I'm thinking running hot. I had a guy kept calling me about how it wouldn't start when it was hot and it turned out he had the thing running at like 250-270 degrees, since they have plastic carbs he wasn't getting boil off at the carb but when he tried to start it after stopping it wouldn't start because the fuel was actually boil off when it hit the crank shaft below the carb and since it wasn't running there wasn't enough flow to keep it running like it was so the fuel boiled off.