Ford called that same system an "economizer" and it consisted of a screw-in device about the size of a quarter with a rubber diaphragm and a cone shaped valve in it. A spring held the valve in the open position and engine vacuum would overcome the spring and hold the cone plug closed. Anytime vacuum dropped below a preset point, the valve would open and bypass the main jet(s) to provide a rich mixture. Ford (and Holley) made several valves with different spring tension and different orfice sizes to control when and how much enrichment was available with the valve open. That feature made those carbs more tunable that Rochesters, where the power system was more of an on/off situation.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!