RE: How bad is this engine??
I resumed flying control line when I got out of the USAF in January of 1969. Got married that June and the wife joined me in the hobby. We flew McCoy .40 Redheads and K&B .35 Stallions on our control line models, then, just as the Series 21 made it into the rumor mill, we jumped into flying R/C.
I had messed with R/C a bit while in the USAF (1966), but mostly flew control line because of the financial situation that being in the military brought back then.
I looked at a few Series 21 R/C engines, but never bought one. I was an ardent OS fan back then.
Ed Cregger