ROCHESTER B, BC, AND BV CARBURETOR IDENTIFICATION
There are three main types of the Rochester B carburetors, identified by their choke style.
The basic Model B carburetor is a single bore downdraft type. It is equipped with a manually operated choke and is mainly used on truck applications.
The model BC is the same basic unit except it has a fully automatic choke mounted on the air horn and is used for both passenger car and truck applications.
The model BV unit uses a fully automatic choke, however, instead of a conventional choke piston and housing, a vacuum operated diaphragm plunger (choke pull-off) is used. The thermostatic coil is mounted on the exhaust manifold instead of the choke housing and is connected to the caburetor choke shaft by a connecting linkage.
Design features included in all of the above carburetor models are as follows:
A concentric type float bowl is used which allows fuel in the float bowl to completely surround the main carburetor bore and venturi. The concentric float bowl design plus the centrally located main fuel discharge nozzle prevents fuel spill-over during abnormal car maneuvers such as sharp turns and quick starts and stops. Unfortunately due to the bolt design and overtightening, Rochester B series carbs are notorious for having warped bowls which will allow fuel to splash around inside the bore and cause the carb to cut out on hard stops and turns.
The main assembly is a detachable unit which contains the main metering parts of the carburetor. It is attached to the air horn and is easily removed for inspection and service. It is suspended in the fuel in the float chamber which insulates it from heat which may be transmitted from the engine directly to the bottom of the float bowl. This type design helps maintain more accurate fuel metering because less fuel vapors enter the main metering parts of the assembly, during hot engine operation.
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Rochester B:
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Used mainly on early Chevrolet 6-cylinder engines (1949-1962).
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Manual choke (sometimes cable-operated).
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Common on vehicles like early Chevy Bel Air, 210, and trucks.
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Rochester BC:
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Variant of the B with an automatic choke (uses a heat tube from the exhaust).
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Installed on similar 6-cylinder engines but often found in slightly more upscale models or those requiring easier cold starting.
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Rochester BV:
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"BV" indicates further changes, often including a vacuum break (hence "V").
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Used mostly in trucks and heavy-duty applications.
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Improved cold-start operation compared to the B and BC.
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