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Sometimes if your engine is running 100% or close but the rpm is low putting a smaller pitch will do all three, faster out the hole engine rpm and top speed. What is the reason for changing the prop there may be other issues you need to address first before spending the money, is the hull clean and the trim correct. Do a thorough diag of the engine compression, spark, sync, new fuel lines filter and carb rebuild. water pump and thermostat the prop is the last thing not the first!