RE: How does a gas engine act when hot?
sounds like the engin is getting hot enough to cook the gas out of the carb. Make a little scoop on the bottom of the cowl to vent the air up the front of the engin. Also you could make a disc that fits on the front of the cowl with that size hole, make the two holes larger and rotate the disc so the large holes are open when you fly. when you want scale you rotate the disc back to have the holes the correct size, or have the front of the cowl removeable for flight.It is obvious you have skillz and should be able to modify the cowl to help the heat. At flight time the model does not have to be scale especially if it leads to overheating issues. Not that i fly scale!