Introduction

A new carburetor was designed for smaller engines. The two-stage carburetor, built almost entirely of aluminum, first came out on GM front-wheel-drive vehicles. The Varajet would serve all GM divisions (see usage chart at the end) using the 2.5-liter four-cylinder and the 2.8-liter V6 until throttle body and port fuel injection technology made conventional carburetors obsolete. It was also used on the 1.8L four cylinder engines, and by the Holden division of General Motors (Australia).

The first model (1979) 2SE didn't have a Computer Command Control (CCC) system with a mixture-control solenoid and electronic idle-speed control. It was introduced as a conventional downdraft carburetor. The electronics were added within two years.

Why did RPD (Rochester Products Division) go to the expense of designing a new model for small engines when they already had the Monojet with its good track record? For the same reasons the Dualjet replaced the 2G - the idle, off-idle and main system metering couldn't be controlled enough to meet emission and economy standards. If the Monojet were downsized enough, and the venturi made sensitive enough to meet emission and fuel-economy standards, It would have been too small to deliver adequate HP.

The Varajet models 2SE and E2SE, Figs. 1 and 1A, 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.

Rochester Varajet 2SE picture from Motor Manual (ISBN: ) This one would be figure 1.

Rochester Varajet E2SE picture from Motor Manual (ISBN: ) This one would be figure 2.

The 2SE two-stage was designed with a triple-venturi 35mm primary bore for fuel metering control during idle and part-throttle operation. That bore was too small to expect any reasonable HP, so a 46mm secondary bore was added. This design supported the power requirements at heavy throttle.

An air valve is used in the secondary stage with a single tapered metering rod. Metering control is governed by the air-valve opening so a suitable power mixture prevails regardless of how far open the secondary is.

The float chamber is internally vented though 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 pre-set 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 pre-set 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 pre-set mixture setting. The plug should not be removed and the mixture screw readjusted unless required by major carburetor overhaul or throttle body replacement.

Another feature of the 2SE is its low-profile design. On modern cars, engine compartments are smaller and hood lines lower, so tall units are out of the question.

The E2SE carburetor, includes special design features for use with the Computer controlled Catalytic Converter System (C4) or the Computer Command 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 form the oxygen sensor in the exhaust and other engine operating 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 decreased 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.

On 1981 models with 4-151 engine and air conditioning and 1982 models with 4-112 (1.8L) engine, an idle speed control motor which is controlled by the Electronic Control Module is used to control idle speed, Fig. 1B. The curb idle speed is programmed into the Electronic Control Module and no attempt should be made to adjust idle speed using the idle speed control motor.

CAUTION: On 1980-83 units, use care not to remove the special friction reducing coating applied to the primary and secondary throttle shafts, the secondary actuating lever and lockout lever. On 1980 V6 units and on all 1981-83 units, a special graphite compound is also applied to the secondary throttle bore and valve.

Carburetor Usage