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Topic ClosedEngine Surging at High RPM

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Carolina Blue View Drop Down
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Direct Link To This Post Topic: Engine Surging at High RPM
    Posted: 07/18/2011 at 8:50am

Does anyone know what would cause an engine (90hp Evinrude 2 Stroke) to run okay at low RPM’s (between 1000 & 2000) but when given more throttle the engine will surge. I can run the RPM up to 3500-4500 take my hand off the throttle and the engine will surge Up & Down. It acts just like I was taking the throttle and pushing it forward and back, forward and back. When I throttled back to 2000 RPM it would maintain speed and not surge. I limped back to the dock, made it within 100 yards of the dock and the engine finally stalled and would not crank. I replaced the plugs, two were fouled, two looked okay. Engine fired right up sounded good, I turned the boat around to test it on the open water. I did not get 150 yards away from the dock when it started running rough again, surging and acting like it wanted to foul the new plugs. This time we made it back to the dock…..Called it a day.

Note: The boat ran great the day and night before, so I don’t believe it’s a fuel mixture issue. Thanks for any ideas you may have about this……        
1996 25ft. Crest
90hp Evinrude
Lake Norman, NC
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Direct Link To This Post Posted: 07/18/2011 at 10:09am
It sounds like something is restricting your fuel flow. Check for plugged fuel filter, bad fuel pump, collapsing fuel line, plugged vent on the fuel tank, etc.  When it starts surging on you try squeezing the fuel bulb to operate as a "manual fuel pump". There are several thread on here regarding this subject.
Woody & Marilyn
Covington, LA
Boating in SE Louisiana and
Cedar Creek Lake, TX
Excellent Member of the Month Club 6/09
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Direct Link To This Post Posted: 07/18/2011 at 11:40am
I'll pull the fuel filter and clean it this afternoon. Look around for anything else that might restrict flow. I did notice a heavy fuel smell as well. I'll check for leaking hoses....Question: would a fuel pump slowly go bad or do they tend to just quit working all at once? Just asking because the motor ran so good at lower RPM's? THX
1996 25ft. Crest
90hp Evinrude
Lake Norman, NC
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Direct Link To This Post Posted: 07/18/2011 at 1:34pm
That isn't unusual with a fuel pump. They can supply small volumes of fuel at slow speed but can't keep up at higher speeds.  But check for a leaking hose, sucking air could cause the problem too.
Woody & Marilyn
Covington, LA
Boating in SE Louisiana and
Cedar Creek Lake, TX
Excellent Member of the Month Club 6/09
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