My Suzuki GS500F  starts from cold first starter push with choke for 30 secs, revs freely to K10 max,  then slowly max revs decreases & dies after 4-5 minutes. Then will not restart until its cold.
Checks so far:- I drained the tank & it's now half full of fresh gas. Fuel filter is clean, fuel taps on reserve, I've stripped, checked, compressed air cleaned jets & rebuilt carbs, checked diaphragms & vacuum tubing, checked tappet clearances & valve timing are correct, spark's good enough to jump an 8mm gap & ignition timing is spot on using a strobe light, engine cut-out works & is in run position.
So to all you fellow newbie bikers out there, any suggestions as to what to do next as I'm lost & NEED help!!!

Is there any chance that the tank-mounted petcock slot is not quite vertical?



If it's open enough to drain slowly, it could still conceivably fill the fuel hose(s) by the time the bike is cold, but not be able to "keep up" when the bike is running.

that is what i was thinking.  there must be a plug in the line that lets a little fuel through.  enough to fire it up but not enough to keep her going