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125sx ideling to fast

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The screw on the carb that has the spring on it only changes the idle speed a little. My bike is idling way to fast after I changed the spark plug and dropped the main jet size. I can screw it all the way in and the bike still idles fast. Is that the air/fuel screw? What is the other screw that you use to adjust idling speed. Which one is more important?

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The idle speed screw is the black plastic one and you can adjust it with your fingers (just). The air screw is the one you need a small slotted screwdriver for. You set the bike to a fastish idle using the idle speed screw, and then adjust the air screw to get the idle nice and smooth. Once the idle is smooth, you readjust the idle speed screw to what you want. Both screws are important.

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Air screw start off 1.5 turns open, but could be anywhere from 0.5 to 2.5 turns when you adjust it. If you need more than 2.5 turns for good steady idle then you need a leaner pilot jet, it you need less than 0.5 turns open then you need a richer pilot jet.

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where could the air leak be at? How tight are you supposed to screw down the screw that attaches the carb at both ends. one end leads to the air filter and the other leads to the cylinder. I tightened them extremely tight.

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If there was an air leak created from removing or rotating the carb, it would be on the hose between the carb and the intake manifold. Any air entering the intake track AFTER the carb is what will cause a hign idle.

The hose from the air filter to the carb is irrelevant to your problem.

The clamps SHOULD NOT be cranked tight! They need to be snug but over tightening will damage the rubber, may create an air leak, and on some of the vintage carbs..... this can actually warp the slide!

When I take the carb off, I lightly coat the rubber inside edge with grease. This helps to slide the carb in, as well as creating an air tight fit once the clamp is snugged up.

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