ok, just to clarify my question, before I go out and rebuild the petcock..
if I apply a vacuum to the petcock, will the petcock HOLD the vacuum, or does it have an orifice or something built into it to prevent it from staying open due to vacuum. In other words, does it have a small leak in it by desigN?
reason I am asking, is occasionally my bike acts like its starving for fuel.. most notably when its cold, although it has happened when warm. In fact I was suffering from it this morning, then all at once, like flipping a switch, there was gobs of power avail. I understand it may be carb related, but when I cleaned the carbs just a few weeks ago, I noticed if I pulled a vac on the petcock, it did NOT hold it at all.
as far as mods and such, just ear shave, stock jets, no shims, stock exhaust. filters are UNI pods. I believe I have the mixture screws about 2.5 or 3 turns out.
oh, a plug check showed them about as clean as when new... very little signs of any deposits at all... I have not changed plugs since I owned the bike, so that would make them at least 1 yr old