Thanks for all the great replys. Still listening if others have ideas.

My Dad and brother and I built many large control line models in the mid to late 60's. We still have a large collection of Cox, McCoy, K&B, Enya, and others. No mufflers, of course, and any open field was fair game for flying. Engines were always started by hand, no matter the size or risk (lots of injuries). That was before those pesky safety, noise, and common sense rules got invented.

The engines of old were temperamental and always required a substantial break-in period. Are break-ins still required?

Also, the model manufacturer recommends a .40 max. Several here are recommending engines in the .40-.50 range. Why?