RE: How can you tell if an engine is broken in?
This is a hot topic, everyone has their own ideas about the correct way to do it. The type of piston/cylinder arangement and fit will determine the best break-in procedure. Most sport engines made these days are loose enough to use right out of the box to use without any special treatment. Ringed engines will begin to run better after the first few tanks, ABC engines run good from the beginning. The bennefits of a careful break-in are quickly lost when the plane is flown from a dusty runway.