I have a 1976 Johnson 75 HP on a 17 ft bow-rider. Using an OMC 14x13 prop, that does not appear cupped, I run 6000 RPM and 29 MPH. I believe the tach is correct, I'm not sure about the speedometer. Switching to a new HUSTLER cupped 13.75x15 prop, I run 5000 RPM and 32 MPH I had expected 5500-5600. I switched props a couple of times and get the same results. I am surprised at the RPM drop. Is this due to the cupping? The engine seems to run well. If I use a cupped 14x13 do you think I'll run in the 5600 RPM range? <br />Thanks again for your continued help.
