KR-1S.co.uk Forum

Hi all. Have just restored an AR125B for my stepson and its revs uncontrollably despite the throttle being shut. It ran ok for a day and has developed the problem.
I have cleaned out the carb and this seems ok. Fiddling with the idle screw does varoius things ie if too low it ticks over and then dies or if you turn it up a bit, it revs to 10-11k and stays there. If you then hit the kill switch and let it drop to say 4k and hit the kill switch again it stays at 4k until you twist the throttle again, and then it revs uncontrollably again.
Its many years since I had a 2 stoke. What may be the causes if anyone can help?
The bike had been standing for many years before we got it. We had a top-end rebuild at a bike shop and the main bearings were ok.

Thanks for any help in advance.

Sounds like an air leak. Or the carb slide is sticking.

Agree with Strokerboy.

Assuming the carb has been cleaned and jetting/needles are standard...

Take off the airbox and check the operation of the slide. You should be able to see this if you look down the carb inlet when someone else opens and closes the throttle. I've had this problem before when the resin 'nib' that acts as the slide guide in the VM vertical slide shaft had perished.

Also check the rubber ring that holds the carb to the disk valve cover to ensure it's sealing properly. Check you don't have a leak between the disk valve cover and crank case.

Check the needle is seated properly and the clip is set in the middle.

Check the pilot jet is thoroughly clean and seated properly - I have had a problem with unpredictable over revving when the standard pilot was blocked. I have also had the same problem on a tuned AR when the standard pilot jet was too small.

Obviously.. Check throttle cable not sticking etc

And if all that fails (and you want the bike to look standard) stick on another carb, preferably one with a separate pilot screw such as a VM26 (off a KMX)

Hope that helps