What are the symptoms of a weak fuel pump?

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Turn4fun

Petty Officer 3rd Class
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Jul 25, 2009
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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?
 
F

foodfisher

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Feb 18, 2009
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3,756
Re: What are the symptoms of a weak fuel pump?

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

eurolarva

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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.
 
T

Turn4fun

Petty Officer 3rd Class
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Messages
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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.
 
T

Turn4fun

Petty Officer 3rd Class
Joined
Jul 25, 2009
Messages
76
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.
 
F

foodfisher

Captain
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Messages
3,756
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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