first check the adjustment of the throttle cable. if its too tight it will do this. make sire the pedal is not stuck on the carpet of anything. check to make sure the throttle arm on the carb is returning to its "idle" position the entire way. if the cabe is not the problem look for vacuum leaks around the base of the carb, at the intake manifolds and from the dizzy.
if you find nothing wrong with the cable or with the vacuum than you need to adjust the carb. on the left side as you look at the carb there will be 2 screws. the larger one is the idle/air control screw. turn in clockwise to lower the idle (dont hold me to the clockwise).