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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771928
04/24/19 11:26 pm
04/24/19 11:26 pm
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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.


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771931
04/25/19 12:38 am
04/25/19 12:38 am
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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 Files
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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771955
04/25/19 2:35 pm
04/25/19 2:35 pm
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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.


Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771962
04/25/19 5:15 pm
04/25/19 5:15 pm
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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 Files
Concentric14.jpg (370 downloads)
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771967
04/25/19 7:15 pm
04/25/19 7:15 pm
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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.


Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771970
04/25/19 8:10 pm
04/25/19 8:10 pm
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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.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771976
04/25/19 9:11 pm
04/25/19 9:11 pm
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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.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771978
04/25/19 10:04 pm
04/25/19 10:04 pm
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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.

Re: Correct needle for 1000-series Concentrics? [Re: koan58] #771981
04/25/19 10:32 pm
04/25/19 10:32 pm
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Originally Posted by koan58
I sincerely hope that you can pick out the flaw in my calculation.
Sorry, you're on your own.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #771983
04/25/19 10:44 pm
04/25/19 10:44 pm
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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?

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772009
04/26/19 8:57 am
04/26/19 8:57 am
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"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.


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772038
04/26/19 5:35 pm
04/26/19 5:35 pm
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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.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772057
04/26/19 9:33 pm
04/26/19 9:33 pm
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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.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772082
04/27/19 1:24 am
04/27/19 1:24 am
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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.

Attached Files
Concentric17.jpg (265 downloads)
Concentric18.jpg (262 downloads)
Concentric19.jpg (259 downloads)
Concentric20.jpg (258 downloads)
Concentric21.jpg (256 downloads)
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772098
04/27/19 9:22 am
04/27/19 9:22 am
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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.


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772100
04/27/19 9:45 am
04/27/19 9:45 am
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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.

Last edited by gunner; 04/27/19 9:52 am.

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Re: Correct needle for 1000-series Concentrics? [Re: koan58] #772110
04/27/19 1:53 pm
04/27/19 1:53 pm
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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...

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772119
04/27/19 6:43 pm
04/27/19 6:43 pm
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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?



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Oliver Wendell Holmes
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772121
04/27/19 7:42 pm
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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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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772131
04/28/19 2:51 am
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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..

Last edited by Kerry W; 04/28/19 2:52 am.

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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772132
04/28/19 2:53 am
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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...

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Concentric22.jpg (146 downloads)
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772134
04/28/19 4:38 am
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Quote
75 ft.lbs of torque on the screws


Sounds excessive for a carb screw, maybe you meant 7.5ft.lbs?


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Re: Correct needle for 1000-series Concentrics? [Re: gunner] #772140
04/28/19 5:48 am
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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...

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772143
04/28/19 8:53 am
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I'd have suggested an impact driver..


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #772158
04/28/19 2:36 pm
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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

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