1981 GS650G vacuum leak and cold pipes..

[Kitten Tooth]

Ok guys, i know i have a vacuum leak but theres another issue that seams to have come up and im not sure if the leak is causing it.. Some of the pipes are cold.. The bike is a 1981 GS650G, i just cleaned the bodies and put new kits in. I havent tuned the pilot circuits yet, i have them set from gently seated to 2 and a half turns out. The bike seams to idle really low and will not start without a spritz of carb cleaner into the airbox. I have spark on all cylinders... I let the bike run for a while to see if it would get better after warming up. It boggs very badly when you try to rev it. If you give it tiny bursts with the throttle it starts to rev up but it does it very slowly and weakly, like its limping up into higher RPMs. I have great compression on all cylinders as well (150 PSI). Any choke at all kills it. I found that it revvs way the hell up if you cover the air box opening with your hand. I also found that if you spray carb cleaner on the manifold boots OR the air intake boots that connect the carbs to the airbox and the motor (doesnt matter which one) it will rev up as well. Pipes coming from cylinders 2 and 4 are warm but when you spit on them or spray some water on them, it just runs down. However, the pipes from cylinders 1 and 3 are totally hot and the water just hisses and jumps off. But, if you spray carb cleaner on cylinder one or three's manifold or air intake boots, it revvs up.. Are my default pilot adjustments way off?? Also, some of the clamps for the carb holder boots are missing screws or just gone completely.. would hose clamps do the job? I really have to get this thing running for this guy, i feel bad for taking so damn long. He isnt mad but this last week has been so nice and i feel like i totally f*&#ed him out of the last few warm days before winter. Any help on this would be very much appreciated.

Thanks guys,
KT

[bwringer]

A vacuum leak that's too small to detect will totally f-up the way a bike runs, so with the leaks you describe, I'm surprised you can get it to start at all. And yes, bad clamps will definitely leak.

So yeah, there's your problem. Or at least one of your problems. You need intake boots, clamps, and o-rings all around.

And I just know you've already checked the valve clearances, right?



Hope you hung on to the old parts from the carbs, too -- you'll need them. The jets and needles in the kits are imitation junk.

[Dave8338]

Intake O-rings between the carb rubbers and the head.


If you've already replace them, as Brian mentioned, check ALL of your clamps. How does the petcock screen look?

[Steve]

Another possibility is CARB SYNC.

Personally, I will set the mixture screws to three full turns out from lightly-seated, then adjust as necessary. I have found that it will run better at idle with a rich mixture than a lean one, especially when cold. After the engine is warmed up (and carb sync done) I will tweak the mixture screws to best idle. They may end up back at 2 or 2.5, but at least it will start easier and run so I can get to the tweaking phase easier.

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