Basil:

Generally speaking, break-in for a ringed engine is moderate rpm, rich, with short bursts at peak rpm, lengthening the high rpm bursts until the engine will hold at peak. The older lapped piston engines were done the same way.

ABC engines, if not kept hot will bind and wear rapidly. They MUST be broken in at a point close to max lean or they stay too cold. Use a fairly small prop and let them wind. Leads to best engine life.

Bill.