the end of the day, I think there will always be a delay between demand (say opening throttle from half to full) and the fuel level dropping enough to open the valve sufficiently to equal flow demand. Carburettors will always be playing catchup in fuel level, fortunately it isn't too critical in most situations.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/25/19 6:03 pm

Originally Posted by Kerry W
...this thread is my first port of call when I get up in the mornings!
...Solutions to problems where most of us didn't even appreciate the problem!
Thanks very much for your comments. This thread is a result of someone with a long career in experimental physics and instrumentation who is (mis)applying that background to the study of obsolete... er, I mean, to British motorcycles. Also, not sponsoring a race team or selling anything means I don't have any motive to keep my findings secret.

If I only wanted my Gold Star to run well I would be done by now. Unfortunately, I also want to understand why, and that takes instrumentation and time.

Originally Posted by Kerry W
Riding the bike (despite it being no slower, pulling hard through 170mph), the rider perceived the bike to be SLOWER in acceleration...all because the torque and HP curves were a better shape and had less 'step' onto the power, making the acceleration seem less aggressive. We knew from the dyno what the real story was.
In principle, having AFR=12.5 at all throttle positions would result in maximum h.p. at each setting. Thus far I've concentrated on collecting AFR data at fixed throttle settings, not throttle response data, but the attached graphs illustrate an important difference between fixed settings (and dyno data) and performance on the road.

The first graph shows AFR in purple and throttle position in red for a 13-sec. interval yesterday. Full throttle is 1.5 V so the ~0.2 V peak at 9:25 is ~1/8 throttle. The second graph just expands the time scale. Without describing all the data on this graph in detail, one segment of it shows I started rolling on the throttle at 9:24.4 and had it fully at the 1/8 value by 9:24.9, i.e. 0.5 sec. later. However, the AFR data shows there was a delay of ~0.5 sec. between changing the throttle and response of the AFR. A half-second doesn't sound like much but it's a lifetime on the racetrack. And, on the street, if my engine had hesitated for 0.5 sec. instead of responding smoothly every time I changed the throttle it would have made for an awful ride.

I didn't have the tach hooked up for yesterday's session but I'll guess from the throttle setting that the engine was at ~2500 rpm, which means it fired ~10 times in that half-second. The response time of the sensor is faster than 0.1 sec. so, taken together, this means the carburetor is to blame for the delay in response of the AFR to the change in throttle. This "transient response" behavior of a carburetor is just as important as having the correct AFR at steady-state fixed throttle settings.

Anyway, in case anyone has followed along this far in the discussion, a dyno session could determine the AFR under load at 1/8 throttle and 3/16 throttle. However, what also is important on the road is how the engine responds when the throttle changes between those two settings, not just when going up a steep hill (roughly equivalent to a dyno measurement), but also how it responds on a level road as well as going downhill, each of which will have different AFR values at the same steady-state throttle setting. Also important for good behavior on the road is how it responds if a change is made in 0.1 sec. or 1 sec. Although not too much time at a racetrack is spent going downhill at 1/8 throttle, the same considerations apply at larger throttle settings.

To a large extent the response time of a given carburetor is fixed by the design of that carburetor. However, although I have a GP, 1038 Concentric, and 38 mm Mikuni on the shelf, for reasons I'll skip for now I've arbitrarily decided on a 1036 so I have to deal with its fundamental limitations instead of those of other carburetors. But, what my ~5+ hours worth of measurements on the 1036 indicate is tradeoffs can be made between AFR in a given range and throttle response in that range. I'm sure I'll have more to write about this in some future post when I turn my attention to transient response measurements.

By the way, I'm not saying there's anything wrong with dyno measurements, just that conditions on the road aren't the same as in a dyno cell. On the other hand, an advantage of dyno measurements is you don't have to worry if a sheriff's car might be around the next bend.

Attached picture AFR_response01.jpg
Attached picture AFR_response02.jpg
Posted By: NYBSAGUY

Re: Correct needle for 1000-series Concentrics? - 06/25/19 7:36 pm


Re Nicky Hayden, I may have this wrong, but I think Jeff Smith had a similar experience switching from the 500 Gold Star to the smaller lighter 440cc Victor. He got off his test laps on the smaller bike and said, "No effing good, give me back my Gold Star'. Then they showed him the lap times. End of an era.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/26/19 9:43 pm

It was going to be over 100 oF today, but despite my better judgement.. OK, scratch that, I'm working on a 60-year old motorcycle rather than doing anything even remotely useful so clearly 'judgement' is lacking.

If the '260' jet in the previous full-throttle run could be trusted as having been accurately marked then I should have installed a '220' or '230' today. But if the '270' in the run before that could be trusted then the '260' would have worked yesterday rather than giving an even richer full throttle AFR than the '270'. Anyway, I got a fairly early start before it was too hot, dropped the main jet to '250' and swapped the #3 cutaway slide for a #2.5. Which brings us to the next installment of "Bet You Didn't Think You Needed to Worry About That."

The first photograph shows that when I installed the #2.5 slide in the carburetor the needle wasn't hanging straight down from it. I might have been able to shove it sideways far enough to insert into the jet but that would have left the needle constantly rubbing one side of the jet rather than rattling around and bashing all sides as Amal intended.

The second photograph shows that the hole for the needle was drilled at an angle. How this could have happened is not explained by the measurement shown in the third photograph. With the slide held in a jig so as not to rely on the end of it being perpendicular to the sides, and the gauge zeroed at the front of the slide, the rear of the slide is higher by 0.013". However, that isn't sufficient to quantitatively explain the measured tilt of approx. 0.15" out of 2.5" = 3.43 deg. Further, the gauge found no difference in height from side-to-side while the first photograph shows there's definitely tilt in that direction. But, irrespective of how Amal screwed it up, it needed to be unscrewed.

Drill bits tend to follow existing holes so as the fourth photograph shows I first used a 7/64" (0.109") miniature end mill to straighten the hole and then a #32 drill bit (0.116") to make it the correct diameter. The needle itself is 0.098". Note that the fixture holding the slide is sitting on parallels to ensure the hole is precisely perpendicular to the sides of the slide.

Despite the machining, the needle still had a slight forward tilt when I did a test fitting in the carburetor. This differs from bench measurements because when installed the spring presses down on the needle clip. I already had measured the face against which the needle clip rests and found it properly perpendicular to the bore, and there were no burrs on the edges to interfere with the clip seating fully, so the problem had to be caused by the clip itself.

The fifth photograph shows three clips, two the same shape with the color of copper and of steel, and a third at the upper left with a different shape. It was over 100 oF by the time I found that the third type worked perfectly so I didn't try to figure out what subtle difference in the clips was causing the problem. I installed the slide, bolted the carburetor back on, and am now inside the air-conditioned house typing this. The next jetting run will have to wait until the relative cool of tomorrow morning.


Attached picture ConcentricSlide25_01.jpg
Attached picture ConcentricSlide25_02.jpg
Attached picture ConcentricSlide25_03.jpg
Attached picture ConcentricSlide25_04.jpg
Attached picture ConcentricSlide25_05.jpg
Posted By: Cyborg

Re: Correct needle for 1000-series Concentrics? - 06/27/19 3:00 pm

Good thing you have the tiny end mills so you can carve out some accurate clips that centre the needle.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/27/19 8:03 pm

Originally Posted by Cyborg
Good thing you have the tiny end mills ...
One cannot have too much tooling for a lathe or mill. I'm not sure which would have been worse, not knowing miniature end mills exist, or knowing they exist but not having a set of them when I needed one. I've found that no matter how much dust any piece of uncommon tooling collects on the shelf it always will be needed for some unusual task.

Aside from manufacturing defects, such as having the hole for the needle drilled at 3.4-deg., it would make setting up a carburetor ever so much easier if Amal had stamped numbers on the main jets that were somewhat exact rather than crude approximations.

I made progress with today's jetting run, but there's still more work to do. For future reference, changing from a #3 to a #2.5 slide enrichens the mixture by fully 2-2.5 AFR units from just off idle up to ~0.3 throttle (e.g. dropping the AFR from ~13.5 to ~11 at 1/8 throttle). Unfortunately, the #2.5 made it much too rich from just off idle up to ~1/8 throttle, while I needed a richer mixture only starting at ~1/8 throttle and from there up to ~1/3. So, my next attempt will be back with a #3 but with the needle raised one notch. Today's results showed the present '250' main may be OK, but it might need a '240'. See the next paragraph for an explanation.

As for determining the main jet size, assuming someone could accurately decide if the mixture was too rich, too lean, or just right by reading the color of a plug, how should a plug chop be done? We know to give the engine full throttle for some length of time, then simultaneously hit the kill button and pull in the clutch. But, for how long do we need to keep the engine at full throttle before doing the chop in order to get an accurate value? Prior to starting all these jetting runs I would have thought that 15 sec. of full-throttle in 4th gear headed up a hill until reaching ~5000 rpm and ~75 mph (in a 35 mph zone...) would have been sufficient, but the A/F meter tells a different story. As the attached graph shows, the AFR was still dropping under those conditions and thus a plug chop would have been at a point where the mixture was leaner than it eventually would be if given more time to reach even higher rpm (and higher speed). For more than one reason, I suspect for determining main jet sizes that many plug chops may be only slightly more reliable than reading Tarot cards.

I managed today's run while it was still in the 90s, but the high will reach 106 oF. The next three days will be even worse at 107-108. In order to do a run tomorrow I'll have to get started in time to swap the slide first because already it's too hot to consider doing that today.

On a final note, Amal's settings for the 1036 on a 1970 Velocette Thruxton include a 320 main jet, #3 cutaway, and needle on the top, #1, slot. Although I'm still not quite at the final configuration of the "4-stroker-erized" 1036 body, I'm close enough to compare the results. I'll go out on a limb to say that nearly all 1036s were made for 2-strokes, but based on my measurements that Amal supplied Velocette with a "4-stroke" version, i.e. with flat spray tube and no restriction in the air jet passage.

Attached picture AFR_FullThrottle01.jpg
Posted By: Cyborg

Re: Correct needle for 1000-series Concentrics? - 06/27/19 9:03 pm

Just a guess because it’s been decades since doing plug chops. I gave up when jetting a Kawasaki triple with expansion chambers and I was not so blissfully unaware that I was being chased by the local constabulary. No mirrors and couldn’t hear the siren..... anyhow... thinking in a lot of cases plug chops are pretty much pointless simply due to questionable fuel quality and varying quantities of ethanol.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/28/19 12:09 am

To add some information about the AFR range over which the Gold Star seems to run fine, the attached graph pieces together two ~30-sec. time segments from today (i.e. #2.5 cutaway) when I was following a line of cars down a hill for over a mile at ~40 mph. Because of the speed I probably was in 4th, but because of the hill I hardly had to use any throttle to maintain my speed. Note that when the throttle position sensor was above ~0.1 V the AFR was well behaved even at a very rich ~9.5:1, but when the throttle dropped below that value (i.e. barely above idle) the AFR became squirrelly.

The behavior near times of 22:05 and 22:30 wasn't due to the engine missing, because that shows up as sharp spikes to much higher AFR values, so it probably was incomplete combustion. I could feel the engine not behaving quite right a few times when coming down that hill with the throttle barely open but, other than those times, the bike seemed to run great today and was responsive to the throttle.

The point of this is that from these and other measurements I've made, as long as the mixture is within the range ~9.5-~16 the bike feels like it's running great. Without the ability to measure AFR I wouldn't have any idea what is actually going on in the combustion chamber.

I will be very interested to see what the Innovate tells me about the jetting in the BB and Catalina, both of which feel "perfect." However, those measurement almost certainly are going to wait until temperatures drop in the fall.

Attached picture AFR_27June2019_LowThrottle.jpg
Posted By: slow learner

Re: Correct needle for 1000-series Concentrics? - 06/28/19 3:59 pm

Pertinent to 1036s on Thruxtons; the Australian tech editor of the theirl Velo club, in the compilation of his articles " Norm's Technicalities", says he has encountered Thruxtons that came equipped with two stroke configuration carburetors. His assessment is they work fine as long as you do not mix four stroke and two stroke parts. The basic settings do not vary between the two versions.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/28/19 5:57 pm

Originally Posted by slow learner
the Australian tech editor... assessment is they work fine as long as you do not mix four stroke and two stroke parts. The basic settings do not vary between the two versions.
My flow bench measurements show that if Amal's recommended 320 main jet is correct when in the 4-stroke body, it would flow the same as a 390 in a 2-stroke body. Stated differently, if the 320 jet gave 13:1 at full throttle in a 4-stroke body it would give 10.7:1 in a 2-stroke body.

At 1/4 throttle, where the slide cutaway dominates, using the same #3 slide in a 2-stroke body would increase the richness by 17%, equivalent to increasing the richness from 13:1 to 11.1:1. I didn't do any measurements with the needle in the Thruxton #1 slot so I can't comment on that.

Although my measurements on the Gold Star show the bike doesn't exhibit obvious problems over a wide range of AFR, that's not the same as claiming "the basic settings do not vary" between the 2-stroke and 4-stroke versions of the body. They certainly do. By a lot. "Seeming to work fine" isn't the same as "actually working fine."

On a different note, I might have commented on it before, but the Eddie Dow TLS with Vintage Brake linings on this bike is the closest thing to having a front disk that anyone could hope for.

p.s. my younger granddaughter had an end-of-summer-camp dance recital at this morning and by the time I got home it was already 105 oF. Despite that, since I've done it enough times I could do it blindfolded (but please don't test me on that), I removed the carburetor and swapped for a #3 cutaway slide with the needle now on the 2nd slot and a '240' main jet. After lunch when it's up to 106 oF I'll do a jetting run... just kidding, no way am I riding at that temperature. Tomorrow there won't be a dance recital so I'll hope to get on the road before the snow melts.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/28/19 11:26 pm

Originally Posted by BSA_WM20
the 932 was over kill on the M20 so I can not see me putting a 1000 on it
I think you underestimate how much the lack of a proper carburetor is restricting your M20's h.p. potential. Yesterday a friend gave me a box of a half-dozen small Amals, one of which is marked '41 M20. As the attached shows, with a 1036 from a Gold Star your M20 no longer would have its h.p. restricted by only breathing through the tiny main bore, it also would get additional air from the mounting holes. Since both engines are 500cc I'm sure you can find the necessary adapter from one of the usual suppliers.

Attached picture Amals_M20_1036.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 06/29/19 8:47 pm

Mission Accomplished. It was 101 oF when I made the jetting run this morning so the snow plows already had cleared the streets and were nowhere to be seen.

After reviewing, and revising where needed, today's and previous results, the first graph shows the best jetting I found for 2-stroke and 4-stroke Amal 1036s after ~15 jetting runs covering ~200 miles and resulting in ~160 pages of printouts. More -- much more -- information about these carburetor bodies and jetting will be in a forthcoming multi-part thread.

Keep in mind that at a more human ~75 oF the equivalent main jets would need to be one size larger to give the same results. Or, keeping the same jets, the curves would be ~0.5 AFR leaner.

From my full-throttle flow bench measurements I would have predicted that given an accurate '200' main jet in the 2-stroke body, it would have taken an accurate '255' main jet in the 4-stroke body to give the same AFR at full throttle. Given the issues already noted with the marked sizes of Amal main jets, the results on the graph have to count as in excellent agreement with the flow bench measurements. If the two jets were actually 193 and 248 (i.e. less than one size off from the marked numbers) the agreement would be perfect.

It's not clear to me that the "flatter" overall behavior of the 4-stroke curve gives it any sort of performance advantage. However, although both versions of the 1036 body work well on a Gold Star the 4-stroke version does have the advantage of being leaner (but still rich enough) at nearly all throttle settings so it would be less damaging to the wallet. As a very rough estimate, if most riding is done between 1/4 and 3/4 throttle the fuel savings with the 4-stroke version will be ~5%.

The second graph shows that starting from near top speed in 1st it took 15 sec. at full throttle heading up a hill before the AFR stabilized at its final value. I was going over 75 mph at the end of that run which means during that time I covered ~1/4 mile. A shorter run reaching a lower speed would have given an erroneously high AFR reading.

Attached picture AFR_4stroke_2stroke.jpg
Attached picture FullThrottle_240Main.jpg
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 07/01/19 4:33 pm

Not to pick on him, but this post from two years ago illustrates an important point:
Originally Posted by Belfast Bikes
DBD Clubman ... Amal 1038 carb that is fully converted for four stroke use. The bike has a standard exhaust pipe and muffler,... a "minimalist" gauze type air filter.
... the bike runs well most of the time ... except at wide open throttle ... At that point, the RPM burbles and bobbles around 4500 to 5000 RPM, not 8-stroking and not surging, just hitting and missing until I close the throttle adequately to get things cooking again.
... current carb settings are: 35 pilot jet, 4-stroke 107 needle jet, 4-stroke (2-notch) needle in the richest position, 3.5 slide (a well-fitting, brass one), and a 4-stroke spray nozzle. I have tried main jet sizes from 330 to 430 ... all with the same result..
Even if "fully converted" really was the case, i.e. including drilling out the air jet passage, the smallest main jet he tried is 8 sizes larger than the one that my tests show would give the proper mixture in the cool air of Belfast. His smallest main jet would have resulted in an AFR at full throttle of ~9:1, along with the burbles and bobbles that come with being way too rich.

His use of a 107 needle jet along with the needle on the #3 position would have made things quite rich at lower throttle settings as well, only partially compensated by the weaker #3.5 slide. That his jetting worked at all is consistent with the fact my Gold Star seemed to run fine with AFRs anywhere in the range 10-15:1. This tolerance of incorrect mixtures also explains the fairly wide range you will find if you search for 1036 and 1038 jetting recommendations.
Posted By: Dave - NV

Re: Correct needle for 1000-series Concentrics? - 07/10/19 6:02 pm

Speaking of concentric carbs .. My departed friend GStar Ron (RIP) gave me the idea for a idle stop for the "smooth bore" racing carbs. Merely tapping the vent hole in the top of the slide and fitting a short #2 screw that protrudes into the inner with a locking nut on top works well after 'fiddling' adjustments for best idle speed. The end of the screw strikes the alu casting in the slide cavity. Make sense?

BTW, having a idle stop makes engine starting much easier vs trying to hold the throttle barely open.

Another issue on this carb Ron and I figured out, was the float bowl level running low especially when the fuel level in the tank was low. This condition will drive you silly especially when attempting to jet with a full throttle high speed run. We unsuccessfully tried drilling out the float bowl needle seat. Again Ron came up with good fix by ordering up the higher flowing alcohol float bowl from the UK Amal supplier. An expensive fix, but it works.
Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 07/10/19 9:01 pm

MM don't forget to use new, un-oxidized, main jets. As it is the leading edge of the jets orifice that is worried when the jets are sized with a polished burnishing tool. With very little oxidation, or
Bloom as Kevin Cameron likes to call it, accumulated on that leading edge of the orifice makes a big change in what the jet will flow.

The burnishing tool worries the leading edge, bringing the jet into size.

Jets sitting in a tool box for a period of time cannot be considered reliable as for the size originally marked on the jet.

In the old days Amal had two grades for jets, one for racing, and one for general street use. You could tell them apart where the street spec. jets have the annular
groove around the hex (similar to jets supplied under 376/100), and the racing (3326) ones the was no annular groove on the hex. After many years to oxidize, with any original 3326 racing main jet
it is only a guess how much fuel it will flow

If my memory serves me the racing were plus or minus 2.5%,
while the street ones we plus or minus 5% (but I could be correct on my % figures).

Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 07/10/19 9:49 pm

Originally Posted by John Healy
With very little oxidation, or Bloom as Kevin Cameron likes to call it, accumulated on that leading edge of the orifice makes a big change in what the jet will flow.
I'm quite skeptical of Kevin's Bloom Theory.(*) However, despite the recess at the outlet end, the edge of the hex of another jet can make physical contact with the orifice. Although jets tend to align themselves along the long axis where no such contact can be made, years of bouncing around in a toolbox might be enough to have an effect.

(*)Not counting jets that have been exposed to moisture long enough to turn green.

Addendum: The flow through a jet depends linearly on the Contraction Coefficient, which is 0.62 for a hole with a sharp edge and 0.97 for one with a rounded edge. I put two jets under the metallurgical microscope, one that is a bright color and one that is a dark brown. Both have microscopic roughness around the edge of the orifice of ~15-20 µm and are rounded over a depth and width of ~20-40 µm.

A 1000 nm (1 µm) oxide on brass would be very thick and brown. Any oxidation of the jets would have to be ~20x thicker than that before it would begin to have a geometric effect on the profile of the outlet (like snow on the mountains, the oxide follows the profile of the peaks and valleys. Only if snow were very thick would begin to change the profile of the mountains).


Attached picture Jets.jpg
Posted By: John Healy

Re: Correct needle for 1000-series Concentrics? - 07/10/19 11:41 pm

While a theory it was based on his experience with two strokes that were set aside before AHRMA and the like gave reason to dust them off.
He was asked why would new, jets kept on a jet board, when used in exact conditions they were some years ago lead to consistent seizures.
This was not a random experience with just one racer, but was a reasonable sample. When flowed the results did not match the the number marked on the jet.

When using jets you must remember that over the years there have been many who made jets, some cheeky enough to stamp them Amal. With needle jets
I can identify at least 10 people who make them from around the world including the US. Some like Keyster are brilliant, while others marked will be marked
.106 are .109 and beyond.

If you watch the man flow the jets you will see how little he has to do to move the orifice into size.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 07/11/19 12:11 am

Originally Posted by John Healy
When flowed the results did not match the the number marked on the jet.
To sort this out it looks like time spent measuring jets on the flow bench is in my future. Sigh...
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 07/11/19 9:19 am

No idea if this would be significant but the surface of an oxadized jet should be substantially rougher than the surface of a fresh clean jet.
Remember that oxides grow at different rates according to the orientation of the grain they are growing on
So the oxidised surface should have fingers of oxide poking into the tunnel for different lengths and at different angles.
They only way to prevent this happening would be polish the jet hole to the point where tha oxides fuse to become a semi metallic glass as in the case with polishing for electroplating.

So he could have been right in his observations of a reduced flow in oxadized jets but not for reasons of reduced diameter.

However we might be getting into SEM territory and how one would measure it with out slitting a jet in 1/2 lengthwise is a bit beyond my pay level.
Posted By: Magnetoman

Re: Correct needle for 1000-series Concentrics? - 07/11/19 3:42 pm

Originally Posted by BSA_WM20
So the oxidised surface should have fingers of oxide ...
Except:
Originally Posted by Magnetoman
I put two jets under the metallurgical microscope, ...
I couldn't use the highest magnification/resolution objective because the working distance is less than the recess at the outlet of the jet, but I still could resolve ~1 µm in the eyepiece with the next-highest magnification/resolution objective. If there were any fingers of oxide they were smaller than 1 µm and hence negligible.
Posted By: BSA_WM20

Re: Correct needle for 1000-series Concentrics? - 07/12/19 8:20 am

At what height of roughness dose the roughness of a surface cease to have an effect upon liquids fowing across it, or through it.
Be the sort of thing that would keep a student busy for years.
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