RE: Break-in on the ground or in the air?
There have been few engines I didn't like.
The first one was a GHQ. I never did get it to run.
Next was a Rogers 29 with its wipe timer. It ran for about two hours then it was worn out.
And then there was the Pacemaker 59. Beautiful advertisement and it appeared to be well made. I couldn't get it to run for more than a few pops. I sent it back to the factory and they returned it without comment. I finally beat it to death with a hammer.