Fuel Pressure Regulator?

[mas84_720]

I had put a inline gauge on the fuel line and discovered my fuel pressure was barely reaching 1.5psi, so i bypassed the return and now im getting a steady 3.5psi... at idle. As soon as i press the throttle it drops and bounces around 1-2psi, this is sitting in driveway with no load.

 

I have already replaced the fuel filter and it is fresh good quality gas. All fuel lines are new except the hard line running along the frame from tank to under hood(which is verified clear).

 

Im thinking weak pump (which is an aftermarket Airtex 2.5-4psi pump). Im wanting to redo the fuel delivery with a stronger pump and regulator. My question is how important is the return line? The only regulators i can find with return line ports are for higher pressure. Holley 12-804 is a 1-4 psi regulator but no return, Holley makes a 12-803BP which is a bypass with return line but the 803 is for 4.5-9psi.

 

Will it be ok to run it without the return with a regulator?

 

Oh i have a Weber 32/36 carb.

[TENDRIL]

im pretty sure you 32/36 will not run out of gas even with only  1.5-2 lbs of pressure .. at least its never happened to my 32/36 with a stock/aftermarket pump rated for 2-3 lbs

 

 

could be wrong tho 

 

are you having a certain problem that is worrying you or is it more a peace of mind thing? 

[datzenmike]

If it runs problem free just leave it. Maybe the gauge is wrong.

 

 

The return line should have a small restriction in it so the pump has to push against it and build pressure. Someone took it out and connected the fuel line to the carb without it.

[Ranman72]

my gauge which is a 40 dollar liquid filled and a brand new Nissan pump sometimes reads  0 and I have never starved from fuel delivery no mater how hard I drive it 

if it is running ok dont worry about it probably a faulty gauge 

[mas84_720]

Its not running ok though. Stumbles under load, going up hill, or anything past 1/2 throttle.

 

The restriction in the stock return line is not there, it was just wide open. I actually said the first part a bit wrong, with the return line and gauge inline it was reading 0, with return line and gauge plugging the end that went to carb it read 1.5, removed return line and now gauge inline reads 3.5.

 

This has been an on going proccess to get the truck running smoothly, I have just been going over everything and when i see something that looks abnormal i try to fix it right or above original.

[datzenmike]

The L20B has a return line fuel rail and at the end it is closed off but for a small pin hole. This allos a small amount of fuel cool gas from the tank circulating past the carb. The 720 would normally have this between the manifold runners between the carb and the valve cover. This is where the stock 720 fuel line comes up from under the manifold to feed the carb. Look and see if it's still there. You could cut the restriction off and simply gear clamp it in line on the return.

[mas84_720]

Here is the fuel line that was attached to the intake manifold going to the carb.

 

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Can i utilize the return port off the carb here?

 

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And could my problem actually be fuel flooding instead of starvation because of the no return line?

[datzenmike]

 

Is there any restriction in those lines? I figured that was where it was.

Here's the L20B restriction...

[mas84_720]

The only thing i noticed was that the return line was a slightly smaller diameter, but it looks wide open from what i can see.

[datzenmike]

Returns are usually larger

[Billychar]

most likely an earth problem where the earth wires in the loom are connected by a ring of metal crimped around the wires at a junction. Fuel is the least likely cause of the symptoms described. It is a problem listed in factory bulletin to the agencies. It can also cause erratic idle performance and other poor performance and running conditions. Essentially a fault when resistance increases in the low tension circuit of ignition system. A problem in D21s' also.  Figured I'd post a reply to this OLD post for ruture reference of those who may be facing the same problem.