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  1. #1
    Seaman
    Join Date
    Jul 2009
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    51

    Default What are the symptoms of a weak fuel pump?

    How do I tell if my fuel pump diaphragm needs to be replaced? Early 70's 55hp magneto ignition, single carb.

    If the pump is in good enough shape to start and idle smooth and run in the lower ranges fine but is not good enough for WOT running, how will it act? Would I expect it to just have a significant lack of power at WOT or should it be sputtering and missing?

  2. #2
    Captain
    Join Date
    Feb 2009
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    Chula Vista, Ca.
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    Default Re: What are the symptoms of a weak fuel pump?

    Just like a heart, a weak pump can't keep up.

  3. #3
    Rear Admiral eurolarva's Avatar
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    Jun 2003
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    Minnesocold
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    Default Re: What are the symptoms of a weak fuel pump?

    If it is original replace it. The diaphragm is only about 5 bucks and it only takes about a half hour to do it.

  4. #4
    Seaman
    Join Date
    Jul 2009
    Posts
    51

    Default Re: What are the symptoms of a weak fuel pump?

    I have no idea if it's original or not. I'm replacing it regardless, just trying to determine if a weak pump is causing my top end power loss problems or something else. It's the only thing I haven't been able to rule out yet but my thoughts are that a weak pump would just cause the carb bowl to be sucked dry at WOT and it would start sputtering. I don't have the typical starving symptoms, but acceleration just hits a brick wall above 3/4 throttle.

    BTW, where do you get one for $5 at, the cheapest I can find is like 17 bucks.

  5. #5
    Captain
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    Default Re: What are the symptoms of a weak fuel pump?

    My next check would be timing.

  6. #6
    Seaman
    Join Date
    Jul 2009
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    51

    Default Re: What are the symptoms of a weak fuel pump?

    Timing is correct, throttle sync is correct, all ignition components good, points gapped and sync'd properly, no bad wiring.

  7. #7
    Captain
    Join Date
    Feb 2009
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    Default Re: What are the symptoms of a weak fuel pump?

    If everything is correct, maybe you are expecting too much out of the motor. If the RPM's are there, the load may be too heavy, the prop may be the wrong pitch. Sorry, I'm out of suggestions. Maybe Frank will chime in.

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