I just purchased a new/old OS .91fsr that came across the RCU classifieds, what a beauty and a beast, it is the size of a 120AX, maybe a little larger. Have any of you run one of these before? What would be a good size prop to try? This engine has a large carb, large cylinder ports and passages, large everything. From the looks of it, I would expect it to breathe and rev better than a .91fx maybe with smaller props? Anyone know?

Does anyone know what was changed with the .90fsr (circa 1979) to prompt OS to introduce the .91fsr (1985) a few years later? I am curious, can't find much info on these engines.



Mike