:confused: :confused: :confused: :confused: <br />I have a 1987-195XLC Chapparal fiberglass hull with a OMC-4.3 & OMC-Cobra outdrive..With a 2 barrel Carb .The prop I'm running is a aluminium 15-1/2-15. At full throttle I'm tacking 4800 to 5000 rpm,,but only running about 35 to 38 MPH...