Carter carburetion and Mopars are synonymous. Performance Mopars fromthe musclecar years almost always came topped with a Carter to providethe fuel mix. In the height of the musclecar years, the most commonMopar four-barrel carb was Carter's AVS. Although the earlier AFB wasfitted to the Hemi, the AVS was a significant refinement of the AFBdesign. We say refinement because although the AVS was a new design, thesimilarity to the AFB was obvious. It was so similar, in fact, that theAVS never achieved the same widespread recognition in the performanceworld as the AFB because, to the casual observer, the AVS was oftenmistaken for an AFB.
In the AVS, the most notable departure from the AFB design was in theactuation of the secondary. The AFB carb was conventional in thesecondary circuit in that it used a conventional booster venturiconfiguration to deliver the secondary fuel flow. The secondary throttleplates were mechanically operated. In order to provide for a smoothtransition into the secondary circuit (without the benefit of asecondary accelerator pump circuit), a counterweighted velocity valvewas installed above the throttle plates. The velocity valve acted as anauxiliary to the throttling system, delaying the airflow through thesecondaries until engine demand overcame the counterweight and allowedthe valve to open. The delay in airflow slowed the progression into thesecondary circuit, allowing the airflow through the secondary boosterventuri to start drawing fuel.
The goal was to provide enough of a delay in air flow to prevent a leanbog as secondary airflow is suddenly initiated by mashing open thethrottle. The system worked, but it had two flaws. First, thepositioning of the velocity valve is above the throttle plate and belowthe discharge nozzles. Besides delaying airflow, this offers little helpin initiating fuel flow through the booster. Second, the system was notreadily adjustable to vary the opening rate.
In contrast, the AVS carb--designated for its Air Valve Secondary--wasquite a departure from convention at the time of its introduction. Thecounterweighted velocity valve of the AFB was scrapped, and aspring-loaded air door was fitted at the top of the carb. Positionedabove the fuel-discharge point, the air valve created a depression, orlow-pressure area at the fuel-discharge point. This dramaticallyincreased the reaction rate of the secondary fuel circuit. The functionof the AVS's air valve in drawing fuel flow was advantageous compared tothe old AFB system's function of simply delaying airflow. The system wasso effective that a conventional booster venturi wasn't needed, and AVScarbs were fitted with fuel spray bars, which complemented the air valveperfectly. To cap things off, the spring-loaded air door was easilyadjustable for opening rate by simply loosening a lock screw and windingthe spring tension on the valve's shaft.
AVS carburetors were factory-fitted by Chrysler in some of the mostpopular 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 of340, 383, and 440 high-performance four-barrel engines, and with theexception 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 asalvage-yard shelf and had to have it. These carbs are remarkably ruggedand 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 goodas new.
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