[Kenth]

Dick, the added air channels is a part of the adjustable off-idle air bleed system.
An adjustment screw is located at the end of the channel to control the amount of air bleeding into the system.
The off-idle screw is adjusted at the factory to maintain very accurate off-idle air/fuel mixture ratios.
It is adjusted during carburetor flow test, then capped, and no attempt should be made to readjust in the field.

The single brass tube is a part of the fuel POE system adding fuel at hard acceleration and high speed driving to compensate the somewhat lean main jetting for economy. At approximately 8 pounds of air flow per minute and above, the fuel begins to feed from two discharge holes located in the air horn just above the choke valve.

HTH