I've got an 82 XJ750 Max.... I all the sudden the other day the bike started to missfire (not terrible, but quite presistant and severe at times... seems to occur more at full throttle.) Then, today, I noticed that the petcock was squirting small dropplets of fuel out of the side in what appears to be a tiny vent-hole (or is it a crack?) on the rear side. It doesnt leak much, but I notice the small dropplets of fuel leaking off every now and again. Could I have a problem with the petcock? Maybe theres a problem... causing the carbs to be starved for fuel... causing the missfire. Maybe the two aren't related at all. I'm not entirely sure. Any ideas? I guess I'll end up pulling it off to see whats the matter.

Sounds like you need to rebuild your petcock. When the engine is low on fuel, however, it doesn't cause misfire. Sounds like you need to resync your carbs and check your mixtures.

Alright... gona get a 5-gallon bucket to drain off the fuel tomorrow. I pulled my spark plugs out today... cyls. 1, 2, and 3 were fairly normal (greyish white)... but cyl # 4 was black. That indicates too rich of a mixture on the #4 carb. I think the thing to do here is to start over with the carbs... I'll pull them out and clean them top to bottom.

Are you getting reasonable miles per gallon? A while ago, my bike started running terrible. Ran rich and went through a tank of gas in 40 miles. Three plugs were fine, but the fourth was all black. So I took off the floatbowl on that carb and found the main jet sitting in the bottom of the floatbowl. Hope your problem is as easy as mine.

first is it the org. pitcock? if so then the diaphram could be bad in the pitcock. when it goes bad gravity feeds your bike instead of the mini fuel pump in your pitcock. as you increase throttle there is a need for more fuel which you arent getting if the diaphram is bad. hence the backfire and sputtering. i had the same problem with mine but i jus got a new pitcock from dealer for $83.00. i think you can get the rebuild for like $18.00. but at 20 plus years old i went with a new one.
good luck. and rember even a little gas leak is a very bad leak. <_<