My 1995 Malibu Sunsetter with a 350 Tournament Ski engine will start and run well but after stopping for over 20-30 minutes it will start up again but only run for a couple of minutes before dying. It seems to take 20-30 minutes to cool down then it will start again. Am I developing vapor lock and how do I fix this. Has been going on for several years. Engine has less than 500 hrs. on it.