Re: '86 Mercruiser 140 hi RPM Shutdown
could you define "shuts down" better?<br />above 3000 rpm and doing 25-30 mph are you saying the engine shuts completely off to where you slow down, get it back in neutral, and restart the engine?<br />It sounds like an ignition problem, if it were a fuel problem it would sputter but continue running at a lower rpm... usually.<br />A bad plug wire would cause a miss or sputter, and not allow you to reach high rpm, and you would feel it when the engine is under load with the boat getting out of the hole and at higher rpms. If the plug wires are original then probably a good idea to just replace them.<br />With a voltmeter you may be able to compare resistances among the 4 wires, it may give you some idea but I wouldn't get your hopes up that will solve the problem. My best guess is either the condensor or the coil given your symptoms.
