Tico,

I think you are spot on with that prop. You are on the right track with the tune up...get back to basics with plugs, wires cap, rotor and timing. Check the timing with a light that has a dial on it. This way you can check your total advance which should be about 32 deg at 3000 RPM. Last but not least..change your water seperator canister and your fuel filter at the carb fuel inlet. A fuel restriction could possibly be your problem.

Thanks Sprink58!