Carter carburetion and Mopars are synonymous. Performance Mopars from the musclecar years almost always came topped with a Carter to provide the fuel mix. In the height of the musclecar years, the most common Mopar four-barrel carb was Carter's AVS. Although the earlier AFB was fitted to the Hemi, the AVS was a significant refinement of the AFB design. We say refinement because although the AVS was a new design, the similarity to the AFB was obvious. It was so similar, in fact, that the AVS never achieved the same widespread recognition in the performance world as the AFB because, to the casual observer, the AVS was often mistaken for an AFB.

In the AVS, the most notable departure from the AFB design was in the actuation of the secondary. The AFB carb was conventional in the secondary circuit in that it used a conventional booster venturi configuration to deliver the secondary fuel flow. The secondary throttle plates were mechanically operated. In order to provide for a smooth transition into the secondary circuit (without the benefit of a secondary accelerator pump circuit), a counterweighted velocity valve was installed above the throttle plates. The velocity valve acted as an auxiliary to the throttling system, delaying the airflow through the secondaries until engine demand overcame the counterweight and allowed the valve to open. The delay in airflow slowed the progression into the secondary circuit, allowing the airflow through the secondary booster venturi to start drawing fuel.

The goal was to provide enough of a delay in air flow to prevent a lean bog as secondary airflow is suddenly initiated by mashing open the throttle. The system worked, but it had two flaws. First, the positioning of the velocity valve is above the throttle plate and below the discharge nozzles. Besides delaying airflow, this offers little help in initiating fuel flow through the booster. Second, the system was not readily adjustable to vary the opening rate.

In contrast, the AVS carb--designated for its Air Valve Secondary--was quite a departure from convention at the time of its introduction. The counterweighted velocity valve of the AFB was scrapped, and a spring-loaded air door was fitted at the top of the carb. Positioned above the fuel-discharge point, the air valve created a depression, or low-pressure area at the fuel-discharge point. This dramatically increased the reaction rate of the secondary fuel circuit. The function of the AVS's air valve in drawing fuel flow was advantageous compared to the old AFB system's function of simply delaying airflow. The system was so effective that a conventional booster venturi wasn't needed, and AVS carbs were fitted with fuel spray bars, which complemented the air valve perfectly. To cap things off, the spring-loaded air door was easily adjustable for opening rate by simply loosening a lock screw and winding the spring tension on the valve's shaft.

AVS carburetors were factory-fitted by Chrysler in some of the most popular musclecars, from 383 Road Runners and Super Bees, to 340 Darts, Barracudas, and Dusters. And let's not forget the 440 Magnum-equipped B- and E-Bodies from the peak of the glory days. In fact, take your pick of 340, 383, and 440 high-performance four-barrel engines, and with the exception of some 383s in 1970-'71, you'll find an AVS on top.

We recently found a fine '70 340 AVS carb collecting dust on a salvage-yard shelf and had to have it. These carbs are remarkably rugged and easy to rebuild. Ours had accumulated a lifetime of dirt and grime, but with a $24 rebuild kit and a day's work, it was functioning as good as new.

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