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carby idle screw problems

Discussion in 'Technical and Troubleshooting Torque' started by Gordo78, Sep 25, 2006.

  1. Hi everyone. It's my 1st post so go easy on me.

    I've been trying to get my 1990 DT175 running after it sat in the shed for 4 years while I was overseas. I've cleaned it all up, change fluids/plugs etc, but I've got a problem with the idle.

    I was having trouble starting it after cleaning the carby. first it wouldn't start, no it does after fiddlig with the idle screw but revs at max and won't idle normally. I've tried the screw all the way in, out, halfway etc. After that I took the idle screw out I noticed the O ring had broken. I bought a couple o rings from a local supplier (there's not many bike shops up here), ones to thick, ones a tiny bit to big in diameter, both have the same problem, revs to it's max and won't idle.

    I'm not much of a mechanic but want to use this bike to learn how top fix bikes before I upgrade. Can anyone shed some light on why my bike is revving so hard? Will the right size O ring fix my problem or have I done something to the carby when I put it back together. Any help will be really appreciated.

  2. OK a few idiot questions just in case.

    Does your throttle have a bit of free-play?

    It's not hard to ge the situation where the cable sits up in a socket and thus opens your throttle.

    You are aware there is an idle adjust and a mixture screw?

    Playing with your mixture won't have much influence on the revs much just dirty things up.

    Also, I think that's a 2-stroke. They rev harder when there is no oil in the fuel. Make sure that side of things is good too.
  3. I checked the throttle and it has play in it. Yes, I'm aware of the 2 screws and it's definately the idle screw I'm talking about. Yep, 2 stroke, but will check the oil feed but it shouldn't make it rev as hard as it is, I'm talking FULL REVS!

    When I put the throttle valve and cap back on I had to play around to get it right, Is it possible the orientation of the throttle valve is wrong? Would it even run if it was wrong?

    Thanks in advance
  4. I'm not positive about the DT but I know some carbies can accept the plunger 180 degrees out but will stick half way up even though the top screws on. Does it feel like the throttle moves right? Checked in the back of the carby to see if it moves up n down?
    I don't think a bike can get full rpm if the throttle body is closed so it seems like it's stuck open, not so likely the idle or mixture screw.
    Hope this helps.