Street Rat

My latest problem concerns fuel pressure. I have a Holley bypass regulator which uses a return line to the tank. I recently installed an Autometer fuel pressure gauge. I was shocked to see that I have a fuel pressure drop to zero on hard acceleration.

I purchased a new electric fuel pump and regulator thinking that either of these would fix my issue. They did not. I have no restriction in my 3/8" fuel line at the present time.

I have read here that some of you use restrictions in the return line to up the pressure to the carburetor. I have seen numbers from .020 to .060 size restrictions used.

I have been experimenting with different size restrictions in the return line. I have yet to find the right combination to get this problem solved.

My question is what size restriction are you using in your return line? What worked for you?

jnb5101

I installed a brass T fitting in the supply line. Then soldered a copper plug in the offset line and drilled a 050 hole in it, and fed that to the original return line. Never had a problem, although I never tested the pressure with a gauge.
Someone smarter than me removed the bore plug at the front of his Qjet fuel inlet, and threaded a fitting into the bore and used that for a return line. A very elegant solution.

mikem350

Any restriction should help...maybe post a diagram of your fuel lines and describe pump manufacturer, fuel filter, and engine HP, etc.

Street Rat

I'm getting a drawing together now.

97C5

Shouldn't need any type of restriction to boost pressure. That is the job of the pump and regulator.

What pump and regulator? Where are you picking up the fuel pressure? Mechanical or pressure sensor?

Street Rat

The pump is an Electric Holley 12-150 rated 140 gph @ 7 psi
The regulator is a Holley 12-841 with a return port

I'm getting my pressure readings at the inlet line at the carburetor with an Autometer gauge with pressure sensor. I have a liquid filled gauge at the regulator also. I sent my gauge in and Autometer said it was ok. They sent it back with a new sensor. So I think those can be ruled out.

97C5

Looks like good parts...

For the dumb questions...

You're running lines as follows:

Fuel Pump Out -> Regulator In
Regulator Out -> Carburetor
Regulator Ret -> Tank


Have you tried moving the autometer sensor to the regulator to see how it responds under load?

Do you have full voltage and good ground at fuel pump?

Jamess411

I have never heard or seen that type of problem…if anything usually it is too much pressure not lack there of. Something else has to be going on…maybe your pickup in the tank is losing prime under acceleration? or the pickup collapses when the pump needs to draw more fuel under high use? Most carbs only need about 3.5 PSI of pressure and your engine possibly could only use up to 14 gallons in an hour if you got 5 mpg at 70 mph. That is 10 percent of its capacity to pump @7psi. Or like 97C5 stated a routing problem with lines.

ykf7b0

Do you have aluminum fuel lines that you routed yourself?

427Hotrod

The regulator should be controlling whatever is bypassed. If the regulator isn't sending it out, the size of return doesn't matter. Sounds like either the regulator isn't working right or the pump can't handle the flow and keep up. Have you tested pump flow? If pump is capable of 7PSI...what do you have it set at?

In tank filter OK? Would be best to have the in tank filter gone and use a large screen type one if you want to that can catch debris (100 micron). I don't use anything in front of my pumps....I just pay attention to what goes in the tank.

I assume pump is set up at rear of car as a "pusher" right off the tank? Those pumps don't "pull" very well.

Is tank vented well? Through the cap or external?

Does regulator have a vacuum port?

JIM

Street Rat

97C5

schematically, that looks good. The #6 line from reg to carb... are you able to route that (or put another in place) to a portable gas can to check flow?

Street Rat

They are great questions.

Interesting thought about moving the sensor.

I'm assuming I have full voltage. I need to check that for sure.

No doubt about the ground. It's good.

Street Rat

No mine are braided hose using AN fittings.

Street Rat

I'll check the voltage at the pump, do a free flow test, and move the sensor to the regulator if I can. That should be a good start to find something.

Thanks for the ideas.

Street Rat

Haven't tested the flow yet.
In tank filter gone.
Pump is in front of tank.
Tank vented through cap although I haven't checked it with the cap off.
Regulator does not have a vacuum port?

Jamess411

I might have the solution for you. After doing some internet research I found a few guys that had a similar problem. Remove the line from the tank side of the pump and look in there….they said it comes with a filter/screen installed from the factory. Since you already have a filter on the inlet side between the tank and the pump you do not need it.

Street Rat

The original filter screen has been removed. That line is now used as a return to the tank. I have used two #8 fuel bungs on the bottom of the tank to gravity feed the pump.

flyeri

See this post:

https://www.corvetteforum.com/forums...d-by-lars.html

You will need a non-return style regulator.

Street Rat

I'm beginning to sense that the regulator is simply not receiving a good fuel supply through the 40 micron filter OR the pump is simply not being supplied enough fuel to up the pressure.

A flow test through the 40 micron filter will confirm this. If it flows well then I'll free flow the #6 line off of the regulator.

Thanks for the suggestions and threads so far.