Along with what briggs said...
I would check the cooling system... are all the air channels open and unobstructed, including the blower itself...?
f this only happens after it has been running...
It sounds like you may have an exhaust valve sticking...
If your cooling system is clean and working , switch to a premium, high octane, fuel... that could lower the exhaust valve temp enough to keep it from hanging... :smile:KennyV