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How do you fix vapor lock

Discussion in 'Mechanic and Repair' started by TRX250R, Jun 7, 2008.

  1. TRX250R

    TRX250R LawnSite Member
    from RI
    Posts: 24

    I have a craftsman w/ a 15.5 horse Kohlor and half way through the lawn it dies. I look at the fuel filter and its empty. I tried removing the fuel cap, but the fuel won't fill. If I come back a hour later the mower starts up again. Thanks for any help -Walter
  2. Firefighter337

    Firefighter337 LawnSite Senior Member
    Posts: 373

    Dealer worked on a friends weedeater with a vapor lock issue. There were 2 lines running from the carb to the fuel tank. A supply and return I'd imagine.

    From what I saw, It appeared that on one of the lines he put a "T" on it and with another very short peice of fuel line, he put a check valve. Allows air in, but does not allow fuel out.

    I do not think this has been done before. Kind of a "rigged" way to get the job done. But it works great.

    The problem I see with this, When you have unfiltered air going to your fuel tank, you will have debris enter the fuel tank causing more problems.

    I was thinking a vent or something to screw into the top of the tank. Making it work without leaking might be the tricky part.
  3. jkason

    jkason LawnSite Senior Member
    Posts: 548

    Most "vapor-lock" issues are with the temperature of the air going past the fuel line.

    Get some of that pipe insulation at HD or Lowes that is the diameter of your fuel line and put it over the line anywhere it's exposed (not near the muffler, obviously).

    Should take care of the problem.
  4. 44DCNF

    44DCNF LawnSite Bronze Member
    Posts: 1,460

    An older SRM 2100 I had used a system like this with a tank vent, on a seperate line I t hink. I think the one way valve used was a filter itself. You also still have the fuel filter in the tank to filter any debris that came in through a vent.
  5. Varsity L&G

    Varsity L&G LawnSite Senior Member
    Posts: 418

    Wooden Cloths pins always worked on VW's
  6. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    I would start by checking the inside of the tank for debris(leaves,grass,plastic,etc.) and make sure that something is'nt getting sucked down onto the fuel outlet and then floating off after you stop and let it sit.
  7. 44DCNF

    44DCNF LawnSite Bronze Member
    Posts: 1,460

    The needle and seat may be sticking. It would seem if a vacuum was forming in the tank, it could draw the tip of the needle into the seat hard enough to cause it to stick. If it is deteriorated it could stick. It may need replacing but....

    You say after it dies, you open the gas cap but don't see fuel flow. Did you do it right away? Did you hear, or not hear a the tank release vacuum? If this happens again open the cap and then rap on the side of the carb lightly with the handle of a scredriver near the fuel inlet. That may cause the needle to fall free if it is in fact hanging.
  8. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 921

    Don't even worry about how full the filter "looks", until you have checked for spark immediately after it quits.
    Many fuel filters "look" empty, but the engine keeps running.
  9. bojodunk

    bojodunk LawnSite Member
    Posts: 37

    you did not say if this is a new problem or not
    try keeping the gas cap a little loose next time
    (try the easy things first) it sounds more like
    the tank is air locking

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