I got a 92 ----- my first thoughts when they malfunction after getting hot is an electrical issue , maybe the coil , cdi or alarm box , but it could be a lot of things that could cause it to run bad after waring up , maybe simple as the tank vent is clogged up or turned off and it is not venting the tank and causing a suction that is stopping the flow , maybe the piston/rings are on the way out and after it gets hot the compression drops , maybe a valve sticking after it gets hot
like Goober asked , what does the plug look like ----do you have a compression tester , check the compression cold and then after t gets hot