vapor lock
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vapor lock

  1. #1
    tintingsandiego krusn56's Avatar
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    Default vapor lock

    Has anyone here had this problem....I had a fuel line ran between my front motor mount and oil pan for a clean install. Runs at 5 1/2-6 1/2 lbs with a carter mech pump cold. Once I have taken it out it has read as low as 3 lbs warmed up. I have replaced gauge, 2 pumps, lines, fittings, drained the tank with a flush and new filter on both water sep and gas. I am in the process of running a more direct shot to pump. Is this possable for a fuel line being close to my oil pan to cause this?
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    Senior Member GT Jets's Avatar
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    Quote Originally Posted by krusn56 View Post
    Has anyone here had this problem....I had a fuel line ran between my front motor mount and oil pan for a clean install. Runs at 5 1/2-6 1/2 lbs with a carter mech pump cold. Once I have taken it out it has read as low as 3 lbs warmed up. I have replaced gauge, 2 pumps, lines, fittings, drained the tank with a flush and new filter on both water sep and gas. I am in the process of running a more direct shot to pump. Is this possable for a fuel line being close to my oil pan to cause this?

    IMHO Yes....I would also suspect an improper tank vent, pulling the tank(s) into a negative....

    A quick experiment would be to put some water in the bilge and see if the problem magically vanishes...
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    tintingsandiego krusn56's Avatar
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    I have a belly tank with a rex marine vented cap...both tank and cap are new.
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  6. #4
    Cas
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    with a belly tank, I doubt the fuel is able to get hot enough for it to vaporize. It will be moving through the hose fast enough for it to stay cool enough to remain a liquid.
    Not only that, if the fuel vaporizes, the engine will be way down in power and would more than likely die. It would also be very hard to start until the carb got some liquid fuel into it.
    I had an older Chevy van that would vapor lock in hot weather due to the metal fuel line being so close to the engine. All I did one time was to clip 5 or 6 clothes pins to the line and never had the problem again.
    Last edited by Cas; 08-23-2010 at 09:04 PM.

  7. #5
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    K 56,

    You can check for venting by loosening the cap and checking the pressure. I don't know where your tanks are but be sure that you keep the water out.
    I have side tanks and they have a 1/2 inch diameter hose with about 1ft of loop in them for venting.
    I thought I had a venting problem but mine turned out to be an air leak on the input to the fuel pump.

    Good luck

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    tintingsandiego krusn56's Avatar
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    I run my boat at 35-38...and as high as 4200. My plugs are reading lean after a run...Once I am home and run it cold, everything seems fine with the plugs reading normal.
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    Cas
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    you could always get a length of 5/8" heater hose, cut it lengthwise and slip it over the fuel line. If the problem goes away, you will know something is going on there. If nothing changes, you will need to look elsewhere.

  10. #8
    tintingsandiego krusn56's Avatar
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    Quote Originally Posted by Cas View Post
    you could always get a length of 5/8" heater hose, cut it lengthwise and slip it over the fuel line. If the problem goes away, you will know something is going on there. If nothing changes, you will need to look elsewhere.
    Thanx... I already pulled the lines to replace and run them more direct. I had an olds in it before so everything was ran on pass side...thats why I had the line in front of oil pan. Going to run straight on dr side....
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