If some of you guys could help me with this little test, I would appreciate it. I am trying to track down my inconsistent idle problems. Trying to figure out if it's the petcock. I sucked on the vac line, but nothing comes out as it should. However I have problems with the idle. Let's say first stop at traffic light it idles normal around 1,200. Drive off to second, idle could be at 1,500. Drive off to third traffic light, it about dies. Drive off again idle could be around 1,000. Drive off again idle is normal. This goes on all the time, not necessarily in that particular order, but it does it only when warmed up. So I keep messing with the mixture screw, needing it to turn it more lean, but will get more of a flat spot at about 1/4 throttle. It needs to be a 2 1/4 turn to run good, but idles crappy. Turn it to 2 turns out idles better, but has that flat spot. I haven't changed the setup in a year, and last year it ran perfect like this. Now that I have to go leaner, it could mean that the petcock might have a tiny leak, so a little gas gets through the vac line into the carb, thus messing up the setup.

Now my question is if some of you guys could try what I did:
While idling, pinch the vac line where it curves up near the speedo cable and see if the idle goes up about 100-200rpm and the idle gets more stable on mine then too. IMHO it shouldn't make a difference to the idle doing that. I wanna make sure it's the petcock for sure before I buy a new one.

Thanks for any input.

make sure that the vac line is securely clamped at both ends and not cracked... this would cause an intake leak...
if not that,... my guess would be a sticky slide in the carb,... go in from the top of the carb, pull the slide out and clean off residue from the slide and the cylinder....

Raftguy,

Just for you, I took a little ride to warm it up to a perfect idle, then I pinched the vacum line,.......and I cannot detect any difference in idle when the line is pinched. But I notice you sure can feel the pulsing of that piston thumping away, when squeezing that hose.

IMO, if the hose is good and clamped tight at both ends, and the diaphram is not leaking, there will be no difference.

But seems like if you were to disconnect the hose from the diaphram, and block it, then run on prime, that would eliminate any problem in that circuit. If you still have the problem, and you are sure there are no other vacum leaks, then its time to attack the carb.

You can check for vacum leaks by spraying wd-40 around the carb intake area, and note any RPM change.

Is there any chance you have a valve too tight ? But if it runs good above an idle,....not likely I guess.