I have a 1992 proline 210 walkaround cuddie with the original mercury engine. Engine starts and runs fine. Accelerates without problems and runs upto 40-50-MPH. Problem starts when I begin to slow down. Engine begins to throttle back but suddenly decelerates rapidly when the throttle is hadly moved. The deceleration is very violent and the boat can go from 40 MPH to 10 MPH in a couple of seconds.