SkyDude, I am glad you mentioned both of those engines as they the 2 choices I have narrowed it down to for power in this model. I like the OS61FX I have now, and if the 91FX is as reliable an engine I can't see how it would be a bad choice. EXCEPT, fuel consumption is rediculous on these large 2 strokes. The YS110 is a little pricier than I like, but I have read great reviews on it for power and reliability. Oh the choices we must make in this hobby!