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Fuel line from carb loses prime

Discussion in 'The Engine Bay' started by zackmoxley, Sep 17, 2016.

  1. zackmoxley

    zackmoxley Registered Member Premium Member

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    I have a 1979 blazer. When its warm and it sits for more that 10 min, the fuel in the fuel line drains back into the tank making it difficult to start. It has a new fuel pump. What could be causing this?
    Thanks.
     
  2. bent72

    bent72 Desert Solitaire Premium Member GMOTM Winner

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    Line is not tight or hole in the line.

    Mine did this early this year, the split was back by the tank
     
  3. zackmoxley

    zackmoxley Registered Member Premium Member

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    Was your fuel leaking out onto the ground?
     
  4. blazer74

    blazer74 Member Premium Member

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    10 minutes hard to start. Could be flooding instead.
    Too much fuel psi from pump overcomes needle and seat and floods.
    Regardless even with pump drain back the carb should hold fuel for a lot more than 10 minutes.
    Do you have to hold the pedal down to get a start after 10 minutes but ok start after a couple of hours?
     
  5. zackmoxley

    zackmoxley Registered Member Premium Member

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    It seems to only do it when its warm. Once it cools a bit, it starts normally. i have a glass fuel filter and a pressure gauge. The gauge bleeds to zero and you can see air bubbles replacing the fuel in the filter
     
  6. rpcraft

    rpcraft 1/2 ton status Premium Member

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    Sounds weird but you may need to check the vent on your tank and make sure it is venting properly. The only real reason it should suck back so far in the line is if the tank is pulling a vacuum because the fuel pump is not that much higher than the opening of the fuel tank in them.
     
  7. zackmoxley

    zackmoxley Registered Member Premium Member

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    Is the cap suppose to vent or is there a separate vent i should check and where would it be?
     
  8. riflerk20

    riflerk20 1/2 ton status Premium Member

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    Vapor lock? Are the fuel lines too close to the exhaust or anything else that might get hot ?
     
  9. rpcraft

    rpcraft 1/2 ton status Premium Member

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    There is a vent line that runs from the tank along side the fill tube. Might be rust or some kind of grunge in there or also something on the openings in the sending unit.
     
  10. zackmoxley

    zackmoxley Registered Member Premium Member

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    The vent tube empties into the filler neck. If the gas cap is not venting, the tank wont vent properly right?
     
  11. blazer74

    blazer74 Member Premium Member

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    Next time u drive it and park warm watch your in line psi gauge and see if it goes up as the fuel in the line heat soaks and expands, if the needle/seat is being forced open psi will drop fast after a gradual rise in psi.
    As far as the tank venting u should have a least 1 vent line from the tank to the engine comp to the evap can if its still there. If no can then the line could be plugged off.
    If the problem just started probably not that tho.
    Some also have a return line off the pump back to the tank. 3 lines on the pump has return, 2 lines no return.
    As far as the cap goes leave it loose to test.
     
  12. blazer74

    blazer74 Member Premium Member

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    Oh and if it starts normally after it cools down it still has fuel in the carb even tho it's showing bubbles in the filter, so it should start warm.
     
  13. bent72

    bent72 Desert Solitaire Premium Member GMOTM Winner

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    No, straight back to the tank
    that's just the filler vent. Tank also has a vent in the sender

    My line split on the top, out of sight. No leaks. But identical conditions as yours.
    Worth a quick check of the line from the tank to the pump
     
  14. zackmoxley

    zackmoxley Registered Member Premium Member

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    The filter empties out. Not just showing bubbles. As far as the charcoal can goes, the only thing connected to it is the vent tube to the gas tank. Should i unhook it and let it vent to the air?
     
  15. bent72

    bent72 Desert Solitaire Premium Member GMOTM Winner

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    That should have no effect on the fuel line
     
  16. zackmoxley

    zackmoxley Registered Member Premium Member

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    This will require dropping the tank?
     
  17. bent72

    bent72 Desert Solitaire Premium Member GMOTM Winner

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    Should be able to check most of it without
    Since the pump was just out, start there. Any place the rubber line turns would also be a likely spot for a hole

    Mine was a 1/4" long split. Saw it with a little round inspection mirror
     
  18. blazer74

    blazer74 Member Premium Member

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    The vent to the can allows vapors from the tank to collect in the can after shutdown( keeps the garage from smelling like fuel or escaping to the atmosphere hense the first emissions).

    When starting the vehicle these vapors are drawn into the carb and burned in the engine assuming it's all hooked up correctly.

    The gas cap vent which allows air to be drawn into the tank if it was to become clogged the vent line to the evap can would serve the same purpose to prevent a negative pressure in the tank which can cause fuel delivery issues.

    Even tho your fuel line is draining which your fuel pump should prevent to a certain amount because it is self regulated to whatever psi it delivers your carb should still hold fuel in the bowl for restart from 10 minutes to several days depending on evaporation rate.

    I run a edelbrock street pump that (6psi) allows drain back after a short time with no starting problems other than after sitting a few days and the fuel in the carb evaporates, and even then doesn't take much.

    The only time I had starting problems like your having is when my old stock design fuel pump was putting out to much psi and held pressure after shut down and caused fuel press to rise from heat expansion up to around 10 psi on my online gauge causing flooding by overcoming the needle/seat in the carb and hard starting warm.

    Replace all your exposed rubber fuel lines from the tank to the carb and can with a quality fuel line for ethanol fuels first like bent72 has encountered cracked hose.

    I use fuel injection hose.
    Hopefully that will cure the problem, but if not you have other options.

    Also today's crappy aftermarket fuel pumps sometimes put out to much pressure for carbs causing troubles only exasperated by ethanol fuels.
     
  19. bent72

    bent72 Desert Solitaire Premium Member GMOTM Winner

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    I'm well aware what it does
     
  20. blazer74

    blazer74 Member Premium Member

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    That wasn't really for u specifically but either way a cap with a plugged vent hole and a tank vent line that is plugged off or not connected correctly can effect fuel delivery via the fuel line.
     

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