Neighbor Proffessor has problem with Craftsman rider. 15.5 Briggs vertical shaft

Mt neighbor, Math Professor, has a Craftsman rider with Briggs 15.5 HP vertical shaft engine. I will hear him mowing and the mower runs great until it gets warm/hot and suddenly quits. Let it sit for for awhile and uses his push mower. Rider will start again after about 30 minutes. Runs fine for awhile and then quits.
I try helping him at times, plug is fine, gas fresh and clean. I have adjusted the carb for him. Anyone have a suggestion. The neighbor is a Doctor of Math here at Tarleton State University in Stephenville TX. Trying to help him out.
Any suggestion will be appreciated.

Thanks in advance
Rec Cox

Adjust the valves, would be the next step...

I have been the drinking buddies of many proffessors, the adjustment is free and easy. Just tell them that the valves expand with heat, and need to be checked from time to time.....

Try a new fuel filter. gregjo1948

Check for spark as soon as it shuts off.
Sounds like a coil going bad.
Also check the gas cap vent hole.