Thanks for the response guys. The issue is either in the cable itself or the linkage as suggest. On Pontiac Tri-powers I am running on the center carb only until I kick it down to open the front and back two. So, it's either in the center carb which will be proved out by doing exactly what Itoldyouso suggested or it's a bent throttle shaft as Dave said. I'll check that over the weekend and see if I can isolate and fix the problem. Thanks again for your help!
Steven