ORIGINAL: Rendegade
A 61RF needs more prop than an 11x6. It's a long stroke pattern motor. The hanno's we're running 12x11's if I recall correctly. I think you're under propped and may be putting the plug out to boot.
The best prop for that engine/application is the 11/8 Zinger. That is not a Hanno, and it will not pull the high pitch props.
You better be running 20% castor bean oil in that engine, or it will spit the cylinder liner out the exhaust.
Ask me how I know.
FBD.
