High fuel pressure

[Cobraman]

I'm having some trouble getting fuel pressure down within reason my pump is rated at 240lph 45 to47 psi same as oem pump that is in the 97 Mustang Cobra. I also have a holley 12-188 pressure regulator that summit told me would work to get pressure down to the 4 to7psi range needed. So far that really hasn't worked out. I'm getting 12psi at the carburetor not running 9 with it running. The regulator is maxed just wondering how to get past the pressure issue. All my feed lines are an-6. My regulator is in the back right after fuel filter with a short 24" return line to tank I hope someone can point me in the right direction.
I really don't want to change fuel pump as I want to keep my options open for fuel injection later.

[gbranham]

Do you mean Holley 12-881? I don't see a Holley pressure regulator with p/n 12-188.

It claims to be good for 4.5-9PSI. When you say you have it maxed out, do you mean you have the pressure turned 'down' to the maximum, meaning the minimum? If you truly have it turned to the max pressure, that would explain why you're seeing 9PSI, since that's the max for this regulator. ;)

Greg

[Mike.Bray]

12-881 doesn't show a maximum inlet pressure so assume that's not it.

I do know Holley had a big recall on regulators so you might check into that and see if yours is on the list.

.

[cv2065]

Did you loosen the nut and turn it counter clockwise to drop the pressure or is it not responding to the set screw adjustment?

[Cobraman]

OK I my bad 12-881 I guess the fumes are getting to me. I called Holley and they said I have to much pump pressure for it to overcome. I called bull because there is nothing in the specs that say otherwise. They want me buy their $300 plus pump to make it work and replace mine. And yes I have turned the adjustment screw counter clockwise until it's ready to come out that got me from 20 plus # to 9# that's all she's got.
I guess my next step is to disassemble and check the inside sense they won't take it back now.

[rickshank]

It sounds like you're trying to use a regulator to take an EFI pump down to carb pressures?

[Papa]

I'm seeing a bunch of different external Holley carburetor fuel pumps for under $100, and in-tank pumps for $160 and up. I don't think you can typically use an EFI pump for a carb setup.

[Mike.Bray]

This one is designed to regulate down to low pressure for vintage carbs and you can change the spring when you upgrade to EFI:D Don't see why it wouldn't handle the inlet pressure.

https://www.summitracing.com/parts/hly-12-880

[Cobraman]

Thanks Mike I checked on the recall and I've had mine for sometime and it seems to be part of that recall so maybe I'll get something back. It just frustrates me that while I had them on the phone not one word was mentioned about recall.

Holley issued a recall in May 2025 for certain bypass fuel pressure regulators and kits manufactured between May 19, 2024, and February 18, 2025, due to a defect where a damaged diaphragm may cause a fuel leak, creating a fire hazard. The affected products can be identified by the date codes 140'24 through 049'25 stamped on the box. The recall covers specific part numbers, including 12-881, 12-886, and 12-887 and their corresponding kits. Holley is sending official notifications to consumers with instructions on how to identify affected products and receive a remedy.

[gbranham]

It sounds like you're trying to use a regulator to take an EFI pump down to carb pressures?

Yep. Pretty common, actually.

[gbranham]

I'm seeing a bunch of different external Holley carburetor fuel pumps for under $100, and in-tank pumps for $160 and up. I don't think you can typically use an EFI pump for a carb setup.

Its actually more common than you might think. It seems odd, but it works.

[Cobraman]

OK it was under a recall and summit was good enough to make good on it buy replacing it. They also talked me into upgrade to 12-841 much better regulator with my summit bucks I paid very little difference of about $60 win win :cool:.
Thanks Mike for the insight of the recall.

[Autonut]

It sounds like you're trying to use a regulator to take an EFI pump down to carb pressures?

Agree. Need to swap out the pump and use a non return pressure regulator for a carb set-up. IMO.

[cv2065]

Agree. Need to swap out the pump and use a non return pressure regulator for a carb set-up. IMO.

He shouldn’t need to swap out the pump. I used an Aeromotive A1000 regulator to take their 340 pump to 6psi and this build I’m using the Aeromotive X1 series to do the same. No issues and both have returns. As Greg said, it’s common practice.

[Jim Doak]

Cobraman,

FYI, I have a similar setup on my build; however, I'm using an Edelbrock fuel pressure regulator (174133). I've got a 255 lph in-tank pump with the pressure regulator located on the passenger side of the firewall. The supply line to and the return line from the regulator are AN-6. The regulator maintains a pretty steady pressure of 5.5-6.0 psi to my carb.

[Papa]

Its actually more common than you might think. It seems odd, but it works.

I learn something new every day on this forum.

[BUDFIVE]

Cobraman, since I just watched your first start video this may not matter anymore. Others on the forum may be interested too. Any of the 12-88x regulators with the 4.5-9psi range, including the 12-881, can be used with an in-tank EFI pump to regulate down to carb pressure values. The key is the return (bypass) line needs to be the same size as the feed lines. This is more important when regulating down from high pressure (EFI) values to carb values. There is a LOT of bypass flow. If the return line is too small, the pressure will build up on the return side and defeat the regulator. The flow WILL go somewhere and the regulator output pressure will rise. There’s a great video on this on ProM racings site.

I am using an in tank EFI pump, 12-887 regulator, 6AN feed, return and carb out lines. This is designed for an easy upgrade path to EFI if I want in the future-just swap to a footprint compatible 12-88x with the EFI values. Works great as I enjoy the first 250 miles on mine.

[MB750]

I did the EFI to Carb fuel pressure thing mainly because I wanted an in-tank pump. The fuel pumps I researched would consistently have lower pressure pumps mounting outside the tank in the lowest location possible. I didn't want that, they're too noisy, so I just bought an EFI style pickup with the 3/8" inlet and outlet and knocked the PSI down to 4.5 with an appropriate Holley regulator. I don't remember the specific one, but I can if it's needed.

I also ditched the crap FFR supplied fuel lines and converted to the flexible braided stuff.

[gbranham]

I learn something new every day on this forum.

You and me both, my friend. It's why I hang out here all the time. :)

[BUDFIVE]

For completeness, I’d like to point out the other major benefit of an in tank pump with a bypass regulator (as close to the carburetor as possible)—the fuel in the lines stays cool. Except at WOT, most of the fuel in the system bypasses and is recirculated through the tank. This is especially important after short stops which heat soak the fuel in the lines. Without a bypass system, heat soaked fuel must get pushed through the carb fuel bowls. In Texas, this prolongs a common “vapor lock” carburetor problem in summer time. I have been very pleased so far this summer with my system-no issues with heat soak starts despite high underhood temperatures-especially with the hood scoop not installed yet.

…..I wish I knew this in the 70’s…..

[Cobraman]

That was my next question I think I'm going to put it back under the hood thanks Budfive. I managed to get it started but still hav pressure issues waiting for replacement Regulator.

[sread]

As BUDFIVE mentioned above, if you are trying to regulate down to a minimal pressure, the return side flow is critical. It should flow at least as much as the pressure side.

[Ducky2009]

Just a thought. What size is your return line? To reduce that much pressure, seems that the return needs to be the same size as the supply. Too small of a line could restrict that much flow.