I don't know of any bolt that goes through the throttle handle. Does it look like something original or something that somebody added?
If you have the throttle handle rolled all the way forward and the throttle barrel is not half way closed, you have to loosen the cable lock on the pulley and reposition the lever/pulley to a position where the barrel is half closed when the throttle handle is rolled all the way forward. When you roll the throttle handle back, the throttle barrel should open all the way. If you don't have the necessary travle in the throttle handle, I've got to think there is a problem with the handle somewhere.