Carburetor: Description and Operation

Fig. 1 Exploded view of Rochester Model E2SE 2 barrel carburetor (Part 1 of 2):

Fig. 1 Exploded view of Rochester Model E2SE 2 barrel carburetor (Part 2 of 2):

Fig. 2 Exploded view of Rochester Model 2SE 2 barrel carburetor (Part 1 of 2):

Fig. 2 Exploded view of Rochester Model 2SE 2 barrel carburetor (Part 2 of 2):

The Varajet models 2SE and E2SE, Figs. 1 and 2, are two barrel two stage down draft 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 body to reduce heat transfer.

The primary stage has a triple venturi, with a small 35mm bore, resulting in good fuel metering control during idle and part throttle operation. The secondary stage has a 46mm 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 operating, 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 pre-set at the factory and a plug is installed to prevent further adjustment. The plug should be removed or the screw setting disturbed. If the float bowl is replaced, the replace fuel bowl will include a factory pre-set screw and plugged part throttle screw.

A hot idle compensator is used on some units 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 is open, additional air is allowed to bypass the throttle valves and enter the intake manifold to prevent rough engine idle during period 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 pre-set idle mixture setting. The plug should not be removed or the mixture screw readjusted unless required by major carburetor overhaul or throttle body replacement.

The E2SE carburetor, includes special design features. An electrically operated mixture control solenoid in the air horn, control air/fuel metering 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 ECM 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 the lean position, fuel metering is controlled by a lean mixture screw located in the float bowl. When 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 increase 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 a second, controlling air/fuel mixtures.