View Full Version : Mechanical Fuel Pump Problem....maybe. Convert to Electronic Fuel Pump

12-17-2009, 11:58 AM
I've been chasing a huge problem for a couple months now. I will post more details once I've solved the problem, to hopefully benefit someone else down the road. In the mean time, I need some help/input.

Has anyone ever seen a Mechanical Fuel Pump fail, and as a result it pushes too much pressure. I have a Carter Mechanical Fuel Pump that is rated for the Holley 4160 Carb I have and should be delivering 6-8 psi. I haven't put a pressure gage on it yet, because I'm still tracking one down, but I suspect that is the cause of my problem.

My problem is that my BRAND NEW Holley Carb is flooding out the engine. Fuel blows right past the needle valve and keeps flowing into the intake even after you let go of the key. I've checked the needle valve, the seat, the float....all work fine and seal. The fuel is clean, and there is no water in it. All fuel lines are brand new. I know the Carb works because it has been bench tested on another engine. So, for whatever reason, my setup is causing it too flood.

My intuition tells me that if a Fuel Pump fails, it will fail by loosing pressure, not increasing pressure. But I think there is a pressure regulator built into the Pump that may have failed. Obviously I've got a pressure test that I need to perform, but again, in the mean time, can anyone share with me an experience about a mechanical fuel pump pushing too much pressure???

One more thing, has anyone converted from a Mechanical Fuel Pump to and Electrical Fuel Pump. I'm considering the Holley Blue Electrical Marine Pump.


12-17-2009, 12:26 PM
I had a similar problem. One of the flat plugs on top of the fuel bowls was loose. This allowed the needle assembly to continue fuel flow after the float topped out.

12-17-2009, 01:21 PM
The fuel pressure is controlled by a spring pushing against a diaphragm inside the fuel pump housing. If the pump is the correct one for your application, I can not imagine how it could produce too much pressure. The likely culprits in your situation are high float level, leaking needle valve, sinking or binding float or debris in the fuel (causing the needle valve to not seat properly).

12-17-2009, 06:05 PM
"One of the flat plugs on top of the fuel bowls was loose"
tph - maybe our carbs are slightly different, because mine does not look exactly like the one in your pick, and i don't have any flat plugs on top of my fuel bowl. not hat I know of anyways. The only adjusting I can do is internally. So I have to remove the primary bowl to adjust the float/needle.

T-Rager - I got the carb from skidim, and they've bench tested it for me. said it runs like a top. I sent it to them to test, after I was having problems with it. They said it was clean as a whistle on the inside. They didn't do a thing to it. Just took it out of the box (from me) slapped it on their test engine, and it fired right up. So, I know I've got a brand new carb that works. That being said, I'm hear what you're saying 100%. I can't imagine the pump not working correctly. I bought it from skidim as well, just 2 years ago, and I know it's the right size pump. And my boat was running until 2 months ago. So yes, it's hard for me to imagine how a failing pump can push more pressure than before it failed, but if that's not what is happening, then I don't know *** is going on!

As a side note: I talked to a good friend of mine who builds muscle cars. TONS of experience for 20 years working with holley carbs, ford 351s, etc, etc. He thinks its the fuel pump. He can't explain why, but he thinks it's the fuel pump none the less.

I'd love to know if anyone else has any insight. I really appreciate you guys already chiming in.

12-17-2009, 10:34 PM
I would really focus on the fuel pressure test. Sounds like the carb has been "tested". I just went in circles over an engine repair and probably measured the fuel pressure 10 times, just to keep eliminating it as potential problem.

12-18-2009, 10:37 PM
You should answer your question by connecting up a gauge and checking the pressure that the fuel pump is putting out......take away all the guessing.

A low cost gauge/tester will run you less than $20 and will come in handy for checking engine vacuum as well. Some parts stores may even loan you one.

02-03-2010, 02:25 PM
Hi everyone. Just wanted to post an update. I found a pressure gauge and the pump was pushing out 7.7 psi, which is dead on. So my fuel pump was not the issue. After months of troubleshooting, a new carb, all new electronic ignition components, plugs, wires, coil, etc, etc.....it all came down to one simple $20 part: the ignition switch was bad. It was a 3 position switch. The off position worked, the start position worked, but the on/run position was dead. So the engine would turn over and act like it wanted to crank, but as soon as I let go of the key (return to the on position) the engine would die. This little dead switch was giving me all sorts of erroneous symptoms. Well, I replaced the switch and with all the other new parts, I've got a boat that's running better than it has in years! I definitely spent more money troubleshooting than I might have if I had discovered the bad switch early on, but the end result is awesome. So, to everyone out there, don't overlook the little stuff! I finally realized the switch was bad when I noticed the gauges on the dash weren't jumping on when I flipped the key to the ON position. Anyhow, hope this helps someone out there.

02-03-2010, 04:45 PM
So all the extra fuel you were seeing was the result of your bad ign switch turning off the spark as soon as you let go of the key. Every time you cranked her up you continued to build up more and more raw fuel.

All makes perfect sense now, huh?