Fuel Pump Pressure
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Tuned
Joined: Nov 2017
Posts: 303
Likes: 44
From: Cicero, IN
Fuel Pump Pressure
I have been having trouble with my flathead V8 F-100 project running exceptionally rich. I rebuilt the carb with .052 jets, checked the float level several times and a few other things. Today I tested my mechanical fuel pump and it was putting out 6 psi, well over the recommended 3.5 to 4.5 psi. So I think I found the problem.
The engine obviously has a repop mechanical fuel pump. Is there any way to reduce the pressure mine is putting out, like changing out the spring or a check valve or something? When buying a pump online (LMC etc.), do you have to specify the pressure you need? I see that they sell both single action and double actions pumps. Which is the OEM type pump? Is single action OK for a bone stock 239 Flathead?
The engine obviously has a repop mechanical fuel pump. Is there any way to reduce the pressure mine is putting out, like changing out the spring or a check valve or something? When buying a pump online (LMC etc.), do you have to specify the pressure you need? I see that they sell both single action and double actions pumps. Which is the OEM type pump? Is single action OK for a bone stock 239 Flathead?
Fleet Owner
Joined: Jul 2004
Posts: 27,303
Likes: 1,062
From: NM
This is a common problem with the repro pumps. The spring is the problem, as you say. Do you have an old pump you could swap springs with (assuming they are similar dimensions)? If not, it's an old trick to use a thicker gasket under the fuel pump stand to reduce pressure. You can't go crazy with that or the pushrod will pop out of the cup on the FP lever. The regular gaskets are quite thin, so making your own out of thicker gasket stock would be a good bet for as much pressure as you have to lose. As a last resort, I believe a couple of guys on the Ford Barn will service your pump to put it in spec (assuming a new Ford spring will fit it).
The dual action pumps are the ones that make vacuum as well as fuel pressure for running wipers on hills.
The dual action pumps are the ones that make vacuum as well as fuel pressure for running wipers on hills.
Thread Starter
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Tuned
Joined: Nov 2017
Posts: 303
Likes: 44
From: Cicero, IN
This is a common problem with the repro pumps. The spring is the problem, as you say. Do you have an old pump you could swap springs with (assuming they are similar dimensions)? If not, it's an old trick to use a thicker gasket under the fuel pump stand to reduce pressure. You can't go crazy with that or the pushrod will pop out of the cup on the FP lever. The regular gaskets are quite thin, so making your own out of thicker gasket stock would be a good bet for as much pressure as you have to lose. As a last resort, I believe a couple of guys on the Ford Barn will service your pump to put it in spec (assuming a new Ford spring will fit it).
The dual action pumps are the ones that make vacuum as well as fuel pressure for running wipers on hills.
The dual action pumps are the ones that make vacuum as well as fuel pressure for running wipers on hills.
Great advice! I will try the thicker gasket and see what I can do with the pressure. And the explanation of the dual action was new to me. Thanks.
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