there's only a couple reasons it would be stuck. throttle control, bad cable, slide in the carb is stuck. the first thing you need to do is determine what is free and moving and what isnt. i would start at the top since thats the easiest part. does the throttle move at all? if something is stuck further down, it should roll back and forth. right underneath the front brake lever there is a little tiny slot head screw that sits in a slot milled into the brake lever assembly. this is the clamp where the throttle wire is connected. does it move when you turn the throttle? it should slide left to right in the slot. if the cable is froze up, the sheave will be pushed out of the throttle assembly as you turn the throttle to its idle position. if thats the case, you need a new throttle cable. if the throttle wire inside the sheave moves freely, then you need to move down to the carb. this is the hard part only because you must drop the engine to get the carb off. it can be worked on by taking out the two top engine mount bolts, and loosening up the rear wheel and releasing the chain tension. there are two screws in the very top of the carb that hold the black plastic cover on. removing this cover gives you access to all the throttle slide assembly in the carb. i recommend a moped mechanic for this part.