Carter 4 barrel carbs have had a vacuum operated door, most of them did but not on all of the AFB, on the secondary for along, long time Some of the WCFB had them and most AFB had them, all the AVS and Thermoquad carbs have them , The rear throttle shaft with the butterfly, throttle plates, are mechanical operated off the gas pedal, not vacuum, but the doors above the venture or fuel shafts are vacuum opened
Holley vacuum secondary throttle shafts are opened by a vacuum pod, not the throttle linkage like Carter did. On the Holley vacuum secondary carbs the throttle linkage does close them also along with the primary throttle shafts