Mechanical fuel pump going bad?

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Hendog458
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Mechanical fuel pump going bad?

Post by Hendog458 »

I've got an O-320 with what looks to be a standard aircraft style mechanical fuel pump. Lately I've been noticing if I run at higher rpms, like 2300+ RPM for a little while that the motor seems to start starving for fuel... motor starts stumbling and will shut off. But if I flip on the electric pump for a few seconds then everything goes back to running normally and the motor wont start stumbling unless i get back into higher RPMS again.

I don't think its a vacuum leak on the fuel lines, I checked all lines and fittings and they all seem fine.

The only thing I can think is the mechanical pump is going bad and cant feed enough fuel at higher RPMS? :dontknow:

Fuel flow is Tank > Racor fuel-water separator/filter > Electric fuel pump > Mechancical fuel pump > Carb

Anyone have any ideas on what could be causing this?

Thanks!

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Slidin Gator
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Re: Mechanical fuel pump going bad?

Post by Slidin Gator »

Have you replaced the Racor? Most electric pumps also have a screen on the suction side that should be checked/cleaned.

The mechanical has check valves that might be leaking due to corrosion or debris, the diaphragm is either good or bad, no real in between.
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

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Hendog458
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Re: Mechanical fuel pump going bad?

Post by Hendog458 »

The Racor filter is only a few months old. But I'll check that just in case it got gunked up.

I didn't think about the filter screen on the electric pump I'll check and see if that is causing the problem.

Thanks for the input

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Slidin Gator
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Re: Mechanical fuel pump going bad?

Post by Slidin Gator »

I forgot to mention, check the tank vent, them dirt dobbers can clog up a vent and burn up both the electric and mechanical in a 5 minute span. Ask me how I know...
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

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Hendog458
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Re: Mechanical fuel pump going bad?

Post by Hendog458 »

Thanks Slidin Gator. I went ahead and changed the racor filter, I don't think I had changed it as recently as I remembered. The carter inlet screen was pretty gunked up too. Hopefully that will do the trick.

I wont be able to check it out till i get on the water next weekend... I don't think my neighbors will appreciate full throttle pulls in the driveway. haha

Gary S
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Re: Mechanical fuel pump going bad?

Post by Gary S »

sounds like you need new neighbors. Hopefully inlet screen was problem. If not turn on electric when it starts to stumble.

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Re: Mechanical fuel pump going bad?

Post by Hendog458 »

Looks like the problem was either the inlet screen on the fuel
pump or the racor filter. Ran all night on Saturday and didn’t stumble once.

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Slidin Gator
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Re: Mechanical fuel pump going bad?

Post by Slidin Gator »

Hendog458 wrote:
Tue Aug 25, 2020 11:23 pm
Looks like the problem was either the inlet screen on the fuel
pump or the racor filter. Ran all night on Saturday and didn’t stumble once.
:thumbleft: :thumbleft: :thumbleft:
Most of the times when things don't seem right, I change the filter and all is good!

I run an electric with a check valve built in and then another check valve in a bypass line around the electric. They "T" back together on the engine side. With this setup the mechanical bypasses the electric when it is off. That keeps the filter screen on the electric clean so it is ready to go if I need it.
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.

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