2G - Manual Choke
2GC - Automatic Choke (choke is mounted directly onto the carb bowl or throttle body)
2GV - Divorced Choke (choke thermostat is mounted in the intake manifold)

IDENTIFICATION

PLEASE NOTE:

2 Jet carburetors manufactured before 1968 did not have stamped numbers, they only came with identification tags.
Carbs manufactured after 1968 are stamped. The number is horizontal on the bowl and stamped into the metal.
Raised numbers or those in a circular pattern are casting codes and won’t cross to kits
Numbers stamped anywhere else on the carb (inside or outside) will not cross to parts

GENERAL DESCRIPTION

There are three basic model G or “2 Jet” Rochester two barrel carburetors. They are they models 2G, 2GC, and 2GV.

The basic model designation is G. The (2) ahead of the G means the carburetor has two bores, two venturii, and two separate but identical metering systems, one for each carburetor bore. The two bore carburetor is normally used on V8 engines where each bore supplies air and fuel to 4 cylinders through a divided intake manifold.

THere are two differen throttle body flanges used on the Rochester two bore carburetors. They are 1 1/4” and 1 1/2”. The flange size used for a particular application is usually determined by the carburetor bore size. Larger engines normally have more air capacity, hence, larger carburetor bores and flanges are needed on these applications.

The Model 2G carburetor is equipped with a manually operated choke valve. Its major applications are on truck and marine engines where an automatic choke is not an absolute necessity.

The Model 2GC carburetor is the basic model 2G unit except the C designates an automatic choke which in this case is an integral part of the carburetor unit. The automatic choke housing and thermostatic coil may be located on the air horn or throttle body, depending upon which application the particular unit is to be used.

The Model 2GV carburetor is also an automatic choke model. However, a vacuum break diaphragm unit is used in place of the conventional choke housing and choke piston. The choke thermostatic coil is located on the engine exhaust manifold and is connected to the choke valve by linkage.

The Rochester two bore carburetor has been kept basically simple for ease in servicing the unit. The major portion of the calibrated metering parts are contained in the venturi cluster assembly. The venturi cluster fits on a flat portion of the carburetor float bowl at the side of the main venturi. The idle tubes and main discharge nozzles are permanently installed in the cluster body by means of a precision pressed fit. The main nozzles and idle tubes are suspended in the fuel in the main wells of the float bowl. This method of assembly and design serves to insulate the main metering parts from engine heat, thus preventing fuel vapors from disrupting efficient carburetor metering during “hot” engine operation.

The main metering jets are a fixed orifice type so that wearing parts can be kept to a minimum. Metering calibration is accomplished through a system of calibrated orifices and air bleeds which supply the correct air/fuel mixtures to the engine throughout all operational ranges. The carburetor float bowl is located so that each system will give instantaneous response for maximum efficiency and performance.

There are six basic systems used in the Rochester model G two bore carbs. They are float, idle, main metering, power, accelerator pump, and choke systems.