I have a 1984 Bayliner capri cuddy 19.5 ft,4 cylinder volvo penta inboard,I think it is an AQ 125.270 outdrive with a prop that is 14D 17MWC (aluminum).It runs great and I have checked the compression on all cylinders and they are all at 150 PSI.I only get 18 MPH at 3800RPM with a light load.If...