I have had some stumbling issues with my 292 on occasion, and in general it is not as responsive to throttle input as other carbureted engines I have fiddled with.  When I rev it by hand in park, it is like the engine sucks air for a moment and then catches up speed.  It isn't terribly slow to respond, but I know it isn't where it ought to be.

I have noticed that when I operate the throttle, the overtravel lever does not quite keep up with the throttle shaft's motion.  On other carbs I've examined (a Motorcraft 2150, today) the overtravel lever matches the throttle exactly until it reaches its stop, at which point it stays put as the throttle continues to rotate towards WOT.  If I help the overtravel lever with my finger, the pump squirts more aggressively down the barrels.  I believe this to be the primary source of my acceleration issues.

What I'm wondering is the specific source of this issue.  At first I thought there was a clog in the accelerator pump circuit, increasing the resistance to the fuel flow and thus the motion of the overtravel lever--but now I'm more inclined to think that the spring between throttle and overtravel has merely lost its oomph over 50 years. 

Has anyone ever encountered this issue?  If the spring needs replacing, where would I procure one?

EDIT:  Forgot to specify that the carb is an original '59 Autolite 2100.  I also have a Motorcraft 2150 I could rebuild and use...  it has 1.08 venturis as opposed to the autolite's 1.02 and it also has variable high speed air bleeds.  Perhaps a better option than trying to source a spring?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive