1995 maristar wont start when hot

[gr82bgreen]

Hi guys. First post. Just bought a 1995 maristar 200 vrs. 350 tbi 275. Took it for a test drive. ran great. shut it off after 5 minute drive. I t would not start. it would crank normally (plenty fast enough to start it). checked tbi, it was spraying fuel. checked spark at coil, ok. waited 10 minutes and it started right up. drove for another 20 minutes and it ran perfect. shut it off and would not start again. got it home and it started right away. P/S, I filled the tank with 85 octane reg. Does it need premium. Any help is apreciated. thanks, Lorne