Extra Venting Outside Air Horn at Idle

Pre-Complex pollution control-Rochester added a float bowl vent outside of the air horn so less float bowl vapors would vent into the idle air stream.  (The sprung rubber flapper would be opened by a link to the accellerator pump)  In the Idle position the link on the accerator pump lever would lift the boal vent.  This would mean that during off idle and cruise conditions the flap would be closed and burn vapor through the engine, but during idle vapor would exit past the open valve.

While this valve will open at any temperature. It helped to provide smoother idle because idle mixtures would be more consistant especially when float bowl fuel vaporized more at warmer temperatures.