Yet another petcock question

[Guest]

Hi all. I have a 83 GS850G that is running pretty well now, thanks to all the help from the GSR forums. The last hiccup is the petcock. I had a problem where the bike would die, but I could get it going again by putting it on Prime. So I replaced the petcock, and did 100 other things, and I had the same problem. I'm running it on prime noow, which doesn't bother me, but I'd like to fix this. Since a new petcock failed, I assume it's not the petcock, but the vacuum. My question: Is it possible that the carb is not producing enough/consistent vacuum to run the petcock valve? What would you do to test/fix this?

I have learned the hard way that OEM is better than non-OEM, the new petcock is not OEM, but fits well. Could that be the problem? I'd rather not spend the $65, hard to believe the new one is faulty. What do you all think?

Thanks for all the help so far. FYI, I have done pretty much all the recommended service in the airbox/carb/fuel system usual recommendations. Nothing electrical tho, except for new battery.

[Nessism]

Pull off the vacuum hose for the petcock and start the engine. If you get a good strong vacuum signal through the hose then you will know vacuum is not the issue.

[Ian Donahue]

Pull off the vacuum hose for the petcock and start the engine. If you get a good strong vacuum signal through the hose then you will know vacuum is not the issue.

Thanks Ed, and thank you for all the previous help. I have done this test (I have been using an external tank and needed to plug the line) and it definitely has *some* vacuum. How strong is a strong vacuum? I have a 20 lb dog, should it be able to suck him up? How would you describe a strong vacuum? Also - where does this vacuum come from? I know - it comes from the internal combustion-ness, but how does that back-track into the carb and up the vacuum line? Is there a passage in the carb somewhere that I should make sure is clear?

[tom203]

Test this new petcock.. Defects can occur. Remove both fuel line and vacuum line from petcock. Then get some tubing thst fits snugly on petcock vac fitting. Sucking lightly on this tubing should cause fuel to flow in petcock's "on" and "res" position. If it flows nicely, then check the vacuum hose itself

when engine is running, the outlet manifold on #2 carb experiences a pressure drop (from atmospheric) due to venturi principle. It's not much but more than enough to move the petcock diaphragm.