Stuck throttle on 02 KTM 125 SX

John,
It may be that the throttle cable came through the spring in your carburater, this happened to me, its easy to test this, with the bike off feel if there is resistance on the throttle, does it retract at all? If not, loosen the nut on the cable (above the carb.) and then unscrew the top nut of the carburater, pull the slide out with spring, compress the spring (making note of the white plastic spacer with a tab on it, spring holder, align the tab on the white washer on the slide) then put the spring back on.
Hope this helps

I'm not sure if the cable came out in the carb, but maybe there's a couple other things:

1. The cable housing can come out of the throttle seat or the carb seat and make the throttle stick partially open. Make sure the cable housing is fully seated on each end.

2. Did you happen to raise the idle by misadjusting what your friend undid? There should be some freeplay before the throttle works. You can feel this by slowly turning your throttle. Nothing should happen for a couple millimeters, then you should feel the resistance of the throttle cable beginning to open the carb. If there's none, it's too tight and you need to readjust the cable.

Friends that mess up other people's bikes need to be re-evaluated for mental capacity! It's NOT FUNNY to mess with someone's bike adjustments if you don't know the consequences, or if you make it unsafe. Not cool. Tell your friend to grow up!

Kill your friend......

The cable may not be seated good around the pully in the mechanism.

My second guess would be the plastic retainer in the carb got screwed up a bit. If your cable is good to go on top, do what Speedway suggests and make sure your retainer is seated in the detent properly.