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  • Fuel System: vapor lock

    Can vapor lock occur any where in the fuel line, or is it just betweem the tank and the fuel pump ?

  • #2
    Anywhere that excess heat can get to the fuel...
    64 GT Hawk (K7)
    1970 Avanti (R3)

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    • #3
      The fuel can boil any place that it gets too hot, but some places are less troublesome than other places.

      The problem with vapor lock is when it occurs on the suction (inlet) side of the fuel pump. The fuel pump is designed to pump liquid, but cannot pump vapor or bubbles.

      Also the boiling point is determined by the basic nature of the fuel, the fuel temperature, plus the atmospheric pressure on the fuel. That's why it is more likely to boil on the suction side of the pump, because the pressure is lower.

      The fuel is less likely to boil on the outlet of the pump because it is under higher pressure. Even if it does boil on the outlet side, that is less of a problem as the pump is still sending fuel (liquid plus vapor) to the carb.

      You basically need to cool the pump and the inlet hose going to the pump. Or, you need to pressurize the inlet hose by installing an electric pump back by the tank.

      I always use the low pressure pumps marketed for foreign cars. They will keep fuel coming to the mechanical pump, but will not over power the carburetor inlet float.

      Also make sure that there are no pin holes in the fuel line. Holes can exist that are so small they will not leak liquid fuel, but when the mechanical pump is sucking on the line, air can leak in, causing bubbles in the fuel that the mechanical pump cannot pump.
      Last edited by RadioRoy; 07-17-2012, 11:16 AM.
      RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.


      10G-C1 - 51 Champion starlight coupe
      4H-K5 - 53 Commander starliner hardtop
      5H-D5 - 54 Commander Conestoga wagon

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      • #4
        I recently had vapor lock symptoms on my Avanti. In checking it out I found the neoprene line between the fuel pump and the steel line from the tank was so old that it was soft and easily could be collapsing. Car ran well after I replaced it. I understand the ethanol in today's fuels will attack the neoprene line and that a line meant for fuel injected cars will hold up much better.
        Doug

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