Heat cycle.

Never let the engine just sit and idle during break in. Heat the engine up with a heat gun to about 160+ degrees then start it up. You'll want to run it a little rich the first few tanks, but lean it out enough that the engine will warm up to at least 220 degrees. Run it for a few minutes then shut it off. Be light on the throttle. Put the piston at bottom dead center and let it cool at room temp for at least 15 minutes. Then, start it up again, warm it up to around 220 and run it for another few minutes, shut it off, put the piston at BDC, and let it cool at room temp for another 15 minutes. Just keep repeating the process until you run through minimum 6 tanks of fuel. I like to run closer to a quart. Most people think I put too much time into break in, but the better you break the engine in, the better it will run. You should only have to preheat the engine for the first few startups. It is wise to preheat a new engine since the pinch is so tight.