Thread: Idle curosity
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Old 05-22-2009, 09:11 PM
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Earthman Earthman is offline
Motorized Bicycle Senior Member
Join Date: Mar 2009
Location: Pittsburgh, PA
Posts: 82
Default Re: Idle curosity

With a warm engineÖ

1. Make sure your twist throttle is turning freely. Try twisting it further toward the off position and see if itís hanging up and holding open the throttle. If this doesnít workÖ

2. Make sure your throttle cable jacket ends are seated properly and the cable isnít adjusted too short at the top of the carb or at the twist throttle. If it is, it may be holding the throttle open. If this doesnít workÖ

3. Take off the top of the carburetor and take out the barrel (the cylindrical part that is attached to the end of the throttle cable and that goes up and down when you twist the throttle). If I remember right, there is a small slot on the side of the throttle barrel that has to line up with a small pin in the side of the carburetor to work properly. When I first assembled my carb, I misaligned the pin and the engine idle had symptoms like you describe. Once I reassembled the carb correctly, it worked fine.

[Iíve only built one motorized bicycle and have experienced all of the above.]

4. I donít think I had any air leaks to speak of, but I sealed the carburetor onto the intake manifold by putting a little gasket paste from a tube onto the flat round end of the manifold (see photo) before finally installing the carburetor Ė just in case. Thatís the only place I could see where there might be a leak.

As I understand it, the end of the idle set screw is tapered and the throttle barrel rests on it when in the idle position (assuming the cable isnít too short and moves freely). When you turn the idle set screw in, the throttle barrel rests on a wider part of the taper allowing the engine to run faster. If everything is working and installed properly, you should be able to set the idle low enough for the engine to quit and high enough to be annoying.

Unless the connecting parts between the carburetor and manifold are damaged, misaligned, or defective, I donít see many places where much of a leak could develop.

Good luck!
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Last edited by Earthman; 05-24-2009 at 08:44 AM.
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