i have an 1989 50 horse power Force motor that just started overheating recently when i have the throttle down far. when it overheats, an alarm sounds and i shut it off and there is a good amount of smoke coming out the back. the thing that bothers me is that the motor runs fine at an idle speed or going with the throttle half way down. any suggestions? someone told me i might need a new water pump or a new impeller. suggestions???? i idled for about 3 miles with no problem after it overheated today!!