Ok I have a 93 f2 that I bought recently that did not run and had oversize jets in it. I replaced them with the original size jets, cleaned the carbs, changed the oil, plugs, the works. I had it running great after re-syncing the carbs. Had zero problems until one afternoon the bike was sitting in the yard and just felt over on the clutch side of the bike, as soon as I noticed it had fell I picked it up and moved it to a better location. Next morning I go to ride and it just pours gas from the exhaust so I drain the carbs clean them again and the oil and so on so I don't risk hydrolock. I turn the gas on and after a minute it starts to over flow the carbs. I have gone over the tank and the carbs several times but to no avail. The petcock is vacuum operated but when I turn it to primary or reserve it acts like a gravity fed petcock. So long story short would a bad diaphragm for the petcock cause my issue of overflow if everything else is OK with the bike? And just just to be clear I did not have this problem prior to it falling over.