TheSamba.com :: View topic - Holly 12-804 fuel pressure regulator won't go below 3

Fri Feb 11, 2022 7:34 pm

I installed a Holly fuel pressure regulator on my 1970 ghia following the Heidi and Franny Youtube video on the topic. Before the install, my pressure was consistently at 5. in the video, the lady talks about adjusting it to 2.5 for the best results. No matter what I do, I can't get it below 3.0. You're supposed to be able to turn the screw on the top to get it to move and I can but it won't go below that.

Any ideas on what the issue might be? (please don't tell me to remove the regulator and change the pressure by shaving the rods or raising the pump...I already opted for the regulator router :) )

Fri Feb 11, 2022 8:43 pm

Is this a new, or used regulator? I’ve seen the diaphragms get stiff, and cause strange things to happen pressure wise on used regulators. The low/high pressure regulators are the same with the acception of the pressure spring. Maybe the incorrect spring was installed.

Fri Feb 11, 2022 10:47 pm

I've never seen a fuel pressure regulator that small and cheap that works good.

That's not the information you are looking for, I'm sorry. BUT, do you know?

If you are new to the game then it might impact how much time you decide to spend messing with that thing if you knew that... the majority of mechaincs who have been in the game a long time expect that cheap little regulator to be garbage. Or you might want to prove them wrong. maybe they are wrong.
Either way good luck.

https://vwparts.aircooled.net/Fuel-Pressure-Regula...ulator.htm

Sat Feb 12, 2022 12:59 am

Change the pump.. or change the damaged regulator. The harder you tighten the screw the more damage you do to the needle seat..
That diaphragm/ demand valve design of regulator combines too much pressure at zero flow if old and damaged AND fuel starvation at high flow if the pump pressure is too low..

Buy a Carter pump and trash the regulator..

On my T1 engine I have a brand new SSP E10 compatible stock style mechanical pump. Twice the price of the generic new pumps but it does deliver 3.5 psi without messing with shims.

Sat Feb 12, 2022 7:15 am

Most 0 to 15psi gauges I have used arent very accurate below 5psi.
Generally gauges are close to accurate thru the middle of the gauge range but way off at the lower end of the range.
I now have a 'Winters PLP series, 0 to 5psi gauge. I use this to set Holley Red FPR's.

Sat Feb 12, 2022 11:45 am

dungeoncrawl wrote: I installed a Holly fuel pressure regulator on my 1970 ghia following the Heidi and Franny Youtube video on the topic. Before the install, my pressure was consistently at 5. in the video, the lady talks about adjusting it to 2.5 for the best results. No matter what I do, I can't get it below 3.0. You're supposed to be able to turn the screw on the top to get it to move and I can but it won't go below that.

Any ideas on what the issue might be? (please don't tell me to remove the regulator and change the pressure by shaving the rods or raising the pump...I already opted for the regulator router :) )
Read this info.
https://www.thesamba.com/vw/forum/search.php?searc..._chars=200

Sat Feb 12, 2022 6:12 pm

[email protected] wrote: Is this a new, or used regulator? I’ve seen the diaphragms get stiff, and cause strange things to happen pressure wise on used regulators. The low/high pressure regulators are the same with the acception of the pressure spring. Maybe the incorrect spring was installed.

It's brand new. Ya know, today I got out there and I was running it for the first time in several weeks and the pressure was at 1.5. So I started turn the screw on the regulator and it started creeping up to 2, then 2.5. So I left it there and drove it around town. It was still at 2.5 when I parked it so 'maybe' I'm okay.

Sat Feb 12, 2022 6:13 pm

Dougy Dee wrote: Most 0 to 15psi gauges I have used arent very accurate below 5psi.
Generally gauges are close to accurate thru the middle of the gauge range but way off at the lower end of the range.
I now have a 'Winters PLP series, 0 to 5psi gauge. I use this to set Holley Red FPR's.

This one is a 0-5. Working better today though. As I stated in response to another post today, it's acting totally different today then it did a couple of weeks ago for some reason.

Sat Feb 12, 2022 6:17 pm

modok wrote: I've never seen a fuel pressure regulator that small and cheap that works good.

That's not the information you are looking for, I'm sorry. BUT, do you know?

If you are new to the game then it might impact how much time you decide to spend messing with that thing if you knew that... the majority of mechaincs who have been in the game a long time expect that cheap little regulator to be garbage. Or you might want to prove them wrong. maybe they are wrong.
Either way good luck.

https://vwparts.aircooled.net/Fuel-Pressure-Regula...ulator.htm

I'm definitely new to the "playing mechanic" game. I installed it based on the recommendation from the Heidi and Franny Youtube channel. I definitely had a gas smell in my garage and the car was super hard to start. When I threw the fuel pressure gauge on there and it was at 5, it seemed to validate what they were saying (high pressure shooting fuel into your carb making your garage smell and car harder to start next time". Since I added the regulator, the fuel smell is gone and the car does start a little easier. Today, after trying things a couple of weeks ago, things def worked better and I was able to get it from 1.5 psi to 2.5 by turning that screw unlike last time. I'm going to keep my eye on it.

Tue Feb 15, 2022 9:38 pm

12-804 regulators are factory set to 2.8 psi.

A couple of things people do not seem to understand about these 1-4 psi regulators.

First the maximum pressure you can put into the regulator is 7 psi.
The minimum pressure you can put in and have the spring and diaphragm work correctly is 5 psi.

You CANNOT put 4 psi into the regulator and adjust it down to 2.5 accurately,4 psi input is too low for the regulator to react correctly. . But you CAN put 5 psi in an adjust it down to 2, 2.5 or 3 or whatever you want.

So in essence the 12-804 regulator is only good for adjusting down 5-7 psi of pressure.

If you have an old 12-804 that starts acting up the diaphragm has probably gone to stiff from the new Gas with ethanol additive.

Quick Fuel makes an E85 tolerant diaphragm that fits the Holley. This solves the problem.