For anyone viewing this looking for info -
Yes, that's the ground speed governor. The accelerator pedal RELEASES the throttle which is spring loaded open. When the driven clutch spreads it contacts the end of the arm which pulls the cable and draws the throttle back toward idle speed. Setting it is simple - loosen the cable stop so the end of the cable at the governor arm is free. The end at the carb should have an end cap on it and the cable will be going through one of the holes on the throttle arm. Open the throttle fully and pull the cable snug. Set the governor arm so it is just touching the button at the center of the cap on the driven clutch. Secure the cable at the governor arm. During test drive, hold the accelerator pedal all the way down. The cart should go right up to max speed then the engine will slow down and the cart will continue at the same speed. Encountering a hill will cause the engine to speed up as soon as the cart starts slowing down.
I had to add a return spring to my governor arm to keep it from sticking in the "governed" position. Maybe there was one there originally, I don't know. but I have one there now. You can get a little extra speed by slacking the cable a bit, but too much slack on mine seemed to completely disable the governor function so I left it close to standard speed.