Is this the same motor?
The one on the right I ran a fair bit. I got it from one of the locals at the W/C in Kiev in 1988.
Made a Nelson plug head for it and gained ~1500 RPM. Also made the venturi for it which was about 500 RPM better than the stock one.
Not a power house by any means but always ran smooth and steady. The guy who gave it to me might have put a different P/L in it, not sure.
Leadout in the plane I got it with failed and I never ran the motor again.
The one on the right I think I paid $40 for at a local swap meet. Never ran that one.
Pat MacKenzie