holley carbs

On the carter the secondaries won't pull fuel until the air door is open. The throttle plates (the ones in the bottom of the carb) are what is mechanical. Ya can't make a Carter a full mechanical secondary carb. The closest you can come to that would be (on an AVS) to remove all tension from the air valve spring or (on an AFB) break down the carb, remove the air valve assembly and remove weight from, or entirely remove the counterweight(s)