Carb sealing & Octane

Discussion in '2-Stroke Engines' started by JTinFL, Jan 9, 2010.

  1. JTinFL

    JTinFL Member

    What are symptoms of the carb not being sealed when attached to intake manifold?I'm running a Grubee 66/80 and I think it runs ok,but being new at motorbikes I probably wouldn't know the differance.Differant subject,should I use low octane gas or higher octane?

  2. give me vtec

    give me vtec Active Member

    89 octane... dont need anything higher.

    Intake can leak in two places... basically on both ends. I would get a set of Allen screws and a carb o-ring from sick bikes. Use the allen screws in place of the stock studs... the carb o-ring goes in between the carb and intake tube. Tighten everything down very good.
  3. give me vtec

    give me vtec Active Member

    symptoms of a leak are; four stroking at high rpm's, odd idle characteristics, and an excessively lean combustion evidenced by a white tipped spark plug instead of a nice tan. After long exposure, the excessively lean conditions can wreak havoc on your engine.

    I would just make the improvements i recommended so you don't have to even worry about it. If you need help getting the stock studs out send me a pm and I will help you.
    Last edited: Jan 9, 2010
  4. AussieSteve

    AussieSteve Active Member

    No, a lean mix will not cause 4-stroking. That's a sign of a rich air/fuel mixture. The rest is right. Don't confuse the poor guy.

    Further to this, an 'O' ring butted up against the end of the inlet tube will not necessarily ensure a good seal, although it certainly helps.
    First ensure that the inlet/cylinder gasket is sealing properly, with or without allen-head screws.
    Then spend 30 minutes doing this.
    Now you can tune the carb with confidence. Each time you put it together it will be the same.

    ... Steve
    Last edited: Jan 9, 2010
  5. give me vtec

    give me vtec Active Member

    I saw that... its my next project. Very good job/idea.
  6. AussieSteve

    AussieSteve Active Member

    I was apprehensive when I started, but it's surprisingly easy to file a good groove. The nearer to the end of the tube, the better.

    ... Steve
  7. JTinFL

    JTinFL Member

    Four Stroking

    At the chance of sounding ignorant,what's four stroking.Bear with me guys.
  8. AussieSteve

    AussieSteve Active Member

    A 2-stroke engine '4-strokes' when the fuel/air mix is way too rich. The engine tends to fire every second revolution instead of every time.

    See this thread. There's a link to a YouTube video that illustrates 4-stroking very well:-

    NT Carb Tuning Basics

    ... Steve
  9. EnFlaMEd

    EnFlaMEd Member


    This is how I have mine sealed up.