Very controversial subject, I will give you my short and sweet method I developed after owning mroe nitro engines than I can remember though. Crank it, lean it, get it over 200 degrees as quick as possible, put it on the ground, run it, not wide open but don't baby it. Do this for a few minutes, shut it down, BDC the piston, let it cool completely, re fill tank, crank it again. 200 as fast as possible, run it again another 3 minutes or so. I do this about 10 times and call it good, lean it the rest of the way, and its ready to race. The reason I do this is simple, metal expands when it get hot, and wears as it rubs on other metal. Breaking in an engine cold and rich does not allow the sleeve to expand where it will be when its hot therefore there is going to be more wear on the piston liner and the piston if it is broken in cold causing lower compression upon completion and overall shorter life and less performance. I have used the method on everything from Picco .12's to V01B's to RB WS7's and it works great. The other method used on similar motors has shortened life and lowered power significantly. I can say this becuase I am a rebuild freak, my motors get rebuilt completely quite a lot to keep the most power out of them for racing as they don't even come off the shelf just to play with, only for the track. In a couple of gallons I will rebuild a motor so I can tell a difference as the last engine break in was not that long ago.