Interestingly enough, the instructions included in my new O.S. 21 VG, say SPECIFICALLY, don't idle tanks through it for break in, or ever for that matter. The motor never gets up to operating temps, the componants don't expand enough, and the running actually causes excessive wear. Best way to break a motor in, is get it started, and drive it around very rich, getting it to at least 220. I've broken in plenty of motors, airplanes, cars, ect... I do the same thing every time. I put the motor under the operatiing conditions they will be used in.