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high reving when cold

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my 05 yz 125 revs about half throttle now for some reason. It also seems to get worse the colder it is out. Yesterday it was about 32 out and reving to the moon and i had to keep hitting the kill switch for a sec to try and get it down... it was especially worse in neutral. any ideas of what it would be? my bike was very rich in the summer so i thought the jetting for the winter would be OK. thanks

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i turned in the airscrew and it helped a lot but i will bump up a size on the pilot. but it is still revving high when first started. I checked for air leaks and havnt found any

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My 02 Yz125 did the same thing because there was an air leak around the intake boot.

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I use a thin bead of silcone to help seal the boot to the reed block.

Still sounds like you may be lean on the pilot to me... IDK what normal temps are when you ride durring summer months but 32 is quite cold and def. calls for richening up the jetting all around. Id be weary of the main as well. A tell tale sign is if you have a hanging idle when you pull the clutch while there is a load on the motor.

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you are running lean, and when it´s cold is worst, because cold condition lean your mix, may be you have burn crank seal left side.

Or you have dirt on your carb.

try to fix it because you can destroy top end.

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Winter weather requires richer jetting in most areas.

Another possiblilty that hasn't been mentioned is the throttle cable being hung up. Check where the cable goes into the throttle housing and also where in enters the carburetor.

If you don't have a little bit of free-play in the cable when the throttle is closed, it could be holding the slide open ever so slightly.

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The bikes idle does race when i pull the clutch in while the motor is under load, and when i stop and have the clutch pulled in.. but only sometimes. I pulled the plug and it looks like its running rich, but could it be running lean in the pilot still but the plug is showing the jetting for the needle and main?

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The bikes idle does race when i pull the clutch in while the motor is under load, and when i stop and have the clutch pulled in.. but only sometimes. I pulled the plug and it looks like its running rich, but could it be running lean in the pilot still but the plug is showing the jetting for the needle and main?

Correct... I had the exact same issue with my 250 after the rebuild when I got it. Plug showed it was rich but the it was lean on the pilot. Ended up going up 2 sizes and no more lean surge.

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