RE: Evolution 1.00 vs OS 91 FX
The 91FX is a nice running engine with good power/weight. People often complain when they will not swing an 18" prop very well or when it goes lean with the tank mounted 18" from the engine. It has a big carb that does not pull fuel very well unless the rpm is way up, and it needs a pipe for good power with the larger props. In fact a piped 60 is simply more powerful than any muffled 90. The most powerful and consistant running 91FXs I have seen are using a pump and a pipe.