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Thread: Pressure Regulator Question

  1. #1

    Default Pressure Regulator Question

    I've got a Holley 750 double pumper carb with a 110 GPH "Blue" fuel pump and a 12-803BP regulator. My problem is, when I go out in the morning while the engine is cold, turn on the key to get the fuel pump running, my fuel pressure is 7 PSI. Just where I want it. I start the engine and fuel pressure goes to 10.5 PSI. Way to high for me. I checked this morning, same problem. Turned the engine off (although I didn't run to get up to temp this time) pressure is 7 PSI. Started again, 10.5 PSI.

    I have the fuel coming in from the rear of the carb (dual line), regulator is just before the first bowl, fuel gauge is at end of fuel line. If you guys have and ideas on what's going on I'm all ears. Here is a picture. Thanks, Carl


  2. #2
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    The fuel pressure regulator should be adjusted with the engine running.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #3

    Default

    Thanks for the reply Danny,

    I know that the adjustments should be made while running, I was just trying different things.
    It's just that with the engine not running, and the fuel pump on I get 7 PSI. Start the engine it goes to 10.5 PSI. That in itself throws me for a loop. I have tried adjusting pressure, both with the engine running and not running (fuel pump on). Here's what I've done so far.

    I took the fuel regulator apart, it was pretty clean! I put it back together, blew into the end the fuel comes in, blocked off the exit and air came out of the return port. I even tried adjusting the screw while under pressure. It seemed to work.
    I then took a compressor and blew air back through the return line, and could hear air coming out of the tank. (So I think that's not clogged.)
    I looked at the float levels, first, with the engine not running. But fuel pump running, fuel level just trickled out of the bottom of the sight hole.
    Started the engine and looked at the fuel level at the sight plug, and it was just trickling out just as before, only at 10.5 PSI at the gauge.
    I'm going to go get another gauge and see if mine is bad to see if that's the problem.

    Are you saying the pressure regulator should be adjusted with the engine running, at idle or above idle? I've tried at idle, and the gauge never moved no matter how far the adjustment screw was moved. I'm about frustrated!! Thanks for your help. (Oh, and I like your signature.)

    Carl

  4. #4

    Default

    Quote Originally Posted by minendrews68 View Post
    I know that the adjustments should be made while running, I was just trying different things.
    It's just that with the engine not running, and the fuel pump on I get 7 PSI. Start the engine it goes to 10.5 PSI. That in itself throws me for a loop. I have tried adjusting pressure, both with the engine running and not running (fuel pump on). Here's what I've done so far.

    I took the fuel regulator apart, it was pretty clean! I put it back together, blew into the end the fuel comes in, blocked off the exit and air came out of the return port. I even tried adjusting the screw while under pressure. It seemed to work.
    I then took a compressor and blew air back through the return line, and could hear air coming out of the tank. (So I think that's not clogged.)
    I looked at the float levels, first, with the engine not running. But fuel pump running, fuel level just trickled out of the bottom of the sight hole.
    Started the engine and looked at the fuel level at the sight plug, and it was just trickling out just as before, only at 10.5 PSI at the gauge.
    I'm going to go get another gauge and see if mine is bad to see if that's the problem.

    Are you saying the pressure regulator should be adjusted with the engine running, at idle or above idle? I've tried at idle, and the gauge never moved no matter how far the adjustment screw was moved. I'm about frustrated!! Thanks for your help.
    The reason you adjust with car running is VOLTAGE. With car off your voltage is around 12V. With car running, your voltage should be around 14.3V. The higher voltage causes the pump to run faster therefore causing a higher fuel pressure. Adjusting fuel pressure at idle should be fine. You should be turning the adjustment screw clockwise, I believe, to reduce pressure. 10.5 PSI might be enough pressure to not allow your needle/seat to close.

  5. #5

    Default

    The voltage thing makes perfect sense. You think turning adjustment screw clockwise reduces pressure? I'll look at that in the morning. Still don't know why when I adjust the regulator there isn't any change in pressure on the gauge. I was thinking the 10.5 PSI would've been enough pressure to cause problems too. With the engine running and the plug out of the sight hole, the gas just seeped out. I'm at a loss.

  6. #6
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    Quote Originally Posted by 69cam View Post
    You should be turning the adjustment screw clockwise, I believe, to reduce pressure.
    No, it's the opposite way.

    Quote Originally Posted by minendrews68 View Post
    You think turning adjustment screw clockwise reduces pressure?
    Loosening the regulator lock nut and turning the adjustment screw clockwise, increases the
    fuel pressure. Decrease fuel pressure by turning the adjustment screw counter-clockwise.
    http://documents.holley.com/199r7914-3rev6.pdf (Holley 12-803BP Fuel Pressure Regulator - Step 6, Page 3)

    Quote Originally Posted by minendrews68 View Post
    The voltage thing makes perfect sense.
    Yes, because it's an electric fuel pump. The fuel pump volume output is directly relative to voltage. 12.0V-14.3V makes
    a significant difference. Although if I remember correctly, this shouldn't matter with a bypass style fuel pressure regulator.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  7. #7

    Default

    Thus why they call it a regulator, huh? LOL!

    I did take the bypass loose from the regulator, and blew 110 PSI air through it. I'm wondering if, maybe the hose is collapsed at the tank end and the 100+ pressure opened it up. The braided hose at the carb end has a Teflon lining, the other end has a rubber hose. My only thoughts there are, why not the supply line too. I'm going to try to run another bypass out of the bottom of the regulator to a gas can, and see what happens. I bought another fuel pressure gauge, and I'm going to try that too. If you guys come up with another idea I'm here, and if any of these work I'll let everyone know. Thanks for the help so far.

  8. #8

    Default

    OK, these are my thoughts now. After taking my regulator apart again, I still find nothing I can see that's wrong. I took my air hose and blew air through the bypass again, it seems like it takes a good deal more than 10 PSI to blow through to the tank. I'm thinking there's got to be somewhat of a blockage there, even though increased pressure will go through. I'm thinking if it takes more than 10 PSI to get the bypass to work, it won't until I find the blockage. I'm taking the car to a friends garage Monday to put it on a lift, and see if my thoughts are right. I'll let everyone know what I find out.

  9. #9
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    Quote Originally Posted by minendrews68 View Post
    I took my air hose and blew air through the bypass again, it seems like it takes a good deal more than 10 PSI to blow through to the tank. I'm thinking there's got to be somewhat of a blockage there, even though increased pressure will go through. I'm thinking if it takes more than 10 PSI to get the bypass to work, it won't until I find the blockage.
    So temporarily substitute that bypass hose with a piece of rubber hose into a bucket. Then see if the fuel pressure regulator will adjust.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  10. #10

    Default

    I can do that.

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