The ABC or ABN engines that do not have a piston ring should not be run in slobbering wet and rich! Without a ring to give a seal, they rely on the piston/liner fit and that has been designed to be correct at the normal operating temperature. When it is cold and the liner has shrunk a bit more than the piston, the piston is too tight in the tapered liner, which is why it is so tight across tdc when new. If you run it really rich, it stays cold and you have a high speed grinder. You need to get it up to near normal temp asap. Not fully leaned out but definitely 2 stroking. After a couple of runs the terrible mechanical tightness across tdc will disappear and all that is left is good compression.

Once I have got mine running, and giving enough thrust and proved that there is some semblance of throttle control, I get it airborne. Then fly it around at a variety of throttle settings. That gives it the proper cooling it is meant to have, the throttle up and down gets it hot and then allows it to cool off a little. It is the heating and cooling cycles that allow the liner and piston to adapt to their new shape (more heat on exhaust side means more expansion on that side).

Engines with a ring whether 2 or 4 stroke should still be run in very rich, though I do get them airborne as soon as they are developing enough thrust.

Harry