Fuel pressure regulators

[tdskip]

Hi guys.

The fuel pump on the Bugeye went and the replacement pump is putting out too much pressure.

Can I ask what is the collective wisdom on the right pressure regulator and where best to source it from?

Thanks!

 

[DrEntropy]

Holley. Summit racing. Don't be tempted to get one of the cheesy dial-style Tiawanese ones, they are poorly made and it's a crap-shoot to get one that works correctly. The ones I've dealt with which DO work need to be taped with aluminum duct tape to keep 'em from spontaneously "adjusting" themselves.

 

[tdskip]

Thanks for the fast response!

Most of the adjustable units listed at Summit have a floor PSI of 5 PSI+.

Don't I need closer to 3 PSI for the SU HS2?

 

[DrEntropy]

Hmmm. Best to stay lower than 5. If the needle and seat sets are of the "Viton" type you may get away with it. Is there a compelling reason you can't just get a lower pressure pump? What did you replace it (the original) with?

 

[Westfield_XI]

I am trying to answer the same question for my Westfield. It is hard to find a 3psi regulator that still provides enough flow at WOT. As I understand it, the regulators are adjustable restrictors: they all reduce flow as well as pressure. I am going to try with a low pressure high flow pump and regulate that. Carter makes a universal/marine rotary-type pump that supplies 5psi at high volume, I hope that lowering the pressure by only 2psi won't hurt the flow rate.
BTW I have been advised to have a driver visible fuel pressure gauge for the set-up. That way you can test drive it under real world conditions and see if it will hold it's setting too!! I think I will try to rig up something temporary with long fuel line rather than make a permanent installation.

 

[Morris]

You could pipe it like a EFI system. Make a return line and put the regulator after the carbs. For my EFI set up, I drilled a hole in my fill pipe, bent and stuck a long tube in there, and used GOOP to glue up the hole. It works perfect so far. To prevent building a lot of pressure and fumes in your tank, make sure your return tube goes to the bottom of the tank.

Really with this set up I don't think you would even need a pressure regulator.

 

[Sarastro]

Be careful not to make this too complicated. Yes, the regulator restricts the flow, but that's how it regulates the pressure--restricts it more when the flow demand is light, and restricts it less as more flow is needed. The result is a constant pressure at the outlet.

This also illustrates the problem with any type of pressure regulator--they often don't regulate well when the flow is zero. Specifically, imagine that the float valve shuts off, and the pressure rises. Then, the regulator's shutting off the supply won't reduce the pressure; you need some flow to bleed off the fuel between the regulator and float valve. Not usually a problem, but good to know.

Also, remember that you don't need a huge flow. For example, if your car gets 30 MPG and the flow is 10 gal/hour, this supports a speed up to 300 MPH! Now, obviously, the flow demand will be greater in hard acceleration, but even then a modest flow should still suffice.

Finally, you can get Holley regulators that work at low pressure: the 12-804 is spec'ed at 1-4 PSI. That should be fine for a Sprite. I don't have any specs on flow limits, but the fact that it is not specified probably indicates that it's not an issue. They're used on cars with much greater flow requirements than Sprites, for sure.

My solution was to use a pump whose backoff pressure was almost exactly the same as that of my mechanical pump, about 3 psi. A simple solution to the whole problem.

 

[DrEntropy]

Thank you, Steve for the Holley part number.

And for:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] My solution was to use a pump whose backoff pressure was almost exactly the same as that of my mechanical pump, about 3 psi. A simple solution to the whole problem. [/QUOTE]

 

[regularman]

I bought one of these to try and solve a problem with a pinto engine that I had. I found it to be a waste of money and did nothing to solve my problem. I agree with the return line solution to fix the problem. This also solves a problem with fuel expanding when the engine is shut off hot and building pressure and forcing fuel past the needle and flooding the engine up restart.

 

[Westfield_XI]

Also, remember that you don't need a huge flow. For example, if your car gets 30 MPG and the flow is 10 gal/hour, this supports a speed up to 300 MPH! Now, obviously, the flow demand will be greater in hard acceleration, but even then a modest flow should still suffice.

Speaking to Spridget racers with similar engines to mine it seems that there can be a problem with float bowls running dry on long straights when using the facet pump with a regulator. I am running a 1380 with 2 modified SU's.


My solution was to use a pump whose backoff pressure was almost exactly the same as that of my mechanical pump, about 3 psi. A simple solution to the whole problem.

Which pump are you using?

 

[regularman]

I think you will find that the old SU fuel pumps worked differently than newer electric pumps. The midget is the first car I ever had with an elecric fuel pump(besides EFI) that did not have a problem with overpressure and forcing past the needle at times. I always had a switch to cut it off for a bit if that happened.

 

[Sarastro]

To answer the question, I'm using a Facet pump, model 40105. It's rated 3.0-4.5 PSI at backoff, so maybe I just got lucky with the pressure. If you don't want to risk getting something with 4.5 PSI, there are others rated at lower pressure. I found the flow vs. pressure curves on their website. Even the very low-pressure pumps with ~2 PSI backoff have good flow at ~1 PSI back pressure, which is probably about as high as it gets on a Sprite.

 

[Hap Waldrop]

Ditto on the Holley regulator, that's all I use on the race cars, you will need to plumb in a guage though to see what the pressure is. If you don't want to put a guage in the dash you can do a couple of things, put one under the hood permantly or just hook it to the regulator when adjusting, then un hook and plug the the hole with a NPT cap plug, all the threads going into the Holley regulator are NPT.

 

[ChrisS]

I was using the Holley 12-804 2 port regulator and had problems going from wide open throttle to idle and hot idle in general. I changed it out with another 12-804 and had similar problems even with a different pump. Then I changed to a Mallory 4309 3 port and have had no problems with it. The 12-804 was in use for years so I don't know what changed but I was setting the pressure at 2 psi at the carbs at fast idle and it would drift to 7 psi at idle and with the engine off. At this point fuel was being pushed out of the carbs.

 

[tdskip]

OK - so now I'm confused again (typical) about the best course of action. <grin>

Since the replacement aftermarket pump isn't correct for the car (not my doing) I am wondering if simply installing the 12-804 pressure regulator is going to fix this.

Do you think I should I try a lower pressure pump or the Holley 12-804 regulator?

Is there a Moss (or other vendor) fuel pump that people have had a good experience with?

Thanks!

 

[Billm]

Use the Faucet low pressure pump! Forget the regulator.
Bill

 

[jlaird]

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[tdskip]

This one?

https://www.aircraftspruce.com/catalog/eppages/facetpumps.php

 

[DrEntropy]

The very one.

 

[Sarastro]

My suggestion is that the Holley regulator is only about $25, so it's worth a try. It will probably work fine for your purposes. A second, equally reasonable possibility is simply to replace the existing pump with one of the lower-pressure Facet pumps. They seem to have a good reputation; the only complaint is that they can be noisy--but mine isn't, and I suspect that if you install them precisely as instructed, they won't be. You can get a Facet pump for about $30, if I remember correctly.