For what it's worth, here's basically how this carb works.
There are two brass tubes inside the intake horn. Air enters both.
One tube, on the choke-lever side (right side of the bike) is idle air supply. There is a tiny fixed idle-fuel jet in this pathway below a protective cover screw. Incoming air causes a venturi effect and draws idle-fuel up from the emulsion chamber and through that idle-jet.
This fuel mixes with the air entering the air tube. This too-rich mixture then goes forward past the idle air/fuel mix adjustment screw where the rich idle mixture can be metered and leaned out with more air. The adjusted mix is then finally sprayed into the butterfly-throttle area.
Running fuel supply:
The larger, longer brass inlet tube (left side of bike) is the one that provides emulsion air for normal running. This tube's air goes directly into the top of the emulsion cavity.
Fuel rises through the main jet and into the perforated brass emulsion tube. Air is allowed in through the perforations.
This premixed bubbly fuel/air mix is then sucked up into carb's venturi and into the engine.
On this style of carb (butterfly) it is vital that the larger fuel droplets be broken down into a mist. The emuslion tube does this. If enough emulsion air is not supplied the carb will deliver a very poor mixture that wont burn well... Drops of fuel will likely foul the spark plug.
So, not only is fuel mixed with the air coming into the carb's large throat, fuel and air must also be premixed inside the emuslion tube cavity..