question on '84 F-150 fuel system

Discussion in 'Shop Talk' started by tamarackreg, Jan 14, 2007.

  1. tamarackreg

    tamarackreg Well-Known Member

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    When the truck is shut off over night the fuel drains back to the tank. This truck has a 351 motor w/ a Holly 4 brl carb and mechanical fuel pump. I assume that there should be a check of some kind in the system to prevent this. Can anyone tell me a) if I'm right, b) where it is?
    Thanks for any and all responses.
     
  2. agmantoo

    agmantoo agmantoo Supporter

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    I cannot respond to your specific vehicle but I can tell you that such drain back issues often are a result of air leaking into the fuel lines. Loose fittings , cracked lines and improper seated fuel filters are the typical cause. Possibly even a perforated disphram in the fuel pump. I would look for wet areas in the fuel system.
     

  3. Beeman

    Beeman Well-Known Member

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    There is no actual check valve in a carb system. There are check balls inside the mechanical fuel pump but they are only for when the pump is working. A carb has float bowls which contain a resevoir of gas so the engine has gas immediately upon cranking to start. If the carb is physically leaking, which on a Holley would be externally and visible, that is all that would cause no gas for start up. The gas can not physically drain back to the tank out of the carb bowl. I also seriously doubt the gas is evaporating over nite. Ther should be a plug on the side of the float bowls which is used to adjust float height, possibly the floats are set too low?
     
  4. moopups

    moopups In Remembrance

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    Make sure the float bowl air vent is open, if its clogged the pressure of the compressed air will push the gas back down and then up into the jets. So the gas evaporates by morning.
     
  5. tamarackreg

    tamarackreg Well-Known Member

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    Thanks for the replies. This afternoon I had no gas in the carb after trying to start it for several minutes. I then pressurized the gas tank w/ air and that got gas to the carb. After a short and almost successful attempt at starting I checked agian and there was no gas. Pulled the fuel line and cranked the motor - no gas. I'll get a fuel pump on the way home from work tomorrow.
     
  6. pcwerk

    pcwerk Well-Known Member Supporter

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    I have a Haynes manual for the 80-96 Broncos and Pick-ups. Sell it for
    $5.00 plus whatever shipping is if your interested.
    james
     
  7. tamarackreg

    tamarackreg Well-Known Member

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    Thanks for the offer pcwerk but I'm planning on selling the truck as soon as winter is over. Put the new fuel pump on today and still no gas! The lines are all open so I guess I'll be putting an electric pump on this weekend. Thanks agian pcwerk and good luck.
     
  8. Beeman

    Beeman Well-Known Member

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    Before putting on an electric pump I would check the rubber lines for cracks and possibly the sock/filter in the tank for being plugged. I have been fooled before and changed a pump for no reason. I check the mechanical pump for vacum and pressure with a gauge. If you have a crack in a rubber line between the tank and the pump it would be like having a hole in your straw, you can't suck anything up. If the sock is clogged it would plug the line and prevent any fuel from being drawn up. You can possibly blow back in the line and either clear the sock temporaraily or blow it compltely off of the pickup tube. Either way be sure you have a good fuel filter after the pump.


    You don't have any fuel filter before the pump do you?
     
  9. fixer1958

    fixer1958 None of the Above

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    What Beeman said, and have several filters on hand for the future.