[1QuickS]

Item #12 is an air bleed jet that helps emulsify the fuel drawn into the mixing "barnacle" screwed to the side of the carb body. The only time fuel is delivered through this "barnacle" is when the engine RPM is high enough and the solenoid is activated which allows fuel to be drawn into the intake tract below the closed throttle plates...an emission era embellishment to reduce nitrous oxides generated by lean fuel mixtures.

Idling in your driveway will not activate this circuit. When idling the throttle plates will have approximately 0.0025" radial clearance with the throttle bores. The air that passes through this space has fuel drawn into it from the hole that the idle mixture screw meters; there is no fuel delivery from the "barnacle" contraption during idle operation. I recommend changing idle jets to something like 55s, perform the "Lean Best" mixture adjustment and be happy.

Suction applied at the port for the #11 metering screw must be great enough to overcome the "make-up" air drawn through #12 (air bleed) and the little fuel supply jet #4 must be clear of debris to supply fuel for this test; alternately you can take the top cover off the carb and blow into the hole with carb cleaner and look for bubbling from the #4 jet. Also, any fuel gallery blockage must be cleared.

Most recommend ignoring this system and blocking it off which is my recommendation as well; it was an attempt to bridge the time from carburated to CIS engines while complying with emission laws without resorting to the MFI cost burden to sale price.

If you are having issues with idle mixtures then your task is to follow the fuel delivery path from the float bowl to the idle mixture screws. All fuel (except accelerator circuit) passes through the main jet and enters the bottom of the emulsion tube well. From there it has two paths: one is up the well and out the hollow wing of the auxiliary venturi which is the path for the "main" circuit; the second path is from near the bottom of the emulsion tube well, up a fuel gallery where a horizontal gallery intersects it (this is where the idle jet is installed) and then back down the external gallery that feeds the progression holes (behind the big, brass screw/plug) and finally to the mixture screw at the bottom. This inner, vertical passage way is difficult to isolate and blow out due to so many different fuel paths near where the main jet resides.