Carburetor: Description and Operation

Fig. 2 Exploded view of Rochester Varajet 2SE carburetor:

Fig. 3 Exploded view of Rochester Varajet E2SE Carburetor (Part 1 of 2):

Fig. 3 Exploded view of Rochester Varajet E2SE Carburetor (Part 2 of 2):

The Varajet models 2SE and E2SE, Figs. 2 and 3, are two barrel, two stage, down draft design carburetors. Aluminum die castings are used for the air horn, float bowl and throttle body. A heat insulator gasket is used between the throttle body and float bowl to reduce heat transfer to the float bowl.
The primary stage has a triple venturi, with a small 35 mm bore, resulting in good fuel metering control during idle and part throttle operation. The secondary stage has a 46 mm bore, providing sufficient air capacity for engine power requirements. An air valve is used in the secondary stage with a single tapered metering rod.
The float chamber is internally vented through a vertical vent cavity in the air horn. The float chamber is also externally vented through a tube in the air horn. A hose connects this tube directly to a vacuum operated vapor vent valve located in the vapor canister. When the engine is not running, the canister vapor vent valve is open, allowing fuel vapor from the float chamber to pass into the canister where the vapor is stored until normally purged.
An adjustable part throttle screw is used in the float bowl to aid emission control. This screw is factory preset and a plug is installed to prevent further adjustment or fuel leakage. The plug should not be removed or the screw setting disturbed. If float bowl replacement is required, the service float bowl will include a factory preset and plugged adjustable part throttle screw.
A hot idle compensator is used on some models and is located in the air horn. The opening and closing of the hot idle compensator valve is controlled by a bi-metal strip that is calibrated to a specific temperature. When the valve opens, additional air is allowed to bypass the throttle valves and enter the intake manifold to prevent rough idle during periods of hot engine operation.
The idle mixture screw is recessed in the throttle body and is sealed with a hardened steel plug to prevent alteration of the factory preset mixture setting. The plug should not be removed and the mixture screw readjusted unless required by major carburetor overhaul or throttle body replacement.
The E2SE carburetor includes special design features for use with the Computer Controlled Catalytic Converter (C4) System or the Computer Command Control (C3) System. An electrically operated mixture control solenoid, mounted in the air horn, controls air and fuel metered to the idle and main metering systems of the carburetor. The plunger located at the end of the solenoid is submerged in fuel in the fuel chamber of the float bowl. This plunger is controlled by an electrical signal from the Electronic Control Module (ECM). The Electronic Control Module responding to signals from the oxygen sensor in the exhaust and other engine operating condition signals, energizes the solenoid to move the plunger down to the lean position or de-energizes the solenoid to move the plunger up to the rich position to control fuel delivery to the idle and main metering systems. When the plunger is in the lean position, fuel metering is controlled by a lean mixture screw located in the float bowl. When the plunger is in the rich position, the additional fuel is metered to the main fuel well through a rich mixture screw located at the end of the fuel supply channel in the float bowl. Air metered to the idle system is controlled by the up and down movement of the mixture control solenoid plunger. The plunger increases or decreases air supplied to the idle system which is further metered by the idle air bleed screw. The plunger cycles up and down approximately 10 times per second, controlling air and fuel mixtures.