Brandon is correct. Once the motor is fired, I un-plug the heater. I want to just block the air from the prop and keep the motor warm. If you leave the heater on, you will have to run the engine way rich to keep it cooler. That is too hard on the rod/crankpin.

The only way a motor will break in is to run the motor and try and simulate its "Natural Temps and Enviroment". The piston / sleeve will wear properly as the motor is running, you just want to keep the temps up to keep from having to tight of pinch that makes it harder for the piston to reach TDC. If you run it too rich, that is just as bad as it being cold. I break in with the engine being only a couple hours rich, not blubbering, I also break in half to 3/4 throttle from tank one. 8 plus gallons on every motor I have done.

You'll love the heater.