bwh69s

I recently replaced my worn out 350 with a 455 in my 69 Cutlass. It runs great. I wanted to make sure I was getting a consistent 6 PSI fuel pressure to the carb, so I installed a mechanical fuel pressure regulator. After installation and leak check, I started adjusting the regulator. I initially got good response on my guage and increased pressure from 3 to 5 fairly quickly. But, then the guage stopped moving. No matter how much adjustment I made, it would not increase fuel press. I backed the adjustment off until I started getting a reduction in fuel press and locked the adjustment screw. I came out a couple days later, backed out the adjustment screw and started all over, but again no more than 5 psi. I replaced my guage with an Aeromotive guage just in case that was the issue but no change. Also, once I turn the engine off, the fuel pressure will gradually drop to zero by the next day. I just started the car today and noticed that i have air bubbles forming at the intake side of my filter between the pump and the pressure regulator. I recently changed out all my flex hose between the tank and the pump so I know I'm not pulling air thru a rotted piece of hose. The fuel pump is brand new. Any ideas on how to get 6 psi?

Schurkey

1. Are you using a liquid-filled gauge? Did you "burp" the gauge at the rubber seal each time, before taking your readings?
2. Fuel pump weak? The mechanical fuel pumps are limited by the spring pressure; if the internal spring is weak...so is the fuel pressure. Regulators can reduce pressure, they can't increase it above what the pump provides.

matt69olds

What kind of pump are you using? I can tell you from personal experience the AirTex 40367 pump is capable of keeping up with a stout 455. The pumps are replacement for the Toronado and 455 performance pump. Last one I bought I got from advance Auto for about 40 bucks.

The other option is the RobbMc pump. It’s a much bigger pump than any other mechanical pump so it may be a tight fit depending on your accessories.

The other options are electric pumps.

shiftbyear

Is it a liquid filled gauge?

bwh69s

Schurkey, yes I have a liquid filled guage and I did burp it before taking the reading ... well, I did that when I finally figured out that I was supposed to anyway

I didn't think about the regulator only regulating vice increasing pressure, thanks for that. So, I'll check the fuel pump next I guess.

bwh69s

Thanks for the tip on the Air Tex pump matt69olds, I'll see if I can find one.

bwh69s

shftbyear, thanks for the video link. It's a good one. I actually bought the very Aeromotive guage that the guy recommended in the video.

Ozzie

The car should have a saran fuel filter on the pickup in the tank. Be sure that it is not congested.

OLDSter Ralph

Why do you think you need more than 5 PSI ? If you are getting enough fuel to feed the engine, 5 PSI should be fine.
..........Just my two cents worth.

gs72

I was thinking the same thing. With carburetors it's more about volume of fuel than pressure. sure you need a little pressure to lift the needle off of the seat, but the goal of the fuel pump is to be capable of delivering more fuel flow than the engine needs.
As long as the pump can deliver 1/2 a pint or more in 15 seconds you are golden.

Sugar Bear

If your car runs well and the pump is a consistent 5 PSI that is a win. Additional pressure may cause flooding by pushing the needle valve away from the seat.

Ride on and good luck!!!

Ozzie

I don't have the 1968 or 1969 Chassis Service Manuals. The one for 1967 says 5 to 7 PSI is normal for the V-8 engines. The one for 1970 says 5 to 6 PSI is normal for the V-8 engines.