I have a relatively new (1 year old ) O.S. 91FX on an Ultra Stick .60. I use nothing but O.S. engines and have a pretty good understanding of how they tick. Been in this hobby/addiction for 12+ years. This particular .91 just does'nt seem to have the "UMPH" like my others.(40fx,60fx,46fx,1.60fx) I've tried a rebuild/gasket kit, new o-ring on the carb. and it still is'nt "all that" like I feel it should be. I use 15% Wildcat Fuel the all synthetic blend at 18% oil content per O.S. recomendations.

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