Leaky gas cap?

Discussion in 'Motorized Bicycle General Discussion' started by Beej, Aug 3, 2010.

  1. Beej

    Beej New Member

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    Is there a quick fix for this? I tried the search and got nothing. I get a small leak from my gas cap whe I ride. Not too much but enough to drip down the tank.
     
  2. GearNut

    GearNut Active Member

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    Not to sound rude, but just don't fill your tank up so full.
    If I fill mine up all the way it leaks allover. I fill it to an inch or so below the top of the tank, about 2 inches below the filler bung.
    The only other guess that I have is that the gasket around your cap is not sealing well to the filler bung on the tank. Are their any gouges in the gasket or dents on the bung?
     
  3. nidyanazo

    nidyanazo New Member

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    The cap is vented.
     
  4. GearNut

    GearNut Active Member

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    You are correct, sir. If it were not vented, as the fuel flowed out of the tank, it would develop a vacuum and the fuel flow would stop.
     
  5. tim turbo

    tim turbo Member

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    I think the leaky gas cap is a common problem, so I took some inner tube and made another gasket. That took care of it!
     
  6. Beej

    Beej New Member

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    The tank is only half full at most. I will try making another seal.
     
  7. GearNut

    GearNut Active Member

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    Leather makes for a decent gas cap gasket material. Inner tube rubber will eventually swell up to almost twice it's original size.

    Edit: Sheet cork, available in hobby stores, also works very well.
     
  8. bairdco

    bairdco a guy who makes cool bikes

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    to solve the problem, take your cap off and set in on a hard concrete or metal surface.

    next, take a BFHammer and hit it as many times as you want. (note: cap must be hit as hard as possible.) (note 2: cap will try to retaliate by bouncing up and hitting you in the face. wear proper protection.)

    step three. dispose of cap properly.

    that will solve the problem of the leaky gas cap, but opens up another problem. "where do i find a new gas cap?"
     
  9. Beej

    Beej New Member

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    Baird, I smell what you're steppin in...
     
  10. kaizer_soze

    kaizer_soze New Member

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    I quick fix that worked well for me was to wrap the top of the lip of the opening in the tank with plumbers tape (not really tape, white, adheres to itself and fits to any shape). I had to cover the lip with at least 10 layers of the tape, but now the cap sits tightly and there is zero leakage even with a full tank.
     
  11. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    Inner tube rubber also dissolves in petroleum products. I have personally done this to prove a point. Leather and cork aren't too bad. But when I built my tank out of a softball bat, I realized I would need to make my own vented gas cap.

    I used a large, threaded brass fitting for my bung which had a companion threaded collar. I made a brass disk to close the end of the collar and turn it into a cap. I used a large ball bearing and a hammer to dish the disk a bit. I then drilled a hole for a rivet in the center and a vent hole just off-center, in the disk. I made a Nitril rubber washer to fit inside the disk.

    Nitril is ideal because it is NOT dissolved by gasoline. First I soldered the disk into place at the open end of the collar. Then I riveted the washer to the inside of my cap with a small brass washer in between. Air comes in through the vent hole and can get past the Nitril washer, but fumes can't blow out through there - the washer seals against the disk. It is designed, however, to vent from inside if you blow VERY,VERY hard. This is a stopgap against pressure buildup.
     
    #12 Allen_Wrench, Dec 9, 2011
    Last edited: Dec 9, 2011
  12. thegnu

    thegnu New Member

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    Heres a guy who does NOT fool around , Ima fan of the get a bigger hammer alignment system as well .
     
  13. Nashville Kat

    Nashville Kat Active Member

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    A thin piece of nylon material like the top of a sherbert or cottage cheese contaner is great and gasoline proof- you can put one or more UNDERNEATH the normal rubber gasket

    works every time!
     
  14. CroMagnum

    CroMagnum Member

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    Back in the 1970s I used to use a "Slopper Stopper" on my dirt bikes. Basically it was just a big foam rubber donut that stretched over the gas cap. It still let the tank vent, but when gas dribbled past the cap the foam would soak it up.

    Get some open cell foam and cut it in a circle a couple of inches bigger than your gas cap. Then cut a hole in the middle just about the size of the filler neck. Screw on your gas cap, stretch it over the cap and you're good to go!
     

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