Welcome to the board. I have a suggestion. When you post a question, make sure you let people know that you have an 85 with a sc engine or put that information in your profile. Check the return spring for the accelerator cable inside the engine bay. Move the mechanism by hand and feel if there is any resistence. You can give the linkage a shot of WD-40 or other lubricant to loosen things up. A strand of the cable or plastic sheathing could have broken at the end, causing the cable to hang up when sliding through the cable sheathing. The previous owner may have re-routed the cable when he converted the engine and the cable may be excessively bent or slightly crimped. Also, look under the dash where the throttle cable enters the cabin an check to see that nothing is interfering with the movement of the accelerator pedal and cable.