[376Shovel]

When I shut my car off my fuel pressure gauge goes to zero with a Mallory 140 pump, Mallory non return regulator. Is this normal? With my old mechanical pump setups it always used to hang around 6 psi or so when I shut it off.

Also, my fuel pressure gauge bounces around like crazy and I can't get a proper reading. Right now it jumps between 6-8 psi. I tried a new gauge and same thing. Its not a liquid filled gauge and it sits right on my regulator.

 

[VinceS427bb]

that does not sound right, pressure should stay at pre-set regulator psi and then slowly bleed off. IIRC.
do you get the same results with the engine off and pump on?
your regulator may be defective or have derbis stuck in it...

 

[BB_Mike]

When I ran a comp 140 the psi would go to zero when the car was off. Every time I'd switch the car's ingition to give the motor 12 volts, I'd hear the pump do this "spooling" up sound as it built pressure. It did so quickly though. Kind of like a car's starter speeding up.

My pump pulled gas up out of the tank and was not gravity fed. Could be that I lost prime each time? I did not have a check valve in line.

My pressure regulator also jumped around, but that's just when the engine was running and shaking. With the car off, how much does the gauge bounce around?
What is the voltage at the pump with the engine not running and with the car running? Perhaps low voltage is causing slow pump speeds and those the surgeing at the regulator?

The COMP 140 is pretty easy take apart and check the magnets to make sure they aren't worn to the nubs. Making the pump suck fuel up and out puts more strain on it.

 

[onebad82z]

Holley black, blue and then Mallory 140 all have gone to zero as soon as I shut the car down.

But my fuel pressure has always been stable. Running an in car isolated Autometer pressure gauge.

 

[Slick71ss]

Mallory 140 into deadhead QuickFuel regulator with cheap Summit pressure gauge. Pressure drops to zero after shutdown. Gauge is steady while running. It might vibrate a little but no more than a 1/4 psi reading.

 

[nastynate]

Mallory 140 into Mallory return regulator with cheap pressure gauge. Pressure drops to zero after shutdown. Gauge is steady while running. It might vibrate a little but no more than a 1/4 psi reading.

Mallory 140 here also... X2

 

[376Shovel]

OK so the pressure drop thing doesn't seem to be an issue. That's good but now I have to check my regulator out for obstructions.

I also need to check the set screw on the pump itself to see what happens to the pressure if I tighten it or loosen it. I think it is an internal pressure bypass? Anyone know how that works?

 

[Jebchevelle]

The Mallory 140 has an internal bypass spring this is so it wont build too much pressure when used with a dead head regulator or non return style setup. I am not 100% positive but I believe that is why they bleed down when turned off. Every one I have used did the same thing. My BG 280 does this too and I was told that is the cause.
In the Mallory pump instructions there is a way to adjust the bypass if you want to put less strain on the pump. I have never tried it though.

 

[Camaro_fever68]

OK so the pressure drop thing doesn't seem to be an issue. That's good but now I have to check my regulator out for obstructions.

I also need to check the set screw on the pump itself to see what happens to the pressure if I tighten it or loosen it. I think it is an internal pressure bypass? Anyone know how that works?

It has an internal plunger with a spring that is set with a set screw. Factory pressure is 12-14 psi. If you turn the set screw in pressure increases, out decreases pressure.

If you were to go to a return regulator system, a plug should be used there.

 

[onebad82z]

The Mallory 140 has an internal bypass spring this is so it wont build too much pressure when used with a dead head regulator or non return style setup. I am not 100% positive but I believe that is why they bleed down when turned off. Every one I have used did the same thing. My BG 280 does this too and I was told that is the cause.
In the Mallory pump instructions there is a way to adjust the bypass if you want to put less strain on the pump. I have never tried it though.

It has an internal plunger with a spring that is set with a set screw. Factory pressure is 12-14 psi. If you turn the set screw in pressure increases, out decreases pressure.

If you were to go to a return regulator system, a plug should be used there.

Not to hijack or muddy the waters on the original intention but I want to ask.

Is there any reason not to adjust the setscrew to lower the pressure to say 8-10psi? I run 6 @ the carb inlet. Will lowering the output pressure take some load off the pump? Just a thought I had in reading these 2 replies...

 

[nastynate]

It has an internal plunger with a spring that is set with a set screw. Factory pressure is 12-14 psi. If you turn the set screw in pressure increases, out decreases pressure.

If you were to go to a return regulator system, a plug should be used there.

Do you mean plug the whole where the adjustment strew is?

 

[376Shovel]

It has an internal plunger with a spring that is set with a set screw. Factory pressure is 12-14 psi. If you turn the set screw in pressure increases, out decreases pressure.

If you were to go to a return regulator system, a plug should be used there.

This is great info and just what i needed.

Not to hijack or muddy the waters on the original intention but I want to ask.

Is there any reason not to adjust the setscrew to lower the pressure to say 8-10psi? I run 6 @ the carb inlet. Will lowering the output pressure take some load off the pump? Just a thought I had in reading these 2 replies...

I really want to know this too. this was actually my next question.

 

[nastynate]

Is there any reason not to adjust the setscrew to lower the pressure to say 8-10psi? I run 6 @ the carb inlet. Will lowering the output pressure take some load off the pump? Just a thought I had in reading these 2 replies...[/QUOTE] X2 Any answers or ideas from experience?

 

[dirtlips408]

Is this the Curley that used to have the 6.0 and ls3 heads? Ran 10's? If so man good to see ya back!

 

[dtrubey]

Is there any reason not to adjust the setscrew to lower the pressure to say 8-10psi? I run 6 @ the carb inlet. Will lowering the output pressure take some load off the pump? Just a thought I had in reading these 2 replies...X2 Any answers or ideas from experience?

Remember, you have to push the fuel to the front of the car against the launch.

 

[bracketchev1221]

Remember, you have to push the fuel to the front of the car against the launch.

And the racer with the answer!!! You use the high pressure to get the fuel up front under resistance that is trying to push it to the rear. It is best to have too much fuel and be able to recirc it or bypass it back to the tank than to run out.