Weird carb sync problem

[Hoomgar]

Sorry if this is a hi-jack Paul but I need to ask a question.

Duane and Einar, what are you two on about here? Aren't his carbs VM like mine? It's a 70's GS so they would be the same right? Were talking about syncing. You adjust the float heights to do that. Each carb has it's own adjustment. What am I missing? What 3 screws are you talking about??? The need to learn is knocking.

Mark, ptm does have 26mm VM carbs.
Einar has CV carbs, different synch procedure.
ptm's carbs have a master carb, #3. It has no adjuster screw for the slide. You set the others to match it.
I'm not sure what you mean by "We're talking about synching, you adjust the float heights to do that". ?? Synching and float adjustments are seperate things.

I meant slides. Sorry about that. So now, why do his vm26 carbs not have an adjustment for the #3 slide? Both my sets do. I wasn't aware there were different animals out there?

[ptm]

I would first check the slide action. If good...
The bike being a "little jerky" coming on and off the throttle could very well be related to that difference in vacuum.
If not the vacuum, then try to determine if this symptom is a rich or lean condition so maybe you can tune it out with the pilot fuel/side air screws.
Does the problem get worse as the bike warms up? Suggests rich condition.
If you temporarily remove the air box lid, does it get worse (lean) or better (rich)?
Also, synching at such low rpm's isn't the way to do it, in my opinion.
I set them at about 3,000/3,500. I'm not saying you must set them there, but at least get the ignition advancer involved and set them at about 2,500? At least this is closer to where you spend time riding.

Thanks, Keith. A lot to think about.

I haven't noticed a difference with the throttle action when cold or hot. Unlike many it is not very cold-blooded, so it runs pretty well from the get go. I think the next rainy weekend I'll just pull the carbs; check the slide action; do a careful bench sync; remount them; adjust the pilot air screws; do a vacuum sync and see what I get. I'll definitely do the sync at a higher engine speed. The manual says 1500, but I've been doing it at the 1000-1200 idle speed (didn't look at the manual and forgot what I had read earlier...). It make sense to do it at higher rpms.

So now, why do his vm26 carbs not have an adjustment for the #3 slide? Both my sets do. I wasn't aware there were different animals out there?

I agree with Hoomgar - I'm a little confused about the #3 carb being non-adjustable. On both the ones on the bike and a set of '79 spares I have, all 4 carbs have the adjustment screw for the slides, including #3.

[Einar J Skog]

Hi

Sorrrrrry for the confusion..

CV carbs have 3 adjusters to sync in pairs .
They are a part of the gas linkage in front of carbs...

Older carbs have 4 adjusters ,on top of each trottle slide.



GS 1000GLx (Yoshimura 4-1,KN filter,DynoJet Stage 1,Wiseco 1100
pistons, Metzeler tires,++++++++++++++++)

[Hoomgar]

Hi

Sorrrrrry for the confusion..

CV carbs have 3 adjusters to sync in pairs .
They are a part of the gas linkage in front of carbs...

Older carbs have 4 adjusters ,on top of each trottle slide.



GS 1000GLx (Yoshimura 4-1,KN filter,DynoJet Stage 1,Wiseco 1100
pistons, Metzeler tires,++++++++++++++++)

Well that's what I figured but not according to Keith now??? He is saying that even the vm266 carbs on this 750 don't have an adjustment for the #3 carb so if that is true I simply want to learn. Why and what models? How do you know?

[KEITH KRAUSE]

Mark, I got caught up reading duaneage's post and because ptm didn't say otherwise in his next post, I assumed his carbs used a master carb. Many people visiting this site have said they have a 750 with no adjuster above the slide at #3. I have yet to see a set of these for myself, but I'm guessing they may be on the '76 or '76 and '77 models??
PS: I just read back and duaneage said "reference carb", not master. However, I've still read about owners saying they have these carbs.

[KEITH KRAUSE]

ptm, good luck with going over things again.
Let us know how the vacuum thing works out, and the other little problem.
If mixture related, the little problem you mentioned SHOULD change somewhat from cold to hot. Cold or hot should magnify any mixture problem, rich or lean.
You can still try removing the lid to see how that effects the problem.
But maybe your re-synch will fix this. Hope so.

[Ghostgs1]

OK, I'm confused. After I balanced my carbs to the same vacuum levels using a Motion Pro mercury manometer, I read the Suzuki GS1000 service manual. Alright, my wife tells me the same thing. The manual says I did it wrong, although the engine seems pretty smooth when compared to my previous bench sync. job. According to Suzuki, #1 & 4 should be the same and 2 & 3 the same, but lower by 1/2 diameter of the steel ball in the Suzuki balancer gauge. Is their any chance Suzuki may know more than I do? Could this be correct? If so, does anyone know what this difference whould be in cm's of mercury? Will this improve performance or is it too small to matter? Thanks for your help again. Confused Ray

[KEITH KRAUSE]

OK, I'm confused. After I balanced my carbs to the same vacuum levels using a Motion Pro mercury manometer, I read the Suzuki GS1000 service manual. Alright, my wife tells me the same thing. The manual says I did it wrong, although the engine seems pretty smooth when compared to my previous bench sync. job. According to Suzuki, #1 & 4 should be the same and 2 & 3 the same, but lower by 1/2 diameter of the steel ball in the Suzuki balancer gauge. Is their any chance Suzuki may know more than I do? Could this be correct? If so, does anyone know what this difference whould be in cm's of mercury? Will this improve performance or is it too small to matter? Thanks for your help again. Confused Ray

I suppose it matters enough or Suzuki wouldn't call for it.
I've never seen the genuine Suzuki tool they picture in the factory manual close enough to see the scale. I would guess "half a ball" would equal 2 cm but could be as little as 1cm?? Hard to imagine anything less would really require a specific procedure? I couldn't tell any performance difference of just 1cm. Not always sure I can tell 2cm either but it does matter to the mixture.
IF YOU HAVE THE STOCK EXHAUST I suggest you follow the factory procedure. If a 4-1 pipe synch them evenly as possible.

[Einar J Skog]

Hi

The outer carbs should be higher by
ca: 2.5 cm (one inch.) of mercury
That is if you have the air filter box and filter..
If you have seperate filters, then you adjust all equally..
It has nothing to do with what kind of exhoust you have...


:roll: :roll: :roll:

[ptm]

ptm, good luck with going over things again.
Let us know how the vacuum thing works out, and the other little problem.
If mixture related, the little problem you mentioned SHOULD change somewhat from cold to hot. Cold or hot should magnify any mixture problem, rich or lean.
You can still try removing the lid to see how that effects the problem.
But maybe your re-synch will fix this. Hope so.

Thanks, Keith. I'll let you know what I find. If it were running poorly, or if the weather was bad, I'd be taking it apart now, but until then, I'd rather be riding every chance I get. There will be plenty of days this winter to dig into it deeper...

[KEITH KRAUSE]

Hi

The outer carbs should be higher by
ca: 2.5 cm (one inch.) of mercury
That is if you have the air filter box and filter..
If you have seperate filters, then you adjust all equally..
It has nothing to do with what kind of exhoust you have...


:roll: :roll: :roll:

Got me scratching my head here. :?
How could the airbox, which is designed to feed each cylinder equally, create the need to set the vacuum higher at 1/4?
I believe that because 2/3, due to exhaust design, has a little more back pressure. This would obviously create the need for less vacuum at 2/3 to compensate. If there's just a little less flowing out, then you need a little less coming in.

[Ghostgs1]

Thanks, Einar & Keith, My settings had been almost exactly backwards after many teardowns and tinkering. I guess that is why it ran so much better when I set them up all the same. Now I am anxious to try it again with the correct info. Suzuki and good folks on GS Resources do seem to know a lot about this. I'll let you know how this progresses. Thanks again, Ray

[Einar J Skog]

Hi

How could the airbox, which is designed to feed each cylinder equally, create the need to set the vacuum higher at 1/4?

Because they do not.
The carbs in the middle got more air.
If you have seperate filters, then all got the same amount of air.
And therefor adjust all equally..

Einar

[KEITH KRAUSE]

Hi

How could the airbox, which is designed to feed each cylinder equally, create the need to set the vacuum higher at 1/4?

Because they do not.
The carbs in the middle got more air.
If you have seperate filters, then all got the same amount of air.
And therefor adjust all equally..

Einar

Every air box I've seen sure looks like it feeds each cylinder equally.
Just a big box that feeds 4 equal sized openings. I can't see or imagine any difference in flow between them.

[Ghostgs1]

Much better now, after correctly balancing the carbs, smoother operating throught the lower and mid ratges. Thanks guys.