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Minimum Fuel Pressure?

Discussion in 'The Garage' started by Hossbaby50, Feb 8, 2003.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    I was wondering what the minimum fuel pressure was for a carb 350. I recently had a fuel pump go out, and I replaced it. I am also thinking or running an electrical pump in line too (on a dash mounted switch), but only use it should something happen to the mech pump again. I saw a universal inline pump on the Napa site, and it is rated at 4-6 psi. Most mechs run around 8 right. Would 4-6 be enough to run the carb? Also, if the elec. pump was inline could the mech. pump suck the gas threw it or would I have to route around the elec. pump? I want to plumb them both in the line at the same time and only use one at a time, is this possible?

    Motor is a stockish 350 with 4brl Qjet.

    Thanks
    Harley
     
  2. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    Never tried it but I wouldn't pull the fuel through a elec. pump. My carb says they want 5 psi and that is where it is set. Have you thought about a duel tank switch? That way you could switch from one to the other. Good luck Harley
    Dave
     
  3. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    there is no minimum pressure for a carb, it just needs fuel in it so amybe like 1 psi to get up to the carb. I think that the mechanical pump is like4 to 6 psi. im not sure if the mechanical pump would pull the gas through the electric pump. my dad had a mechanical pump go out and he put a gas can up side down on the hood and run the washer hose from the vent on the gas can to the carb and drove home.
     
  4. Hossbaby50

    Hossbaby50 3/4 ton status

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    Here is another question to add on. Can an elec. pump push fuel threw a mech pump?
     
  5. schmuck

    schmuck 1/2 ton status

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    i belive the standard for a mech pump is about 5psi
     
  6. m j

    m j 1/2 ton status

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    you need a restriction to create pressure.
    the only restriction is the needle&seat.
    so your mech will hold whatever the needle and seat will.
    PSI is not imortant, volume is.
    the work is not worth it for your ap IMO
     
  7. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I was having fuel supply problems(due to a worn cam lobe in my 305) so I removed the mech. pump and went with an electric pump. That was over 9 years ago. I haven't had a problem since. The cool thing about my electric pump is that it's wired to come on in the Aux. position- before I start the truck, I let the pump run for a second or two to make sure the carb is full of fuel.

    Last time I checked, my electric pump was pushing about 4 PSI up to the carb.

    I know guys that run an electric pump AND the mechanical pump. I'm not sure if there's any benefit to doing that.
     
  8. ntsqd

    ntsqd 1/2 ton status

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    I run an electric and a mech. pump on the same vehicle, though it is not a GM product. The electric is on there for back-up and to prime the carb since that vehicle sits for long periods. So it can push thru the mech. pump. I suspect that most mech pumps can be pushed thru since their check valves are intended to have fuel flowing in that direction.
    Some elec. pumps can be pulled thru, others can not. Holley Blue's & Red's are examples of those that can not. The Facet impulse pumps are some that can.

    Fuel pressure requirements vary with the specific carb. Holleys tend to want around 8 psi on the street. Never have run one off road so I don't know if it would need to change.
    Q-Jets seem to like a little less than that, say 4-6 psi.
    Webers rarely are happy with more than 4 psi.
     

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