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fuel pressure regulator placement:

vandelay industries

vandelay industries

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i heard/read that fuel pressure regulators should be located as close as possible to the carb. If so, why? And, how close is close? Is the firewall good? Fender? Or right on the intake?

a) If on the intake, then could i get some mounting ideas?

b) Also, could i get some good gauge ideas? i'd prefer one inside the cab(electric of course), but i'll mount a mechanical on the wiper cowl if necessary, because i don't have a whole lot of time.

c) The carb is a quadrajet, if that matters. Really, i'm just trying to make sure i don't go above 6.5lbs., but really 4 would be ok.

d) i heard/read return lines should be at least at big as the main line. Why? i think with most gm carbureted cars, the return line is smaller than the main.
 
The firewall is close enough for the regulator, racers typically mount them on the firewall, fenderwell or at the carb.

You can run a mechanical gauge inside, you just HAVE to run an isolator kit. I have this on my Blazer and LOVE it, it's a huge benefit when trying to diagnose issues.

As for return lines, a factory set up uses a smaller return. It really depends on the pump you're running. I run the factory tbi pump and lines with no issues.
 
I have run two fuel pressure regulators in my older carbed engines. One between the fuel pump and carb, and then one between my fuel tank and the fuel pump. This stopped fuel drain-back to the fuel tanks, and assured there was always fuel in lines between my fuel pump and carb, and the fuel tank and fuel pump.
 
I ran, what was it, one those cheap Mr gasket I think, fuel regulators. Mechanical pump to an edelbrock. Kept starving for fuel. Got rid of it and have been good since.
 
tenderfoot said:
Your running a mechanical fuel pump?
Click to expand...

No, electric which is advertised as putting out 4-7lbs, but i'm getting some soaking/leaking on the top gasket and other places on top. Also getting that vapor thing when shutting the engine off. Also, if i sit in a long traffic jam and it's hot outside, after we get moving sometimes the engine will totally bog and stall. After restarting and revving the engine, (sometimes have to repeat this process a few times) it will clear up.

i'm thinking the regulator, and checking the float level should solve these issues?
 
tenderfoot said:
I ran, what was it, one those cheap Mr gasket I think, fuel regulators. Mechanical pump to an edelbrock. Kept starving for fuel. Got rid of it and have been good since.
Click to expand...

I have run those cheap Mr. Gasket ones, and most of them functioned the way they where supposed to, but I have had a couple of bad ones. Only about 5-years ago I had one that was defective right out of the package. I exchanged it for another one, and that one worked. Those cheap Mr. Gasket ones are essentially only one-way check valves.
 
Just be sure that the regulator you get has a return port, not all do. Mine is a little different, I run a Barry Grant bypass valve with acts like a regulator but installs after the carb. My set up works really good with the factory tbi pump and qjet @ 5.5 psi.
 
I made a bracket and attached a pressure regulator to the alternator bracket. I put a chunk of rubber gasket material to act as a vibration isolator. While I don't think it is much, the alternator vibration doesn't seem to bother it.

There were not many regulators that got down into single digit pressure.

Long thread, I have details in here on the pressure regulator and why -- note that '74s do not have a return line yet. So there is a lot of fuel temp related discussion. I have been running this setup and it works. Also, after more than two days sitting, the fuel bowl dries up -- I didn't bother with an electric inline primer pump.

https://ck5.com/forums/threads/quadrajet-the-fuel-pump-fuel-bowl-and-accelerator-pump.317338/
 
forest said:
I made a bracket and attached a pressure regulator to the alternator bracket. I put a chunk of rubber gasket material to act as a vibration isolator. While I don't think it is much, the alternator vibration doesn't seem to bother it.

There were not many regulators that got down into single digit pressure.

Long thread, I have details in here on the pressure regulator and why -- note that '74s do not have a return line yet. So there is a lot of fuel temp related discussion. I have been running this setup and it works. Also, after more than two days sitting, the fuel bowl dries up -- I didn't bother with an electric inline primer pump.

https://ck5.com/forums/threads/quadrajet-the-fuel-pump-fuel-bowl-and-accelerator-pump.317338/
Click to expand...

Interesting write up. i have not been able to make it all the way through, but will definitely continue when there is more time.

UPDATE:
i was wrong----my elec pump puts out 4.25 to 6.25 lbs. according to specs. The quadrajet should be able to take 6.25 lbs.?

AND it happened again yesterday, and it wasn't THAT hot outside---maybe 68-69 degrees. i had run it pretty hard on the highway, then got off on an exit to a heavy populated area with lots of traffic lights. The engine temp did get a little higher than normal and as soon as we started moving----stalling. So, i have a hunch my problem is actually float level causing flooding and not necessarily too much fuel pressure or vapor lock---because if it were vapor lock, i wouldn't be able to start re-start the engine immediately?

i think it's better to do one thing at a time. My original plan was to check float AND add a regulator, but i think it's better to check float and test it first.

i am not automatically dismissing the possibilities of too much pressure, after all i need to verify fuel pressure with a gauge a not go by what the manufacturer says (it's a Facet Duralift btw) or vapor lock.
 
vandelay industries said:
My original plan was to check float AND add a regulator.
Click to expand...

I'd stay with that plan.

I wouldn't do anything until you have a pressure regulator. That is based on my before and after experience with the pressure regulator and from reading the QJet technical report's focus on pressure. A lot of nuanced issues went away once that regulator was on there.

Also, I went from a two-core to a three-core radiator and it was a big difference in cooling. That also helped. I used my orginal radiator and had it recored (it was $$ and I had to find a 90 year old guy that still did that).

Three things I wish I'd done when I first got my blazer: three-core radiator, pressure regulator, and tune the spark advance curve. All three might work for you too.

A high float isn't going to be solved either. I had a high float and ended up setting it lower than seemed necessary. It was a good move.

Edit I:
Also, before you tear apart your QJet (I've had mine apart so many time I could do it blindfold and drunk), contact Cliff and get his book -- he signed mine when I ordered it: How to Rebuild & Modify Rochester Quadrajet Carburetors (S-a Design) https://www.amazon.com/dp/1932494189/ref=cm_sw_r_cp_apa_i_F-L3Bb0T41S81

Edit II:
One of these spacers helped -- make sure it is phenolic https://goo.gl/images/GMFPCZ one like this is better but I can't find it for QJet https://goo.gl/images/egtB3D

You don't need read the rest of my other post, that is basically the cliff notes. I also put heat shielding between my headers and fuel line -- that was key, but I don't have a return line so idk how transferable that is.
 
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Specs for older vehicles with Quadrajet carbs in my old Motors manual states fuel pump pressure should be between 5 and 9 psi..

I tried one of those Purolator "dial" type pressure regulators on my '72 K5 once,it caused more problems than I had to begin with--it also started peeing gas on the intake and I was lucky the truck didn't burn to the ground..
 
I had Sean Murphy Induction build my qjet, they recommended ~5.5 psi.
 
I think most carbs need a "range" of pressure,not just one constant flow..some seem to work best with a steady regulated pressure,like when an electric pump is substituted--but many don't..

In a way a mechanical fuel pump is self regulating..hard to describe in words though..
Once the needle valve closes in the float chamber,pressure builds up in the fuel line leading to the carb..the fuel pump diaphragm has a spring under it that allows it to sort of "free wheel" until the engine uses up enough fuel to open the needle valve again..while it was closed,the fuel pump will go into the "free wheel" mode..

You can test this yourself on a pump off an engine by covering the fuel outlet and moving the rocker arm on the pump manually,you'll feel it go "slack"once it builds pressure up --when you release your finger, you'll feel the rocker arm start pumping the diaphragm again..

When your engine is idling or under a light load while cruising, 5.5 psi might be perfect..but floor it and kick in the secondaries,now you suddenly need more pressure and volume,and the pump will deliver full pressure...if its limited to a constant 5.5 psi,and a steady volume,it may not be enough for full load acceleration and high speeds..
 
vandelay industries said:
i heard/read that fuel pressure regulators should be located as close as possible to the carb. If so, why? And, how close is close? Is the firewall good? Fender? Or right on the intake?

a) If on the intake, then could i get some mounting ideas?

b) Also, could i get some good gauge ideas? i'd prefer one inside the cab(electric of course), but i'll mount a mechanical on the wiper cowl if necessary, because i don't have a whole lot of time.

c) The carb is a quadrajet, if that matters. Really, i'm just trying to make sure i don't go above 6.5lbs., but really 4 would be ok.

d) i heard/read return lines should be at least at big as the main line. Why? i think with most gm carbureted cars, the return line is smaller than the main.
Click to expand...
I don't believe this has been brought up. Is there a reason you can't run a mechanical pump?
 
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