Rebuilt kt100 idling extremely high

Hi Guys. I just had my kt motor with 4 hole can rebuilt. When I start it on the stand, it revs really high. Maybe 6k rpms…high needle is at 1/4 out & the low is at 1-1/2 turns out. The idle screw on the carb is barely touching the lever…I have to be missing something simple…Also, there is no kill switch. Is covering the intake the best way to shut off the motor? john

If I remember right that would happen sometimes with me. I would “feather “ my hand over the intake as the rpms start to clime to get it to settle down then open up the low side(tall needle) to ritchen it up and bring the rpms down. If the carb is built for racing it won’t idle. Hitting the gas peddle is the only way to keep it “idling.” No kill switch.

Did you send the carb with the engine to your builder that time?

Check the carb and mounting for gasket condition and leaks. I can’t soeak specifically about idle on the KT, it I have heard that the “best” setup usually involves them not idling on the stand.

That said, it sounds like your engine might be “racing a little which makes me suspect an air leak.

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That carb setting seems really low. When I was running Yamaha a couple years ago we ran like 2.5 on the low and 1/8 on the high end at most.

James is right though, for a Yamaha to run best it wont be able to idle at all without an idle screw, which I never had on the engine and really shouldn’t be needed on those motors with a high stall clutch.

Yes, carb was rebuilt as well. Tried it again with different car settings & motor immediately revs up to 5000 rpms and stays there. Going to contact the builder.

Going to your builder is the best thing you can do. You may have an air. Make sure the builder does a pressure check.
Is the throttle plate closing all the way? If your builder broke the engine in for you, he may have cranked the idle up.

I turned the low needle out 2.5 turns & it starts and runs normal. Thanks for every ones help.