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12-840 Fuel Pressure Regulator

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  • 12-840 Fuel Pressure Regulator

    New Member here. Thanks for having me. I did a little searching and found I was having a similar issue as another member with my fuel pressure regulator. However, his is a different part number so I didn't want to hijack his thread. So I'm using the 12-840 regulator to try reducing fuel pressure to my Holley 4150. I'm also using a 26-500 fuel pressure gauge at the port connection on the regulator. I've found that adjusting the regulator provides no change in pressure. All the way closed, all the way open, same pressure. First I thought the gauge was faulty so I connected my fuel pressure test gauge and got the same results, no change in pressure. I then ordered another 12-840 regulator and installed it. Same results, no change in pressure regardless of where the adjustment screw is. Anyone have any ideas what's going on here? Kind Regards, Patrick Stapler

  • #2
    Can you supply some info please Patrick? Your whole fuel system, tank pickup tube size, filters, fuel pump, line size, etc? And you have this regulator in series between the fuel pump and carburetor, as a "deadhead" regulator, and NOT as a "bypass" regulator back to the tank? Gary
    Regards, Gary


    • #3
      Yes. ATI Fuel cell with 1/2 pickup tubes.
      1/2 line from fuel cell to remote mount canister filter.
      1/2 line from filter to Holley 12-289-20 pump.
      1/2 line from pump to regulator.
      3/8 line from regulator to Earls inline filter.
      3/8 line from inline filter to Holley 4150 650DP.

      I did speak with Sean Murphy of SMI Carburetors, the builder of my carb and he had me run a fuel system test.

      I disconnected the line from the regulator to the carb and placed it in a jug. Ran the car for 30 seconds. It pumped out approximately 1-1/4 quarts. He said it needs to be about one gallon/min or two quarts/30 seconds. He also said too many 90 fittings might cause this.

      So my current plan is to replace the two 90 fittings from the fuel cell to the rear bulkhead with straight fittings. This will equate to roughly 24% volume added back to the flow.

      Secondly, I was wondering if I should connect the second pickup line at the fuel cell (it has left & right pickups) and tee it into the other pickup line prior to the bulkhead. However, I wondered if that might cause turbulence at the tee which would minimize flow yet again. Kind Regards, Patrick Stapler
      Last edited by PatrickStapler; 04-11-2021, 07:07 AM.


      • #4
        What filter are you using before the pump?
        Can you show some pics of your system?
        And what's the fuel pressure doing, too high, or too low?
        And you did tell Sean you're using a mechanical pump, since a volume test of 30 seconds at idle doesn't show what the pump CAN put out, in comparison to an electric pump test.
        And yes, I would remove any cast 90 (without a curved bend).
        Last edited by Gaz64; 04-11-2021, 07:09 PM.
        Regards, Gary


        • #5
          I tried to upload pics, but the forum wouldn’t allow.
          I run a WIX remote fuel filter and element.
          Pressure has been checked with a Holley gauge and separate fuel pressure test gauge at right at 6 psi regardless of the regulator setting.
          Yes, Sean knows I’m running a mechanical pump.
          I questioned this about the 90s as well. All of my fittings are curved bend 90s. None of them are hard dead ends.
          The pump is rated at 170 GPH.


          • #6
            The gauge is mounted on the regulator outlet, on the line between the regulator and the carburetor?
            Regards, Gary


            • #7
              In both cases, the gauge was mounted on the port connection of the regulator.


              • #8
                That's interesting issue you have there Patrick.
                The pump itself would be about 7.5 - 8 psi.
                So winding the regulator adjustment in, should max out at the pump spring pressure.
                Winding the screw out, you should be able to get 4.5 psi minimum, as stated by Holley.
                Have you thought about running an electric pump at the rear, instead of an engine driven mechanical pump?
                Regards, Gary


                • #9
                  I thought so as well. No I have not considered an electric pump. Vintage race rules don’t permit it.