They were originally used to balance air flow and idle speed on non electronic idle motor systems. (The engines with the auxiliary air valve where the electing idle speed control valve should be).
I personally use this to an advantage to get rid of the idle and off idle hunting. I described this in Post No.19 in:
http://dmctalk.org/showthread.php?15...umpiness/page2
As far as the air admittance deceleration springs, you could either replace the throttle assembly in its entirety, replace the throttle plate discs, or solder then shut.
Good luck
NickT