Fuel pressure dropping while driving and under acceleration to zero at idle runs 4 lb electric Blue

flathead31coupe

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Am I seeing this photo correctly? You have the fuel lab regulator on top of a Holley regulator and the fuel lab one is feeding the Holley one?
Yes I opened the Holley fuel regulator all the way up and I am just using it as a t for the supply fuel line to both carburetors. The Holly regulator does no regulating. It is straight flow through used as a t only
 

flathead31coupe

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After rereading the plumbing planning notes, it said that you can plan the two side ports can be interchanged either outlet or inlet since this valve operates as a relief valve. Pressure is relieved from the regulator out to the rest of the fuel system by returning unused fuel back into the fuel tank
 

HSDemon

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Plug the return and see what happens. If it still does the same thing, then see if you can try another fuel pump. What fuel tank are you using?
 

flathead31coupe

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I guess so depending on how much gas I have in the tank I should be able to unhook the return line and just plug the bottom of the regulator and start it and see if it changes correct
 

Rat Bastid

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I guess so depending on how much gas I have in the tank I should be able to unhook the return line and just plug the bottom of the regulator and start it and see if it changes correct


Yes, but be damn careful and I’d probably have another set of eyes there to help. Blocking that return can and probably will cause a pressure spike which will blow fuel past the needle and seats.
 

HSDemon

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He said he had a Holley blue pump. Holley blue pumps are designed to run without return lines.
 

flathead31coupe

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I have a fuel lab regulator that is my main regulator. All I did with the Holly regulator is open it up all the way and use it as a t to supply fuel from fuel lab regulator to the carburetors
 

flathead31coupe

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What I was trying to explain in a earlier post I used an old highly regulator turn wide open as a t to supply both of my four-barrel carburetors. The fuel lab is designed for a return. I'm going to try to block the return line and run the supply line into a large container and see if I can get the 14 lb that the blue Holley fuel pump is capable of and see if it changes when I give it gas. I think that'll work as a test
 

Rat Bastid

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What I was trying to explain in a earlier post I used an old highly regulator turn wide open as a t to supply both of my four-barrel carburetors. The fuel lab is designed for a return. I'm going to try to block the return line and run the supply line into a large container and see if I can get the 14 lb that the blue Holley fuel pump is capable of and see if it changes when I give it gas. I think that'll work as a test

That will be a good test. I don’t think the Holley regulator is a problem since you are using it as a T.
 

TT5.9mag

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Did you gut all the parts out of the Holley regulator? Spring, check ball, and seat? If not it IS doing some regulating.

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flathead31coupe

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I also have another question. If I run a hose from the output of the regulator into a can and turn it on with it being wide open that will just be volume. It wouldn't have no pressure, correct?
 

TT5.9mag

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But just saying that the regulator is “all the way open” does not mean that it still does not create a restriction in the system. And if it creates a restriction you will see some pressure, depending on where you are measuring.
 

flathead31coupe

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I will check the regulator out this evening and see if I can do some tests to see if the pump is bad or not. I was just not sure about pressure versus flow
 

TT5.9mag

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When you do a pump output test, just test the pump by itself. With no restriction. That will give you a baseline when you test the rest of the system hooked up to the pump.
 

Rat Bastid

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So after rereading the posts that everyone replied to. What is the best way to test a fuel pump?


If you want to see how much pressure the pump puts out (who knows…maybe the relief valve in the pump is stuck open?) is to just use the Holley regulator and dead head the pump. Then measure the pressure in the line from the pump to the regulator. That’s a start.
 

TT5.9mag

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After you do the dead head test for pressure, do a timed flow test at zero pressure. Then you’ll know maximum pressure and maximum flow of your pump. Just run the output of the pump into a bucket for an amount of time. 30 seconds works. Then compare to holleys numbers. You may have to convert to whatever metrics they use to rate their pump.
 
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