I don't run a 4100. (I have an Edelbrock.) But I did return my car to the factory setup for the throttle and return spring. Somewhere along the way, this gets taken apart and put back together with some of the pieces missing. I have a 64, so I was missing part 9B853, shown in this diagram:
I believe for all flairs, the main throttle return spring runs vertically from the top of the linkage down to a connection on the top of the bellhousing, in your case part 7C431 I guess. Here's how mine looks:
~Steve