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Rebuilding the Carter AFB Carburetor

The basics on restoring carburetor performance

Steve Dulcich Nov 7, 2016
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The Carter AFB carburetor was introduced in 1957, and the same basic design lives on to this day as an Edelbrock-manufactured variant. For any mechanical device to remain in production for nearly 60 years is testimony to fine design work and functionality. It also means that countless examples of these carbs can be found—many in need of basic refurbishment. While a carburetor is not particularly difficult to rebuild, there’re many performance enthusiasts who shy away at the thought of disassembling and rebuilding, often choosing to simply buy a replacement instead.

In the world of Corvettes, the Carter AFB four-barrel carburetor was synonymous with the Vette powerplant from its beginnings in 1953 on the six-cylinder through 1965 on the 327 when the Carter was discarded in favor of the Holley. In 1965, the Carter was used on the 250- and 300hp V-8s both on automatic and manual transmission cars. The 350- and 365hp small-blocks and the big-block used the Holley. Holley did appear in 1964 on the 365hp 327 while the Carter did appear on the 250- and 300hp V-8s.

Rebuilding a carb is actually a fairly quick and easy process that requires little more than a few basic tools, a cleaner, and a carburetor kit. Before the advent of fuel injection in performance vehicles, rebuilding the carb was a routine procedure, performed in garages and backyards across the country. These days, few of us have a carbureted vehicle serving as daily transportation, but a vast majority of hot rods, race cars and weekend toys still use carbs. As a simple mechanical device, a carb is reliable, relatively cheap and long lasting. For the most part there is little to wear out, but dirt, debris and deposits can take a toll, even rendering a carb inoperative. A carb kit will include the typical wear components, as well as new gaskets and seals. We had a 750-cfm #6212S carb off a jet boat application, along with a Walker 15271A kit. This is how they went together.

Carter Afb Four Barrell Carburetor 2/14

01. Our #6212 Carter AFB is a 750-cfm unit for a marine application. The carb has been on duty since the early 1970s and will be good for decades to come with a simple rebuild.

Carter Afb Four Barrell Carburetor Castings 3/14

02. The AFB design is ingeniously simple, being constructed from just two major castings—the main body and the air horn. Step one any time an AFB is opened is to remove the metering rod assemblies.

Carter Afb Four Barrell Carburetor 4/14

03. To separate the carb, remove all of the external linkages, then the screws retaining the air horn. Sometimes the air horn gasket can be stuck. To break it loose, use penetrating oil and tap the periphery with a hammer. Avoid prying on the air horn.

Carter Afb Four Barrell Carburetor 5/14

04. There are very few parts in the air horn assembly. We find the needle and seats, floats and fuel inlet.

Carter Afb Four Barrell Carburetor Fuel Distribution Tabs 6/14

05. These odd fuel distribution tabs are found on the secondary boosters.

Carter Afb Four Barrell Carburetor Parts 7/14

06. As can be seen here, the main body carries the majority of the AFB’s parts, including the jets. Clockwise from lower left we have the choke dashpot, right primary booster, secondary boosters, velocity valve, left primary booster, accelerator pump pistons and spring, accelerator pump discharge nozzles and check needle and the idle mixture screws.

Chem Dip Carburetor Cleaner 8/14

07. The best way to clean a carb is by full emersion in a cleaning media. Beware that highly alkaline or caustic cleaners can severely discolor and corrode aluminum, and strip the plating from the steel parts. Likewise, highly acidic cleaners will have similar detrimental effects. We used a bucket of carburetor cleaner. Other options include the use of sonic cleaning equipment.

Carter Afb Four Barrell Carburetor Parts 9/14

08. Once the parts are cleaned, thoroughly rinsed and blown dry with compressed air, we like to lay everything out neatly in order. This helps inventory the parts and minimizes the potential for omissions or assembly errors. We also liberally spray all of the parts with a lubricating and protecting penetrating oil.

Spraying Gaskets 10/14

09. Spraying the gaskets and sealing rings with penetrating oil will prevent them from sticking, making future disassembly easier with less risk of tearing a gasket.

Accelerator Pump Plunger 11/14

10. The accelerator pump plunger for this model of AFB uses a leather seal. Soak the seal in motor oil to soften the material prior to installation.

Air Horn Carter Carburetor 12/14

11. Rebuilding is simple and straightforward. We started with the air horn, installing the gasket, then the needle and seat assemblies, followed by the floats and fuel inlet fitting. Carefully adjust the floats level and float drop to specifications.

Carter Afb Four Barrell Carburetor 13/14

12. Although the main body contains many more parts than the air horn, assembly here is, again, very straightforward. Install the secondary velocity valve, booster venturi, accelerator pump parts, and idle mixture screws and it is done.

Carter Afb Four Barrell Carburetor 14/14

13. Finish by mating the air horn to the main body and reinstalling all of the external linkages. Pay particular attention that the linkages are installed and adjusted properly. We see mistakes related to external linkages as one of the most common sources of a poorly operating carburetor.

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