Elric,
This tapered bore engine should be broken-in according to this method:
http://www.rcuniverse.com/showthread...59&forumid=145
The break-in should be over and done within two, maybe three tanks. When cold, it should retain the "pinch" at TDC
and it is NOT a sign that the engine is not broken-in yet.
If your engine never ran right, you apparently broke it in wrong.
Else, you haven't mastered its adjustment technique.
When you get it back, do it the right way. NEVER run it in, at a four-cycle rich setting. Mind that you don't make it too lean either..