How do I get Idle speed down other than idle adjust screw?

Discussion in 'Motorized Bicycle General Discussion' started by Airbuzz, May 27, 2009.

  1. Airbuzz

    Airbuzz New Member

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    Hello Forum members.

    My latest build has a 47cc Roundhead purchase from Zone 8. A couple of days ago I fired it up for first flight. She started immediately, and runs just fine. I'm still going easy on the throttle for the break-in period. One thing however is the idle speed. It's too high. I can back the idle adjustment screw all the way out and it still idles too high.

    What other adjusments can I make to slow down the Idle speed?

    Thanks. I appreciate your help.
     
  2. Denver Dave

    Denver Dave New Member

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    Take your air filter assembly off and see where the valve is sitting. It should be able to close completely with the idle adjust screw out.

    It is possible your throttle cable is binding somewhere or you have the adjustment barrels turned out too far where it goes into the throttle grip and/or the carb. Make sure those are turned all the way in.

    Does the throttle grip move smoothly with tension throughout its whole range?
     
  3. Cabinfever1977

    Cabinfever1977 New Member

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    when you twist the throttle for acceleration,you sometimes have to twist it back the other way or it will stick and stay high idling.your cable might be kinking up somewhere,they dont like to be tied in tight bends.

    stock throttles dont always snap back and will stay at a high idle unless you twist it back the other way.
     
  4. Airbuzz

    Airbuzz New Member

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    Denver Dave,

    When you say the adjustment barrels, do you mean there is some adjustment to be gained from the screw cap where the cable enters the top of the carb ? Where is the second adjustment barrel ?

    As to kinks in the line...everything has generous radii.

    More suggestions would be very much appreciated.

    Thanks
     
  5. 2door

    2door Moderator
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    Dave is refering to the adjustments at each of the end cable. At the twist grip and the carb. Start with them screwed all the way in and adjust from there. There is a trick to setting the idle screw too. You'll have better luck if you open the throttle, twist it to the accelerate position then screw the idle screw inward. The idle screw has a tapered nub on the end that engages a slot in the throttle barrel. When you screw it in it keeps the throttle open slightly and screwed out it allows it to close more. If you've had the throttle slide out of the carb make sure you reinstalled it correctly. There is a long slot in one side and a short one on the other. Align the long slot with the protrusion in the carb so it slides up and down easily and the short slot to the idle screw side. Installed 90degrees out it can bind making for a firm throttle and unsatisfactory idle adjustment. Hope this helps.
    Tom
     
  6. Creative Engineering

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    Airbuzz,

    Cabin may be right on this one!...I had the same thing happen on two installs.

    The throttle handle and casing were poorly matched. This caused the throttle to hang just off idle...i.e. the throttle wouldn't return all the way unless you twisted it backwards.

    Jim
     
  7. zendiecut

    zendiecut New Member

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    One thing I found when I took the whole throttle/carb apart was that the ends of cable were solid without adjustment. When looking into the intake end of the carb, I could see the "Barrel" was set too high. The only way to lower the barrel was to trim about 1/16" off the throttle stop inside the twist grip. As soon as I put the whole thing back together, I could adjust the idle with the set screw. The bottom line, the cable length was too short!
     

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