Pretty generic answer . FAST is what you need - fuel , air, spark, timing . Obviously you are loosing one of those. Most of the time when it runs good cold but acts up when warm, the first place to look is the choke, second would be jetting. This takes only a few moments and some very basic testing. Next would be your ignition system. Each subject is a chapter in a book ( thousands of them out there) More specific question should get a more specific answer