Carb lacks Vaccuum

carbs 1,3 and 4 have good vacuum, when syncing. carb 2 is lower than the rest, can't seem to get them equal.

Okay, so i recently put my bike together this weekend since i tore it down to install new cam chain, bead blast the top end, lap the valves, and adjust valve lash. i took the carb boots off and cleaned them up prior to the blast and re-installation. they aren't cracked, or at least i can't spot any cracks.

when assembling i was able to swap shims around to fix for lash and i checked clearences about a billion times, all within spec. i don't think it's clearances.

The Bike started up nicely when put back together, runs MUCH better, and i wouldn't have noticed if i hadn't check with the vac tool.

i'm going to check compression tomorrow to see whats up with that cylinder.

Is there another way of checking for leaks besides spraying thrust near the boots? i have pods so im not sure the little change in tick over speed was related to a leak.

Maybe, my carbs need cleaning??? Oh, I've got spare boots too.

Post edited by: alberto.f.a, at: 2007/10/28 23:42

Did you "bench-sync" the carbs before reinstalling them? What are you using to check the vacuum? How far off is that one from the rest?

IF the bike where this is occurring is the 78 KZ650, then you have mechanical slides. Either the slide where you have low vacuum is quite a bit higher than the rest or your cylinder isn't pulling vacuum. If you check compression and find you have low vacuum readings, bench sync the carbs. The point of bench sync is to make sure that all four slides are about the same height initially and that they raise and lower in the middle of the adjustment range for the idle screw. If you can't satisfactorily bench sync the carb, it is very possible that the cylinder with low vacuum readings has a defective synchronizing mechanism. I see this frequently; sometimes it can be fixed by stretching the springs inside a tad.

Well, after a couple of hours of poking and prodding i found the problem. The vacuum line to the petcock had a small crack. I replaced and re-synced with success.

Now, I'm going to go for a nice long ride to get my battery all charged up.

Thanks guys.