I apologize in advance if this question has been answered elsewhere but the symptoms don't allow a proper keyword search. I have an '88 25 HP Evinrude manual start, has always started and run fine. Friends borrowed the boat, described a problem where advancing the throttle past a certain point brought on terrific "hunting" which lasted until the throttle was turned back to low. Two weeks later I put in fresh fuel, had no problems for two 30-minute runs, figured problem was taken care of. After three hours of cooling, got back in the boat and the problem they spoke of reoccurred. I read about the S.L.O.W. system and thought maybe it was an overheating issue, but there's plenty of water coming out of the water pump indicator and I heard no warning horn which I've read sounds when the S.L.O.W. system is activated. My friends said they were able to get a little more rpm with the engine cover off, which I also found to be true. So my question is...is it possible for the S.L.O.W. system to kick in without a warning horn? Faulty thermostat, perhaps? Since the problem is only when attempting higher rpm, should I be looking at the fuel delivery side instead? It's quite amazing how it runs steady at hull speed but a slight attempt to advance the throttle means it cuts out a little and more throttle means more cutting out. Any advice would be greatly appreciated.
