Holley Two-Barrel Carburetor Tunable Metering Block Photo Gallery
This anti-siphon air bleed breaks the siphoning vacuum pulled on the accelerator pump passage. It stops unmetered fuel from being sucked into the venturis from the pump discharge nozzles at WOT and richening the mixture. It comes stock at 0.020-inch. Note the reinforcing ribs of the adjustable metering block to add strength.