Got my C4 a few years ago, second always shifted to soon, the engine would lug and ping. Searched the entire length of the throttle cable for the D adjustment and found nothing! Then one day I had the air cleaner off and noticed on the throttle linkage change over hinge bracket a tiny cable through a hole in the bracket. When the throttle moved it pulled the cable! A light bulb came on in my head. I pulled the cable and crimped a little wire over it to make it shorter. It worked !!! Sorry, I didn't take a picture. Apparently some of the early 84's had this. I'm sure that the previous owners had tried to have it fixed. Hope this will help someone.