The throttle cable you can get at by pulling up the floor rubber and the panel there. Check that, it goes to the top of the transmission on the governor arm. The other side of the arm is connected to the throttle on the carb. Make sure nobody stuck something in the linkage to keep it open. Some take the cable off and hook it direct to the carb, you can also drill out the shaft hole in the arm to disable the governor and make it go fast. Make sure the carb is not rotating in the rubber boot, if so remove and clean with carb/brake clean and put back in. The valve in the exhaust should be fixed open, that is ok, all it really did was make it slightly quieter at part throttle and its really not needed some don't have it.
This is the governor arm, you can put vicegrips on it like this to temporarily disable the governor but eventually it will break the throttle cable from excessive pressure. Make sure it does not bind on the intake hose, use the small pocket vicegrips. The rubber bellows there on the arm is the cable from the pedal. The long part of the arm runs the carb.
The other end of the arm and carb photo here:
http://www.buggiesgonewild.com/gas-y...5670-carb.html