Carter Thermoquads ~ 'More General Information'

the air bleeds above the venturi in the early CS series carbs, were "diminishing air bleeds", Qjets also used them on some models as well, they'll bleed air, but also discharge fuel at WOT high velocities to supplement primary main metering.

diminishing-well-bleeds.png

Diminishing Well Bleeds
Some solid fuel models use diminishing well bleeds. This bleed is subjected to venturi pressure changes that follow engine load conditions. They serve as self-adjusting air bleeds and at or near the wide-open throttle, could deliver fuel.

The two center holes are the pump discharge windows and also the air bleed to prevent pump pull over. A pump pullover is when gas is coming out of the discharge when the accelerator pump isn’t being activated.