Hot Rod Forum : Hotrodders Bulletin Board

Hot Rod Forum : Hotrodders Bulletin Board (
-   Hotrodding Basics (
-   -   Holley billet fuel pressure regulator issue. (

eric32 05-10-2019 08:16 PM

Holley billet fuel pressure regulator issue.
Hello guys I am starting another post and I am having some weird issues and tried to research things and I can't come up with anything. I just hooked up a carter mechanical fuel pump in replace of my electric in line fuel pump.

I have a holley 12-841 billet fuel pressure regulator that has a bypass line and adjust from 4.5 to 9 psi. I finally had everything plumped up today and gave it a start and the fuel pressure was at only 3 psi and my gauge is on my fuel rail at my carb and not on the regulator which has a gauge port for one. I tried adjusting it to give me about 5 psi and no matter how much I adjusted it the thing would not go over 3 psi and if I tried to lower it then it would go down to almost zero but I left it up as high as 3 psi.

When I squeeze my input hose coming from my fuel pump into the regulator it will make it bump up just a hair if that means anything. I even tried to squeeze my return line off just to see if it would change anything and nothing it still stays steady at 3 psi. I took it out for a drive and it seemed to not be starving for fuel and even on the highway at cruising speeds and giving it some gas it does not seem to run out or anything.

With my previous electric fuel pump even with the return line it started up at 6 psi then would drop way down when it got hot then it would just go to zeo and my lines are routed away from any heat source and I think my electric pump maybe was just going junk.

My mechanical pump is a carter series m4685 and says it puts out 7psi according to summit and I ran the same pump on my last build with no regulator and my pressure gauge would fluctuate betweent 4 to 7 psi as the pump would work. Could there possible be a difference in the reading of the psi from the regulator port vs the port on my carburetor fuel rail? 3 psi is pretty low and I know my engine would not last long if I really got on it for a long enough distance. I have already thrown a lot of money at this thing and now this mystery. Anyone hear of this before. All lines are nice and routed good and no restrictions.

BogiesAnnex1 05-10-2019 10:52 PM

Sounds like this pump only gets to 3 psi

If you're not using a bypassing regulator you old electric pump probably overheated then pressures go down.

For a carburetor of factory TBI, I like to run either a high capacity in tank low pressure (15-20 psi) TBI pump or a pair of standard Low Pressure TBI pumps in parallel with a bypassing regulator back to the tank. This insures plenty of cool fuel with a steady pressure at the carb regardless of engine consumption.


TommyK 05-11-2019 06:25 AM

Holley says that regulator is to be used with electric fuel pumps only.

eric32 05-11-2019 07:48 AM

Forget my last post I erased my statement but I don't understand why just because a regulator has a built in return line that it can't be used for a mechanical fuel pump application. I am going to bypass the regulator and hook my pump straight up to my carb and see how much the pressure changes or if at all. If it does not then I guess I will have yet again get another pump with more pressure. I guess I might need start saving again and get the fuel regulator with no return in it and then buy a fuel pump with a return line. This stuff is a headache and all because that piece of crap holley pump that I had for a year and it just must of been a dud as it would keep loosing pressure even after I installed the return line and everything else and the pump was running cool. I don't know what happened with it as as its being gravity fed by the tank and sat below it.

O well the art of fixing things and throwing out money. I will fix this the right way however much its going to cost me in the long run but it will be a while gotta get some more cash rolling in. I guess I will leave it as is for now since I did drive it and had no issues I just need to not be getting on it that's all. Thanks Tommyk for pointing that out I did not see that part but it still does not make sense to me though.

chasracer 05-11-2019 12:36 PM

Let's not forget that 90+% of this is made off-shore now. WE are Quality Control now, not the manufacturers so it could be just a bad pump. I would pull it and send it back for a replacement.

ericnova72 05-11-2019 02:36 PM

Holley may print that but it is mechanical nonsense....there is nothing special or different about any fuel pressure regulator that makes them "electric fuel pump only" or " do not use with mechanical pumps"....that's just hogwash.

Think about how a regulator doesn't care if it is fed pressure from a electric rotary pump, , electric plunger pump, mechanical plunger pump, or a fuel tank mounted 25" above the car using gravity feed to provide the pressure.

Gauge location doesn't matter either, a gauge located anywhere on the output side, be it in the regulator, in the line with an adapter 1/2 way to the carb, or right at the carb inlet is going to all read the same pressure.

The ideal mounting point for a return regulator is after the carb....line goes from pump to carb feed line or log, from back end of feed line or log to regulator, and then to return line.
This way, if the carb needs ever drop the pump puts out, nothing is sent down the return, return is only active when there is pressure above the set regulation point, thus meaning extra fuel is present so the return opens and sends the excess out the return port.
First link is a little oversimplified at the carb inlet not showing the feed lines or log...but the second link shows exactly how it should be.,2,6

eric32 05-11-2019 06:23 PM

Thanks for the links. I will try a different pump first before I do anything else. Please forgive me as I am knew for installing a return line and my first time doing my fuel line system like this. In the past all I have done is put on a fuel pump and was done and needed no regulator or return line but with the different fuels being what they are nowadays a return line system can only help.

Now since most mechanical pumps don't have a return line port on them if I were to swap out regulators somewhere down the road and I got a non return regulator and my mechanical fuel pump has no return line feature and I want to keep my current fuel rail on my holley what parts would I need to make this happen that would not cost an arm and a leg and not being exotic parts?

Forgive me if I sound dumb but I have not overly researched stuff on fuel line system hookups and stuff and my truck is not being raced at the track or anything else as over the years even just a stock pump has served me well just fine for what I do as I just cruise.If I just buy a mechanical fuel pump that puts out more pressure then I don't see any reason why my current setup would not work but like I said I am new to this part. Thanks everyone so far for your help.

alwill923 05-12-2019 01:15 PM

Is the gauge any good? Take the regulator out of the system and run the line directly to the carb. Put the pressure gauge in the line. This will tell you exactly what pressure the pump is putting out.

eric32 05-13-2019 09:16 AM

The gauge should be good as before I even had the regulator hooked up when I first fired up my truck it would read 6 psi from my previous electric pump and I do have it on my list to unhook my pump from the regulator and straight up to my carb to see if it is only putting out 3 psi. If that is the case then the pump is gonna have to be replaced even though its brand new but the crap you buy nowadyays I have read many positive reviews on the carter mechanical fuel pumps on summit but a few negatives here and there where people were getting pumps putting out over 10 psi at times and they were never meant to put out that much.

The quality control nowadays is like a dinosaur and that being extinct. I got another pump on the way and if that fails then I will buy a high pressure pump that requires a regulator and see how that goes but I am doing on thing at a time. I also fount out the other day I have something going on somewhere else that is causing me problems something ignition related and I checked my timing and its coming out ok but something is going on.

My MSD box might be going bad after only 5 years of use. You drive at lower speeds and it wants to sputter faintly and then once you get up to higher rpm cruising speeds its runs fine and i know its not my carb as i just rebuilt and put that thing together a few months ago and even did a few adjustments on it to see and no difference on that part. So I have a check list of things that I have to now try to sort out and find my culprit.

I got me a new Petronix HP box to replace my MSD as I have read many people having problems with the quality of there boxes after a short time going bad and stuff. I am putting new plug wires and everything else on it as a precaution since i had a pare on hand. That is why years back I started to buy some extra parts to keep on hand such as ignition stuff and carb stuff and other things so like when this stuff happens I already have it bought and just pick it off the shelf.

It seems nothing can last nowadays anymore.

36 sedan 05-13-2019 03:12 PM

JMHO, 3lbs free flow may be correct for a pump that puts out 10lb static pressure. And, 3lbs free flow (constant at the carb) may not be a problem for a carburetor as long as the flow rate keeps up with demand (pump can maintain 3lbs or close to it at sustained WOT). Carburetors depend more on flow (volume) than pressure.

Your sputtering at low speeds could be carburetor related, as in the idle restrictor too lean or gummed up, which will effect the transition circuit and cause sputter. Try cleaning the idle fuel and air passages. Also take a look at your plugs to see what the idle/transition mixture looks like it may need to be adjusted.

MSD or any type of multi spark ignition requires REALLY GOOD POWER and GROUND connections, these should be sourced directly from the battery. Many failures can be attributed to incorrect wiring practices. Further complications with multi spark ignitions can be caused by incorrect spark plug wires (too low of impedance) and believe it or not the cylinder heads not grounding well, a separate ground wire to each head is preferred with multi spark. And always disconnect the MSD's power, ground and tach wires when welding on the car.

"It seems nothing can last nowadays anymore." We are starting to sound like our fathers, lol!

55 Tony 05-13-2019 03:37 PM

Carter's psi ratings
You have it all wrong. I went through this with Summit and then called Carter. If it says "Maximum Pressure (psi): 7 psi" That is all it means, maximum. Doesn't mean anything for minimum. If you dig deeper and find it to says 3 to 7 psi and it's puts out 3 max, they say it is within spec! Just like it says, 3 to 7. It's at the low end but it's in there. I returned my first electric fuel pump from them and got another with a higher "range". BTW, I returned mine for a full refund and didn't pay shipping. Where they ask why it is being returned I put "The ad is misleading" and added the pump pressure story.

36 sedan 05-13-2019 05:38 PM


Originally Posted by 55 Tony (Post 4672221)
You have it all wrong.

Ahhhh, what part do I have wrong???

55 Tony 05-13-2019 07:41 PM


Originally Posted by 36 sedan (Post 4672233)
Ahhhh, what part do I have wrong???

I don't know if I was addressing you, but if you read what I wrote about how Carter rates their pumps, you may catch my drift. OK, for example, I bought an electric pump from Carter that was rated for (I'm guessing a little) from 3 psi to 7 psi. The thing wouldn't go over 3 psi. Even dead headed into a gauge, still 3 psi. Carter says that is correct and within the "3 psi to 7 psi" they rate it at. If the pressure was only 2.5 psi, then it would be defective. At 3 psi MAX, it is within its specified range.

So the bottom line is that if buying a fuel pump from Carter, if you want 6.5 psi, you better make sure that the pump is rated for 6.5 psi to ? 12 psi?. The low number could very well be the highest it ever goes! And they call that good.

55 Tony 05-13-2019 07:53 PM

Let me add that if the Carter pump says max 9 psi, all that means is it should never go over 9 psi. It in no way means that with no fuel flow it will reach 9 psi. You would need to know the low psi specs from them to find out the lowest it might put out.

36 sedan 05-13-2019 08:38 PM

What I was trying to say is, carburetors do not need 9psi, they will operate perfectly at 3lbs as long as the pump can supply the fuel volume needed (needs to be more than what's burned at WOT). Low pressure is not detrimental to a carburetor (IMHO anything above 5lbs is asking for trouble anyway). And keep in mind, with a mechanical pump volume will usually increase with rpm, as will static pressure (dead headed). While 3lbs at idle (600-800rpm) may seem low, it could well have 5lbs or more at 1500-2000rpm.

As long as the pump can keep ahead of the fuel demand (amount of fuel burned at WOT) and not reach pressures detrimental to the carb all will be good. However, starving the carb at WOT (lower flow rate than motor uses at WOT) is very detrimental to the motor.


All times are GMT -6. The time now is 12:30 PM.

Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.