I'd get a maintenance manual from http://www.haynes.com and understand how the "throttle" works when you move the throttle control handle. Maybe the throttle cable is sticking and needs some WD-40 spray lubricant applied. Spray it everywhere the throttle cable runs all the way to the carburetor linkage. Make sure you can see things move when you exercise the throttle control grip.
Sounds like your throttle is stuck open, either it is stuck or your cable is broken or the throttle body return spring is broken and is not making the butterfly return to it's position.