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Posted By: aviator79 Slide Cutaway at altitude - 08/13/14 2:31 pm
I have recently rebuilt my 78 T140V. I have also moved to a town at an elevation of 7300 ft, and this is my first go at tuning it for elevation. In the course of the rebuild, I went down a size on the main and pilot jets. I did not replace the slides, as the current #3's have been sleeved by Lund. Unfortunately, now at low throttle openings, the engine stumbles and spits some fuel back through the carbs. I have tried all three needle positions for the needle circuit to no avail. Once I open it up a bit more, it pulls like a champ and sounds great.

So now I'm faced with some options, none of which are cheap.

I can buy new slides, and send the bodies and slides off to to be sleeved. This would cost only a little less than buying new carbs. There's also the possibility that I might go through a couple cutaways before I get it dialed in, which pushes the cost way up since each new slide would have to be sleeved to match the body.

I can buy new carb bodies and slides, but this is also about the same as the cost of new carbs. Trying different slides would be cheapest this way.

I could buy new Amal "Premiere" carbs, which would be a bit more expensive, although I'd get hard-wearing slides and stay-up floats in the deal. Trying different slides would be marginally more expensive than non-premier carbs. I could also surely recover a good bit of the cost by selling the old carbs complete. I'm leaning toward this option.

I have a couple questions:
1) What option would you choose?
2) Does anyone have enough experience with high-altitude running to recommend a cutaway? Is 3.5 enough, or should I be thinking 4? Getting it wrong the first time isn't cheap.
3) Can I get Amal premiers made to order? i.e. Can I get a leaner slide from the get-go or would I have to order the slides separately?
Posted By: L.A.B. Re: Slide Cutaway at altitude - 08/13/14 3:07 pm
Why not simply alter the heights of the cutaways of the slides you already have?

http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter

[Linked Image]

Quote
600 Series P/N 900 Series P/N Stamped as Height of cutaway
622/0602 928/0602 2 1/8" RICH
622/06025 928/06025 2 1/2 5/32"
622/0603 928/0603 3 3/16"
622/06035 928/06035 3 1/2 7/32"
622/0604 928/0604 4 1/4"
622/06045 928/06045 4 1/2 9/32"
622/0605 928/0605 5 5/16" LEAN




Posted By: D.Bachtel Re: Slide Cutaway at altitude - 08/13/14 8:31 pm
How about the next size(s) down on the main jet?
I'd go that route first.


Don in Nipomo
Posted By: aviator79 Re: Slide Cutaway at altitude - 08/13/14 10:31 pm
I already put in 180 mains although the spitting back is waaayyy below where the mains matter. I also did 105 needle jets and tried all clip positions. This spitting is only between just cracked and about 1/4 throttle.

Modifying the slides I have is an option, but I cringe a little too think about my ghetto Dremel machine work.
Posted By: Old Cafe Racer Re: Slide Cutaway at altitude - 08/13/14 11:00 pm
Don't use a dremmel, use a smooth half round file and just take a little at a a time.

davy
Posted By: desco Re: Slide Cutaway at altitude - 08/14/14 9:20 am
Did you do the rebuild before or after the move?
If before, did it run OK at the lower elevation?
I run my bikes regularly at 228' below sea level and at 9624' and above, sometimes with in a week and have had no problems with blow back. They get richer the higher you go. I set them up to run at 4200' at home and don't worry about what happens higher or lower. The only blow back I've had was with the intake valves on the 68 staying open too long with the long duration new cams and I cured that by loosening the valve lash.
All carb settings and specs are by the book.
Start with the easy, cheap stuff.
Posted By: aviator79 Re: Slide Cutaway at altitude - 08/14/14 10:05 am
The rebuild was after the move, and I didn't have it running up here prior to the rebuild.

In reviewing the various guides on tuning Amals, it appears that spitting back is associated with a lean mixture, and not a rich mixture. I has assumed richness just because of the altitude. I wonder if I might have an intake leak or something that's causing a lean condition rather than a rich condition.

I should probably fiddle some more before spending any money.

Desco, I appreciate you sharing the info about riding at 9624. That's the kind of data I need. If it ran right with #3 slides at that altitude, then maybe I'm barking up the wrong tree.
Posted By: kommando Re: Slide Cutaway at altitude - 08/14/14 10:20 am
Richen the pilot setting and see if that makes it better.
Posted By: craig Re: Slide Cutaway at altitude - 08/14/14 6:04 pm
pilot mixture sounds the best idea as what you describe is weak mixture , if the bike does run weak do not file the cutaway as this will make it worse , when at low opening drop the chokes a little , if this cures it then its to weak , try pilots first then reduce the cutaway if needed not incress
Posted By: desco Re: Slide Cutaway at altitude - 08/14/14 8:15 pm
http://victorylibrary.com/CONC.htm

The Amal Bible, and a good read on a long winters night.
Posted By: aviator79 Re: Slide Cutaway at altitude - 08/14/14 10:46 pm
I richened up the pilot circuit and it runs very much better. I can blip the throttle now and get a crisp smooth pickup off idle. It seems strange though, the pilot screws are only ~1/2 turn out. At this altitude it doesn't seem like they should run so rich. Intake leak perhaps?
Posted By: desco Re: Slide Cutaway at altitude - 08/14/14 11:01 pm
You are going to have to figure that out for your self.
Trying to fix one of these old turds on the internet is like trying to remove your own appendix over the phone.
Posted By: Pete R - R.I.P. Re: Slide Cutaway at altitude - 08/15/14 1:19 am
The mixture screw would normally be about 1.5 turns for best running. The pilot jets could need cleaning with a 0.016" diameter wire or number 78 drill bit.
If that's not it, check that the float bowl surfaces are flat and not leaking air at the bowl gasket.

It could also be blocked idle discharge holes, near the front lower edge of the slides (2 holes in each carb).
Posted By: Nick Re: Slide Cutaway at altitude - 08/15/14 1:54 am
Since it's going to run richer at higher altitude, if it is the slide causing your problems (which I doubt it is) all you have to do is file the cutaway a bit higher, a half-miillmeter at a time.

Spitback = lean, no?

Better make sure those pilot circuits, and everything else about those carbies, is correct first.
Posted By: triton thrasher Re: Slide Cutaway at altitude - 08/15/14 5:13 am
Originally Posted by aviator79
. I wonder if I might have an intake leak


Test for an air leak and wonder no more.

With the engine idling, spray the joints in the inlet system with WD40 or similar.
Posted By: craig Re: Slide Cutaway at altitude - 08/15/14 9:20 am
nick heres some reading for you
http://matchless.rhobbs.co.uk/downl...icing_-_Issue_33_-_Classic_Mechanics.pdf
Posted By: triton thrasher Re: Slide Cutaway at altitude - 08/15/14 10:11 am
Originally Posted by craig


They've mislabelled their drawings of Monobloc and Concentric!
Posted By: 750 Tracker Re: Slide Cutaway at altitude - 08/15/14 11:31 am
It appears you have enough suggestions, so I won't add to them.
But, the first rule of any tuning process is to only change one thing at a time. Good luck.
Posted By: John Healy Re: Slide Cutaway at altitude - 08/15/14 11:55 am
Because all of the fuel is metered at these lower throttle positions in the Main carburetor by the diameter of the needle jet it is where your most of your concern should be. It is also the throttle opening where the Idle carburetor has the most influence upon the overall mixture. The needle clip adjustments or changes to the main jet (except in situations where a mistake is made and one that is much too small is fitted) have no effect at these low throttle openings.

The variations available with the numerous slide cutaways allow one to change the vacuum signal on both the idle circuit and the main carburetor at these lower throttle openings. The idle carburetor is important to get right as when you raise the slide the secondary idle carburetor transfer (the larger of the two transfer ports and located under the slide) changes how it works. When the slide is down it acts like an air feed mixing with the fuel in the mixing chamber below. Once you open the slide, the vacuum signal equalizes between the two transfer ports and the secondary port now starts to deliver fuel. When all is right with the carburetor very few changes need to be made to the idle main jet (aka pilot jet) at higher altitudes other than turning out the pilot air screw a bit.

Now you say you installed a .105" needle jet, which is what all of my customers in the Denver area are using, but you are still experiencing problems. I would measure the inside diameter of the jet to confirm its size. There are over 10 people making needle jets and some are less that accurately made. There are even people stamping Amal on there products. So it is a bit of a consumer nightmare. When experiencing problems of these carburetors you have to get back to basics. And this starts with an Amal carburetor is measuring the needle jet to confirm size. Using a .105 minus (.1048") measuring standard check the jet. The standard should be a snug fit. A .105" nominal would be a light finger press fit. Next I would verify the float level. If it is too high the overall fuel mixture will be rich., if too low it would be lean.
HTH

Posted By: old mule Re: Slide Cutaway at altitude - 08/17/14 5:21 pm
What is your carb setup for 4900 feet? My T140V and I live at 4400 and am about to rebuild my Concentrics.
I'd sure appreciate a run down of your settings.

Thanks
Posted By: desco Re: Slide Cutaway at altitude - 08/17/14 5:35 pm
John,
Where does one obtain these precision measuring devices so often referred to on this sight and where also do you obtain;
1) The knowledge that they even exist.
2) The skill to use them.
3) The knowledge of when and where to use them.
Is there a book??
I've been wrenching on these old turds for more than thirty years and there are times I don't know what the real mechanics on this sight are talking about.
My collection of precision tools contains a variety of hammers and various grades of Emory cloth.
Thanks.
Posted By: Old Cafe Racer Re: Slide Cutaway at altitude - 08/17/14 7:55 pm
And just to complicate matters further, I recently found to my dismay that although Wassell and Amal throttle slides are completely interchangeable, my new Amal #2.5 slides have the same cutaway as the #3 Wassel slides I was replacing to richen things up down low frown
It's confusing out there sometimes and I'm glad I have engineering experience and good range of tools to navigate my way through the modern jungle.

davy
Posted By: desco Re: Slide Cutaway at altitude - 08/17/14 8:51 pm
http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

To Old Mule,
I never wrote down any info on the carbs it's whatever they come with I think. I did have them bored and sleeved, even the brand new ones just to avoid a hassle later on. They stay set for years except for cable stretch. I clean the pilot jet and ports every spring or so.
Between the carbs and the EI, maintenance is down to valve adjustments, oil changes and keeping an eye and ear open for changes.
Things do wear out or break but points, timing and carbs are things I do not think about.
What I do remember; clip is in the middle, 3 1/2 slide.
One set has the chokes, one does not. Can't tell the difference, don't use a choke anyway. Good luck.
Posted By: John Healy Re: Slide Cutaway at altitude - 08/17/14 9:03 pm
Quote
Where does one obtain these precision measuring devices so often referred to on this sight and where also do you obtain;
1) The knowledge that they even exist.
2) The skill to use them.
3) The knowledge of when and where to use them.
Is there a book??
I've been wrenching on these old turds for more than thirty years and there are times I don't know what the real mechanics on this sight are talking about.
My collection of precision tools contains a variety of hammers and various grades of Emory cloth.


1. Plug gages are available from any one of a number of distributors that serve the machinist trade. I use Travers Tools, but people like MSC also carry them. For our dealers convenience we carry a stock of them. You are looking for a .105 minus (.1048"). They cost less than $10.00.
2. In a perfect world They should fit the jet with a slight drag.
3. I know that I have been doing seminars on all this stuff for nearly 20 years, written about it in Vintage Bike, and talked by self Blue in the Face on this web site. If you remember I had "It's the needle jet stooped" where the Carlin quote is now. Yes there is also a booklet that I have passed out at the seminars.

As far as when to use them - I check every needle jet before I put it in a carburetor. I wouldn't put an Amal on a motorcycle without without checking the needle jet !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If I have said it once, I have said it a million times (a quote from dear old mom) there are more than 10 manufacturers of needle jets. Most don't have a clue. The measurements are all over the place. I had a dealer return a Concentric that the customer couldn't get to work. While the carburetor sat on the dealers shelf he stole the original needle jet out of it to help out a customer. He replaced it with one he got from an independent manufacturer in the mid-west. Clearly marked 106 but the biggest plug gauge I had at hand was .109" and it fell through the jet.

MOST OF THE RIDING WE DO IS ON THE NEEDLE JET. The straight part of the needle doesn't clear the needle jet until about 1/3rd throttle. The needle is .0985" in diameter. So that leaves an orifice with .0055" clearance. That is less than the diameter of most human hairs. Raising and lowering the needle clip does nothing at 1/4 throttle. Thus the T-shirt we have with a needle jet and the saying: It's the needle jet stuupid.
Posted By: craig Re: Slide Cutaway at altitude - 08/18/14 3:02 am
amals are simple in comparison to SUs , but if you want the best running triumph you will ever ride fit a SU
Posted By: Hillbilly bike Re: Slide Cutaway at altitude - 08/18/14 6:20 am
Originally Posted by desco
John,
Where does one obtain these precision measuring devices so often referred to on this site


I'm a hillbilly...#36 drill bit is .1065 and maybe two bucks. Cheap drills may vary a bit in size...so use your micrometer on the shank end...to get rid of the 1/2 thousand, pointy end first in a drill,polish with #220 abrasive,measure with your micrometer.
Posted By: John Healy Re: Slide Cutaway at altitude - 08/18/14 8:38 am
I'm one of those Yankees who still has the dollar my father gave me in 1966 when I opened my first store. I will drive a car until the doors fall off and my family takes it away from me. My wife is embarrassed to give my old shirts to the homeless. But I would skip lunch for a week to have a set of accurate plug gages to measure needle jets, etc.

Even here at "John's Pretty Good Motorcycle Shop" we try to have the right tools to do the job.

In reality you need two for each size: a plus and a minus. This gives you a go-no-go pair.

Besides Hillbilly he needs a .105", not a .106".
Posted By: Richrd Re: Slide Cutaway at altitude - 08/18/14 9:18 am
I once had to check 5 new 106 jets to get a pair that were the right size.
Posted By: craig Re: Slide Cutaway at altitude - 08/18/14 10:05 am
or forget the gauges and just measure the flow rate for each jet to get a matched pair , i use parafin and a stop watch , sounds crude but i find it works
Posted By: Hillbilly bike Re: Slide Cutaway at altitude - 08/18/14 11:20 am
Originally Posted by John Healy
I'm one of those Yankees who still has the dollar my father gave me in 1966 when I opened my first store. I will drive a car until the doors fall off and my family takes it away from me. My wife is embarrassed to give my old shirts to the homeless. But I would skip lunch for a week to have a set of accurate plug gages to measure needle jets, etc.

Even here at "John's Pretty Good Motorcycle Shop" we try to have the right tools to do the job.

In reality you need two for each size: a plus and a minus. This gives you a go-no-go pair.

Besides Hillbilly he needs a .105", not a .106".


I got $20 that says you can accurately gauge a jet using a hand "sized" drill bit grin

The right tools? Sometimes the right tool is any tool that'll do the job without pain..
My LSR Triumph ran 124.9 and a 125.00 mph on the second run on a warm humid day.I do believe this is the fastest official speed of a naked stock swingarm frame 650 Triumph in recent history in a standing start competition. I'm a retired construction electrician not a pro mechanic.. The piston valve clearance reliefs were done my me with a hand held Dremel tool,The valve lash has never seen a feeler gauge,the timing is adjusted by without a strobe light. But it has been on a dyno several times to tune for the best power....
All the tools have little use if the person using them has no "feel" for the job at hand.
But...I took your advice and just bought a .106 go and no go gauges,7 bucks for both... :bigt
Posted By: craig Re: Slide Cutaway at altitude - 08/18/14 11:37 am
sounds good to me , what fuel did you run ?[Linked Image]
Posted By: Magnetoman Re: Slide Cutaway at altitude - 08/18/14 11:52 am
Originally Posted by Hillbilly bike
I got $20 that says you can accurately gauge a jet using a hand "sized" drill bit
I've got $20 that says that while some people can, many people can not. Wear of only 0.0005" of the needle jet is enough to seriously upset the mixture, so what is required is a calibration standard -- either purchased or home made -- that is accurate to no worse than 0.0002". Making a measurement to an absolute accuracy of a few tenths with a micrometer is by no means trivial. Even if someone has a digital micrometer that has a resolution of tenths, that does not mean it is accurate to tenths. And, even if a micrometer is calibrated to an absolute standard by one person, that does not mean when the spindle is cranked down by a different they will get the same result to within tenths. Commercial plug gages eliminate all that.
Posted By: John Healy Re: Slide Cutaway at altitude - 08/18/14 1:26 pm
Quote
My LSR Triumph ran 124.9 and a 125.00 mph


As we are only interested in under 1/3rd throttle what you do on the main jet, while impressive, has nothing to do with the conversation. wink

This thread started with a problem at low throttle openings. As the needle jet is one of the underlying foundations of fuel delivery at these throttle openings we must keep the discussion on the parts of the carburetor that are in play. The needle jet is a main player and the only part in the carburetor subject to wear.

Have you had your micrometer checked for accuracy in the past 30 days? Did you have it done professionally with a standard that can be traced back to the Bureau of Standards? The people at Vermont Gauge do. Do you make sure the part to be measured is the same temperature as the instrument you are using. When you are measuring to tenths this matters.
Posted By: Magnetoman Re: Slide Cutaway at altitude - 08/18/14 2:22 pm
Originally Posted by John Healy
Have you had your micrometer checked for accuracy in the past 30 days? Did you have it done professionally with a standard that can be traced back to the Bureau of Standards?
It's even more difficult than that. Even if your micrometer reads 0.0000" when the anvils are in contact and 1.0000" with a 1" calibration standard, that doesn't mean it will read, say, 0.1050" accurately. The 0" and 1" tests confirm the frame hasn't been sprung open or closed, which is a good test to do but it isn't sufficient.

Even if a micrometer were perfect when new, if it spent time in a production environment measuring parts of a specific size (i.e. with a specific angle of rotation of the spindle) there could be uneven wear of the threads. This isn't a hypothetical problem. My "Brown & Sharpe Micrometer Calibration Standards Set" contains 12 pieces (including, coincidentally, a 0.1050" gage block) to check the calibration with the spindle at 0, 90, 180, and 270 degrees.

As John wrote, for this application tenths matter. When dealing with needles and needle jets one needs to make measurements to an absolute accuracy of tenths, and having a micrometer with this resolution isn't nearly sufficient. Even with an accurate set of gage blocks and a good quality micrometer, making measurements that truly are accurate to tenths is by no means trivial.
Posted By: Hillbilly bike Re: Slide Cutaway at altitude - 08/18/14 6:40 pm
Originally Posted by Magnetoman
Originally Posted by Hillbilly bike
I got $20 that says you can accurately gauge a jet using a hand "sized" drill bit
I've got $20 that says that while some people can, many people can not. Wear of only 0.0005" of the needle jet is enough to seriously upset the mixture.


I was making reference to JH... wink Maybe .0005 wear on the jet needle is not such a bad thing with the usual E10 gasoline causing a slight lean condition on some engines. Non ethanol gas is sold around here and it does fuel better in marginal situations.
Posted By: John Healy Re: Slide Cutaway at altitude - 08/18/14 7:20 pm
HB, if anything these Amal's are already rich these days with what was stock jetting.

They run even richer if the slide clearance is reduced when the carb is sleeved. Most people who sleeve these carbs have learned this and use the standard .004" + slide clearance. This is the clearance the stock jetting is based upon!!
Posted By: Hillbilly bike Re: Slide Cutaway at altitude - 08/18/14 7:53 pm
Originally Posted by John Healy
HB, if anything these Amal's are already rich these days with what was stock jetting.



What is reason? E10 fuel has a slightly lower stoichiometric point than non ethanol gasoline so it's going to be a tad leaner if all else is the equal.
Posted By: Magnetoman Re: Slide Cutaway at altitude - 08/18/14 9:02 pm
Originally Posted by Hillbilly bike
...if all else is the equal.
Unfortunately, it's not. The flow volume through a given jet depend on fuel density and viscosity. Both of these differ significantly for different fuels at a given temperature and their temperature dependence differs as well. Besides, this is on top of John's point that without a precision measurement you don't know if your needle jet is too small or too large to begin with.
Posted By: John Healy Re: Slide Cutaway at altitude - 08/18/14 10:17 pm
Quote
E10 fuel has a slightly lower stoichiometric point than non ethanol gasoline so it's going to be a tad leaner if all else is the equal.


Which with my experience with Amal's that only get richer at lower throttle openings due to wear of the needle jet, is a GOOD thing, not bad. Now some will jump in here and mention slide wear compensating, but if the carb isn't over tightened slide wear is not an over riding factor.

Whether you choose to believe it or not just because Amal is stamped on a needle jet does not prove that it was it made by Amal... That's just a fact. If someone wants to stop by I will be glad to show you some. Just because 106 is stamped on the jet does not mean that it measure .106", that is just a sad fact.

When you make a change, and you don't get the results you expect, it is time to go one step farther and ask some questions. In this case, with the history of poorly made and calibrated needle jets that are actually more available than the original Amal ones it is IMHO time to start measuring. Unlike the main jet that is calibrated by flowing on a manometer calibrated by a standard the needle jet is calibrated by size.

This is what started this thread. A change was made that is commonly done by people who live at 5,000 feet and above and the expected result was obtained.
Posted By: Hillbilly bike Re: Slide Cutaway at altitude - 08/19/14 7:20 am
Originally Posted by NickL
I think fuel density/specific gravity has an input with jetting as well as e-content.
There were a few tests done with 98 octane over in the uk some years ago and some manufacturers of'super' 98 were slated as it's ok with compensating engine management but hopeless with carburation,
temperature compensation is one factor. I tend to stick with BP 98 as it was always the benchmark fuel in the tests. Although i'm probably well out of date now.


I'm aware of specific gravity from the VP fuel used in my race bike. Once the bike is jetted properly a change in SG will affect the A/F ratio. During the race meets many guys cover the fuel tank to keep fuel temperature constant.
On the street with pump fuel you have no idea what's coming out of the dispenser nozzle.The alcohol content varies,water in the fuel affect the A/F ratio. Ethanol absorbs water and the very slight water present in storage tanks can cause the ethanol to drop out of the gasoline. Since the ethanol is a octane booster/oxygenater you now have a different fuel... Any attempt at jetting is going to be a compromise...
And my bike might be the same spec as your but that doesn't always mean your jetting is the best for mine...But I'm not saying accurately checking jets sizes isn't important...it is

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