Another very informative post by Yeti on YB.
“At part-throttle and the low airflow conditions present near the beginning of and in the lower range of main discharge flow, the addition of emulsion air causes richer fuel delivery with the same size jet and venturi vacuum signal because the addition of air to the fuel in the main well pushes the fuel up the well toward the discharge nozzle in the booster (the same as carbonation foam pushes beer up and out a longneck beer bottle). In carbs with the main system flow path dimensions similar to the common Holley 4150, adding emulsion air causes low flow to be richer before it causes high flow to be leaner.”