1979 Evinrude 100 HP Intermittant Power Loss

[Frank James]

Model number 100999S, 95% of the time the engine runs fine through all throttle ranges. Engine has very short intermittant loss of power at any throttle position except full throttle (which probably is not noticable). However power loss is a fraction of a second at low speed and has a varying surging at mid throttle or so if left at that throttle position - I do not leave it in that throttle position long as it is very annoying. The engine does not ever die but loses power momentarily. It does not matter if the motor is hot or cold, the sympton can happen at any time. May run fine for three or so hours before the problem occurs or right after the motor is started and run. Stator was defective (battery not charging) and replaced with new Evinrude part. Both Power Packs were replaced with new Evinrude packs. Rectifier was replaced with new evinrude part. Fuel pump was rebuilt (new diaphram). Old diaphram was allright though. On board fuel tank with primer bulb lines were replaced. I also hooked up a 6 gallon tank with new line and primer bulb with no change in performance. Spark plugs were replaced with new ones. Two differennt new deep cycle batteries were tried with same symptons. This same thing happens every time I take the boat out. Operating air temperature has been 75 to 90 degrees.

[Solittle]

Welcome Frank - Two unrelated things come to mind. First is an intermitant air leak somewhere between the tank and the motor. The second thought is some crud in the carbs. Either would result in what you describe.

[Frank James]

Originally posted by SoLittle: Welcome Frank - Two unrelated things come to mind. First is an intermitant air leak somewhere between the tank and the motor. The second thought is some crud in the carbs. Either would result in what you describe.

[Frank James]

Thanks for the advice. The problem turned out to be a defective sensor coil (or lead). I purchased a new sensor coil/timer base and installed it. I have operated the boat 16 hours with no problems. Additionally the engine runs much quiter. Either the sensor coil or a lead was defective.

[Terry H]

Frank...what are you calling the sensor coil? Is that the timer base, located under the flywheel and connected to the throttle? The reason I am asking is that I am having a similar problem with the same model motor.