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Electric fuel pump

Discussion in 'The Garage' started by mouse, Dec 20, 2003.

  1. mouse

    mouse 1/2 ton status

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    Well since buying the '77 K5 two weeks ago I've been working on getting it running better.

    After replacing all ignition components and fixing all vacuum leaks, the truck still has a mid throttle stumble, whether parked or driving. The carburator is a Carter AFB with an electric choke. My K20 has the very same one and it runs great.

    This one has the throttle shaft binding slightly, but the real concern is that the previous owner set up an electric fuel pump for it. On the carb itself, two fuel lines are run, one to the normal inlet, and another to the fitting at the top, middle of the carb.

    The fuel pump runs continuously, so the second line must be used as a return line. On my K20 the second inlet is plugged.

    I have never used an electric fuel pump on a SBC before, and wonder if this is the correct setup, or is this causing the float valve to stay open and cause the problems that I have. If the carb is shot, rather than rebuild I might steal the K20's or buy a new one....any thoughts? /forums/images/graemlins/k5.gif
     
  2. CyberSniper

    CyberSniper 1/2 ton status Premium Member

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    What kind of electric fuel pump is it? My Carter street/strip pump doesn't require a return line. It also only produces 4.5psi.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Fitting at the top, middle of carb. Is that the large (5/16" or so?) fitting angling off towards the drivers side?

    Either way there should be fuel only going into the main gas port. The large one up top (if present) is EVAP, and anything else is supposed to be vacuum. Could be a ported vacuum fitting that is sucking gas when it is uncovered at part throttle.

    Unless this is some fuel pump setup I've never seen or heard of, there should be one fuel line running to the carb, period.
     
  4. mouse

    mouse 1/2 ton status

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    The fitting in the middle of the carb is on top, like the fuel feed, and is on the passenger side. Like I said earlier, its plugged on my other truck. That port is attached to a 3/8" fuel line that runs down to the frame on the passenger side, to what I assume is the fuel tank. I guess I'll have to track it down tomorrow. The fuel pump is mounted on the passenger side, behind the rear leaf shackle, and appears to be a holley fuel pump. I have to clean it to see what it is. It "clicks" while pumping, and has a fuel filter between it and the tank. It always runs, which I assume is the way it is designed to. I have a fuel pressure/vacuum gage I could hook up if this kind is adjustable. But I thought fuel pressure regulators are a separate component.....
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I dunno what your truck had stock emissions wise, perhaps it is the fuel tank vapor line (again, if your truck ever had that) and thats what the PO hooked up to the carb port.

    You are right though, track the hose down, that might give you all the info you need.
     
  6. A&P

    A&P Registered Member

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    I don't know the history of carbs that GM used, but that is the same carb that came stock on the dodge trucks around 83'. My bro had that setup on his Ramcharger, and that other line is a fuel return line. If you have another of the same carb, just swap it to the blazer and see if it fixes the problem. If so, just get a remaned q-jet, and don't worry about the return. Just keep using the same config. That's what I'd do anyways. If the pump has a red label on it, you're good to go. My buddy runs a holley red with a q-jet, and it works perfectly. Just eliminate that the carb is the problem or not. Start basic, and rule out the problems. Just my $.02
     
  7. mouse

    mouse 1/2 ton status

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    The pump reads 5 psi on it with no other tags. The fuel lines from the carb both run down to the frame, to hard lines, which run towards the rear of the truck.
     

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