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Thread: Optimal Fuel Pressure (Carburetor)

  1. #1
    The man, the myth, the legend global warmer's Avatar
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    Optimal Fuel Pressure (Carburetor)

    I have a 600 cfm Edelbrock carburetor on a 350. Does anyone know the ideal fuel pressure? I believe I'm getting too much fuel.

    I've been at it for about 2 hours now, and so far nothing has gone right today...OY!

    I'm thinking the regulator won't allow enough fuel, the new steel brake lines won't thread, and one of the lines is too short...gonna be a long day, but I guess it beats punching the clock!

    GW

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    chevrolet connoisseur The man, the myth, the legend b-lazer's Avatar
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    Should be 5.5 lbs according to edelbrock. And at first you say your getting to much fuel and then you say you think your regulator isn't allowing enough.which one?..getting alot of black smoke out the pipes?..good spot to start Is back your mixture screws all the way in till they stop (don't force or crank them tight)then back them out a 1 or maybe 1.5 turns



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  3. #3
    The man, the myth, the legend global warmer's Avatar
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    sorry I was unclear ::

    the regulator isn't in yet...the packaging reads "up to 5.5 psi". The electric pump pushes 5-9 psi...its not adjustable so I guess its pushing 9 psi and can safely be brought down to 5 psi (w/ regulator) without damaging the pump <--- pure guess.

    When the truck runs with the unregulated pump it smells awful...overwhelming exhaust with a hint of musky unburned fuel...and that's pretty bad since I always run with a safari top.

    Across the internet I've seen that SBC mechanical pumps run anywhere from 6-9 psi, that's why I didn't regulate it the first time...Max 9 psi...sbc upto 9 psi...figured it as OK...WRONG!

    My regulator adjusts from 1-5.5 psi...left me wondering if I need a regulator that will allow more psi...

    I've decided since my day has been so challenging, I'm going to the liquor store, then putting the 5.5 psi regulator on, then I'll see where we are...

    Thanks for the quick answer...I'll let you know how it turns out-

    GW

  4. #4
    The man, the myth, the legend global warmer's Avatar
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    Incidentally, it bogs when I get on it, and once in a while the carb will pop off (backfire in the carb...not the .308 in the neighborhood kind...lol)

  5. #5
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    How fresh is your carb? Might be time for a good cleaning.

  6. #6
    The man, the myth, the legend global warmer's Avatar
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    You might be on to something 70... Here's the dealio...

    installed everything in line...filter->pump->regulator->gauge->carb...

    turns out when the regulator is on the truck won't stay running, the gauge reads ~0psi...

    remove the regulator and the gauge reads ~7psi and the truck "runs"...

    thus, the brand new regulator is a POS, the pump is moving too much fuel, and I just need to get a whole new filter->pump->regulator->gauge setup...unless someone has a better solution???

    While I'm at it, I think I'll follow 70's advice and clean the carb...the PO took great care of my rig, but its been awhile now

    On a lighter note... I have 4.11 in the rear and 4.10 in the front...is this normal? I have pics!

    Thanks for all the help-
    GW

  7. #7
    The man, the myth, the legend global warmer's Avatar
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    Quote Originally Posted by 70-K5 View Post
    How fresh is your carb? Might be time for a good cleaning.
    I was all over the place today...

    I exchanged the POS fuel pressure regulator for a new POS fuel pressure regulator...

    Here's what I know ::
    1) without regulator fuel is steady @ 7psi
    2) with first POS regulator fuel is steady at 0 psi...yeah zero
    3) with second POS regulator fuel would not get above 3.5 psi

    so a regulator that advertises 1 to 5.5 psi appears to max out at about 3.5 psi...nice

    I also found that the carb at idle is pulling ~14 in Hg at the constant port, but I don't really know that the vacuum means anything until I get the pressure stable @ 5.5 psi.

    I did turn the mix screws in fully, then backed them out about 1.5 turns it ran a little rough...but I understand a cheap way to get tunes right is to tinker with the mix until I achieve max vacuum...don't know about that.

    Anyhow, once I get the fuel pressure stable I'll put in a carb kit, then hit you up about how to get that rig tunified...

    GW

  8. #8
    Yawnnn!....... Lets hit the woods. Chief Hunglikmule Just-speed's Avatar
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    Quote Originally Posted by global warmer View Post
    I was all over the place today...

    I exchanged the POS fuel pressure regulator for a new POS fuel pressure regulator...

    Here's what I know ::
    1) without regulator fuel is steady @ 7psi
    2) with first POS regulator fuel is steady at 0 psi...yeah zero
    3) with second POS regulator fuel would not get above 3.5 psi

    so a regulator that advertises 1 to 5.5 psi appears to max out at about 3.5 psi...nice

    I also found that the carb at idle is pulling ~14 in Hg at the constant port, but I don't really know that the vacuum means anything until I get the pressure stable @ 5.5 psi.

    I did turn the mix screws in fully, then backed them out about 1.5 turns it ran a little rough...but I understand a cheap way to get tunes right is to tinker with the mix until I achieve max vacuum...don't know about that.

    Anyhow, once I get the fuel pressure stable I'll put in a carb kit, then hit you up about how to get that rig tunified...

    GW
    Very good learning. You did pick up some great tips. Keep in mind your idle mixture screws only affect idle. (Idle Circuit). A good starting point is 2 and 1/2 turns out. Yes you want max Hg at idle. 14 is not bad at all. Between 15 and 17 is what I would look for.

    As for the fuel issue. Your carb is said to be able to handle 5.5 psi of fuel max. You are getting mixed results. Let me ask. Have you checked volume? Perhaps you should take a look at the volume of fuel being pumped before moving forward. Might find your not getting enough volume.
    Just-Speed (Mike)
    85 K5 383,4l80(manual valve body),np241,D60 front,Corp 14B ff rear. (5.13 gear)

    Just-speed@earthlink.net
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  9. #9
    Yawnnn!....... Lets hit the woods. Chief Hunglikmule Just-speed's Avatar
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    Let me just add. You can get 3.5psi with 1 gallon an hour being pumped just as you could with 50gpi pumped. Your goal is to control the right volume of fuel at correct pressure.
    Just-Speed (Mike)
    85 K5 383,4l80(manual valve body),np241,D60 front,Corp 14B ff rear. (5.13 gear)

    Just-speed@earthlink.net
    Cell 352-454-1426





  10. #10
    The man, the myth, the legend global warmer's Avatar
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    Quote Originally Posted by Just-speed View Post
    Let me just add. You can get 3.5psi with 1 gallon an hour being pumped just as you could with 50gpi pumped. Your goal is to control the right volume of fuel at correct pressure.
    How is volume measured? I'm thinking flow rate, but that's variant with respect to engine demand.

    While I was hunting the failed component, ultimately the first POS regulator, I had the fuel line routed into a coffee can, I could hear the fuel hitting it from inside the cab...the coffee can was in the engine compartment...seemed like it was moving alot of fuel, but as you point out- we better make sure

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