I would follow the manufactures recommendation on break in.. I always do it with the engine on the plane. The process usually involves running it very rich to the point where it is 4 stroking for about three minutes, then idling, then running up again but leaner.. I usually run the motor for about 2 tanks worth like that before leaning it out to peak. even then I will back up just a click rich. Still.. it is best to do exactly what the booklet that came with your motor say's. good luck,

FW