fuel pressure won't lower / pmo with webers

[jimtweet]

I just developed a weird problem. I installed new PMO regulator and pierburg pump. Fuel pressure keeps shooting up to 4.5+ on PMO. I tried backing adjustment screw out all the way and nothing.

[mreid]

Do you have a return line?

Is this a new installation or did it work fine and then suddenly start doing this? Sometimes a piece of debris like a. Rubber hose shaving gets caught in the regulator. With the pump running, give it a couple light whacks with a screwdriver handle. If that doesn't work, remove it and blow it out with compressed air.

[jimtweet]

New installation but was running perfectly fine for two weeks

[jimtweet]

No return line

[gumba]

The regulator reduces the pressure by controlling the flow through the return line back to the tank.

[mreid]

The PMO regulator is not meant to be used as a deadhead. The pressure will be erratic. Recommend you install a return line.

[jimtweet]

I have seen a million of these setups with no return lines.

[boyt911sc]

Originally Posted by jimtweet

No return line

Where do you expect the excess fuel to go if you don't have any return line? Are you certain your set-up does not have any return line? The PMO regulators deliver the adjusted (controlled) fuel pressure to the carburators and the excess fuel is recycled back to the source (tank). Keep us posted. Thanks.

Tony

[jimtweet]

I was told that with the low pressure pierburg pump I didn't need one. I am apparently wrong. Is there a return bung or inlet in my fuel tank? Is a 1974 that had a 2.7 Cis. Now a 1982sc 3.0

[mreid]

Yes there is mine is a 74 with PMOs. The CIS requires a return line. The fuel pump mounts to a bracket next to the rear driver side sway bar mount. Where the supply line exits the rear of the tunnel, there is a return line next to it.

[joefrantz]

You don't need a return line. Carbed 911's were all deadhead from the factory.

You may need a different regulator if the PMO requires a return.

I'm not familiar with PMO regulators, but from your picture it looks like one of the ports on the left side is capped. Is that an adaptation for use without the return line? Does PMO support use of the regulator in that way?

My pierburg pump puts out 7psi and I regulate it down to 3.5 with a holley regulator. My pump is
on the front crossmember.

Do you know the output rating of your pump? When I bought mine several years ago they were available in 5 or 7 psi. At that time the 7 was recommended for front mount (by PMO) because of pressure drop over the distance to the engine.

If you have a seven on the rear mount, the regulator, as configured, may not be able to drop the pressure that much.

[LJ851]

If you don't want to use a return line, get one of these regulators.

Holley Performance Products Two Port 1-4 PSI, Chrome*12-804


Avoid the chrome round ones with the dial like the plague.