Won't run with gas cap on...

Discussion in '2-Stroke Engines' started by anachronism, Apr 4, 2008.

  1. anachronism

    anachronism New Member

    Anybody have this problem? I built one of what I am assuming are known as the "happy time" kits.

    It has been running great, except for one issue- With the gas cap on, the engine will stutter after a few minutes. Opening the gas cap resolves the issue. It seems that the gas cap is making an airtight seal, creating a pocket of suction at the top of the tank that keeps gas from flowing down the line.

    Any suggestions to resolve this?

  2. HoughMade

    HoughMade Guest

    You have correctly identified the problem. It needs a vent of some sort. A 1/8" hole in the middle of the cap works, but some fuel may splash out.
  3. BSA

    BSA Guest

    Hello anachronism and welcome to the forum. Please introduce yourself in the correct section so that we can all say Hi.;)
  4. I have never heard of a stock happy time gas cap doing that. That must be a really good seal. It's supposed to vent. On your cap do the thongs that hold the cap in place give way to the springs inside?
  5. sparky

    sparky Active Member

    Is it possible to pressurize the fuel system on a happy time? If you got a new carb or something, would it be fairly cheap & easy?
  6. fastboy9

    fastboy9 Member

    Ye this was happening to me as well, I just drilled a small hole in the top of the cap as a 'breather', most dirt bikes have these. That will sort out the vacuum problem out straight away