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Marine Power 5.7 carbureted engine flooding intermittently

Billnet

New member
Have a fuel delivery problem that is driving me crazy. I have a marine power 5.7 gas carbureted engine. I recently had an issue where my Holley 4150 was getting flooded out by too much fuel coming from the carter 7 psi electric fuel pump after coming off plane. Filled the fuel bowls until over flow. I figured it was a broken float or needle valve issue so I took the Holley apart for a rebuild and found lots of corrosion so I decided to get a new carb. QFT M-650. When I installed the new carb I also put in a fuel pressure gauge between fuel pump and inlet to the carb. Installed all and ran great. Pressure gauge ran 6.5 psi. All good for about 3 hours of running on plane and back to idle several times.

Then later in the day I noticed the pressure went down to 4 psi from the 6.5 psi. Fuel level in the bowls did not change much from being in the center of the sight windows and boat still ran ok. I was thinking bad anti siphon valve of clogged filter and would check that out back home. But then after running on plane for about 5 miles I came back to idle the boat started to stall bad and noticed the fuel pressure reading 12 psi and not a steady ready. Very erratic movement of the needle in the gauge. float chambers were full of gas, so full that gas was coming out of the j tubes. Same exact problem as I had with the previous carb installed.

What the heck can make a fuel pump rated for 7 psi max run to 12 psi and flood out my carb?

I have all new 3/8" fuel lines and all hoses are tight.
New 10 micron fuel filter/water seperator
brand new carburetor
 
I'd suspect there's crud in your tank that may have a part in this....have you checked to see if there is any contamination in the tank? what does the inside of the pump look like? Crud can make the check valves operate erratically....

12 psi of fuel pressure is a bit high for most float & inlet valve combinations so the overflow out of the j-tubes is consistent with the pressure reading. If the pump is causing this, a new carb wont correct that problem...
 
I'd suspect there's crud in your tank that may have a part in this....have you checked to see if there is any contamination in the tank? what does the inside of the pump look like? Crud can make the check valves operate erratically....

12 psi of fuel pressure is a bit high for most float & inlet valve combinations so the overflow out of the j-tubes is consistent with the pressure reading. If the pump is causing this, a new carb wont correct that problem...

Thanks for the reply.

The little screen inside the intake to the fuel pump is clear. I just replaced the 10 micron fuel/water separator filter that's connected right from the fuel tank. The only thing I have not checked yet is the tank pickup and anti siphon valve but my thought was that would cause a lower fuel pressure as opposed to high pressure. The gas in the fuel/water separator is clean and had no water.

Yes I agree the issue is not in my carb. Just could not understand why the pump was putting out higher pressure than rated for. Pump cost 140 bucks so I was trying to eliminate all other possibilities.
 
If you had corrosion in the fuel system, it hints at water being present....when the boat is out on the water, whatever is in the tank usually gets mixed up....checking the antisyphon valve would be prudent....making sure there isn't anything but fuel in the tank would be prudent as well...

a regulator can mitigate the pressure peaks but I'd be inclined to figure out what isn't correct in the baseline setup.....
 
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