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Vac Syncing the carbs questions

  • Thread starter Thread starter stng_96
  • Start date Start date
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stng_96

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Hey guys, still working to get my 80 gs1000e running strong. Basically I fix things as my budget has allowed, and I have got it going, but definitely not right. Got the carbs all done like you guys say to(disassembly, soak, new seals, o-rings, etc. I got a new set of intake to head o-rings just because they are cheap, even though mine were not old and worn. Got a good petcock, new plugs.

I just bought a motion pro carb sync tool so I am pretty excited to get it and try it out. My questions are as follows:

I have looked through bassclifs site, and few other places, but I still have not quite found the black and white answer I am looking for. On the service manual on bassclifs site, suzuki uses what looks like a similar tool on the intake runners between the carbs and the head, on that small screw to take the vac readings. In my mind, it should be done at the air jet on the airbox side of the carb, can someone straighten this out for me? Where do I use it?

Also, what should I be looking for as far as readings on the guages? I saw on one site that getting the readings equal is more important then what they actual tell you, but I am not satisfied with that answer.

Finally, last question, when I got the bike, it had caps on the vaccum line from the tank to carb 2, and the guy said he had rode it years ago as is, so I didn't think much of it, what kind of symptons should I expect to see from something like that? I put a new line on obviously, but it has not been run since then so I am just curious.


Thanks guys!
 
is it a stock petcock? Cant see how a stock one would work not hooked to vacuum unless it has been altered in some way. Got pics of it?
 
You wouldn't get any vacuum readings on the airbox side of the throttle plates, as the cylinders can't pull any vacuum there :) The vacuum only exists between the air pump (the cylinders) and the throttle plates. When you do a vacuum sync, what you're doing is adjusting the relative opening of the independent throttle plates to each other. The "breathing capacity" of each cylinder can vary with time, wear, valve adjustments, etc.

So yes, the goal is to get them as equal as possible(*). The absolute vacuum pull is rather irrelevant, and varies quite a bit between bikes. Cylinders breathing equally equates to a smoother idle, which is what you're after. Also carbs badly out of sync can cause other issues. Often to maintain the correct idle speed with out of sync carbs, one of the throttle plates may be too closed, and cause the vacuum to pull too much fuel, causing a rich condition and carbon fouling at idle (ask me how I know...).

You are using the Blue Fluid sync tool? Use caution with that. Don't let the bike stall, don't snap the throttle closed, else you'll pull fluid into the intakes or create bubbles in the risers. Once you've lost fluid in those, they can't really be properly calibrated again without a fluid flush and replacement - not the easiest thing in the world. I'm much happier with the Morgan Carbtune. There should be brass tubes that you put in place of the screws on the intake boots for hooking up the hoses.

(*) - technically on most of the 4-cyl. GS models, Suzuki suggests that cylinders 1 and 4 have slightly higher vacuum than the middle two. Even Suzuki's official tool didn't have absolute vacuum readings, so the difference is a nebulous "half-ball" (see the factory service manual). On the Morgan many people suggest one "line" of relative vacuum, not sure what to do on the Motion Pro smurfy tool, but a forum search may turn something up...
 
I am not sure the petcock is stock, only because it does seem to be in a very poor position to put the tank on and off (fuel line faces directly inward. Ill get a picture this evening and I'll post it up.

Thanks for the info mike, I hate asking questions like this because I consider myself fairly knowledgeable, however I want to get it right.
 
stng_96 said:
On the service manual on bassclifs site, suzuki uses what looks like a similar tool on the intake runners between the carbs and the head, on that small screw to take the vac readings. In my mind, it should be done at the air jet on the airbox side of the carb, can someone straighten this out for me? Where do I use it?

Also, what should I be looking for as far as readings on the guages? I saw on one site that getting the readings equal is more important then what they actual tell you, but I am not satisfied with that answer.

Finally, last question, when I got the bike, it had caps on the vaccum line from the tank to carb 2, and the guy said he had rode it years ago as is, so I didn't think much of it, what kind of symptons should I expect to see from something like that? I put a new line on obviously, but it has not been run since then so I am just curious.
Thanks guys!
Click to expand...

The vacuum tool hooks up to adapters screwed into the holes on the intake runner where those small screws are. Between the carbs and the head. Having them equal across all four cylinders is what you are looking for. The amount of vacuum is irrelevant.
A stock petcock requires vacuum to open. I'd forget about how the bike was when you got it and what the PO told you, and just make sure it's hosed correctly.
 
Ok, so I'll admit I had only talked to friends who used the motion pro before today, and had been happy with it, however after just reading quite a few threads on here, I just cancelled that order and got a Morgan Carbtune on its way. Was only 7 dollars more for the unit itself, and according to you guys, will be a much better piece.
 
I think you'll be happier with that. One thing about the Morgan is that it includes black nylon adapters for the sync ports instead of brass ones. They're usable, but not as easy to work with. The next time you place an order from Z1 I'd suggest getting some of their 5mm brass adapters for use with the Morgan instead.

stng_96 said:
Ok, so I'll admit I had only talked to friends who used the motion pro before today, and had been happy with it, however after just reading quite a few threads on here, I just cancelled that order and got a Morgan Carbtune on its way. Was only 7 dollars more for the unit itself, and according to you guys, will be a much better piece.
Click to expand...
 
Do it with the motor at about 2000, its easier to set them that way
 
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