I have a 1993 proline 19 footer center console that is paired with a 1983 Evinrude 140HP. The Motor still has the old 17 pitch OMC prop however it is still in fair shape no chips or warps. Under wide open throttle, the boat sits at 5500 RPM. However, my vacuum speedo says 34 mph, and my GPS says 32 mph. Why is this 140 pushing this boat so slow? I rebuilt the carbs myself when I bought the motor because my needle valve was stuck and flooding the engine. It cant be a fuel issue because of the rpms im turning right? I'm also 100% sure im running on 4 cylinders. As for compression 3 of the cylinders are an even 135 and one cylinder is a little lower at 125 ish. Can 10 psi really slow you down that much? I was told if its within 10 PSI you should still have a good running motor. None of my plugs are fouling, and they are brand new champion plugs as called for by OMC. It had mismatched plugs in it before but I changed those before taking it out on the water. Another thing I ruled out is soaked foam. I pulled my transducer out and it bone bone dry and its on the lowest spot of the hull. Im currently in the process of replacing the deck because the previous owner decided to leave unsealed screw holes in the leaning post. While I have the deck up I checked the foam, its all bone DRY. Thanks.
