slows down at high rpms

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  • Fstued
    Senior Member
    • Jan 2014
    • 70

    slows down at high rpms

    This is a problem I have no idea on. As I raise the RPM in neutral they go up in Reverse the engine and prop run faster. Now the problem I go to forward and it runs fine until I start to raise the RPM as I go high the engine and prop runs and turns slower. I am baffled on this one. I'm going to investigate it more today
  • Dave Neptune
    Afourian MVP, Professor Emeritus
    • Jan 2007
    • 5099

    Your description is a bit vague and it seems to point to fuel. It takes very little fuel to "rev" the engine in neutral. However in gear it requires a bit more. In reverse there is a 30% reduction so it will rev much easier than when in forward.

    A fuel pressure gage would be very handy regarding the above. Your problem could be as simple as a clogged filter, failing fuel pump, a loose connection allowing air to be sucked in by the pump or a clogged carb. You have a lot to consider regarding fuel delivery and it could be a matter of the condition of the "tune".

    Take a look at the plugs and report the color. They could be sooty, wet or dry and a light color which would indicate a lean (fuel delivery) condition.

    Have you checked anything? Do you have a primary water separator type filter and a polishing type just in front of the carb? If so check them.

    Dave Neptune