Operating principle of the Pierburg 2E2 carburetor (VW Passat B2)

The design features and calibration data of the carburetor are given in the subsection "Design and technical characteristics".

Starting device

Under the action of the thermostatic bimetallic spring of the automatic starting device, the air damper 1 (see diagrams) blocks the air supply to the carburetor duct. The throttle valve 2 of the 1st chamber is held in the slightly open position simultaneously by the three-nozzle pneumatic actuator 3, the rod 4 of which is retracted by the spring from the stop of the throttle valve of the 1st chamber, and the thermal power element 5 of the liquid heating system of the starting device, acting on the cam for opening the throttle valve of the 1st chamber. Due to the slightly opening of the throttle valve of the 1st chamber, a significant vacuum is created in the main metering system of the 1st chamber, which is necessary for starting a cold engine and increasing the crankshaft speed at idle (see diagram "A").

After starting the engine, the vacuum that occurs in the intake manifold acts on the pneumatic actuator 6 (see diagram "B"), which slightly opens the air damper. With the transition to the operating mode, the rods, driven by the throttle valve of the 1st chamber, open the air damper, as a result of which the fuel-air mixture becomes leaner and uninterrupted operation of the engine is ensured.

Idle and transition system

After the engine is started, the time relay thermal valve closes the connection between the pneumatic drive 3 of the throttle valve of the 1st chamber and the atmospheric air, and its rod returns to the position corresponding to the idle speed of the warmed-up engine. During engine warm-up, the throttle valve of the 1st chamber is held in a slightly open position due to the smooth heating of the thermal power element of the liquid heating system of the automatic starting device.


Fuel from the float chamber enters through the main fuel jet 7 into the emulsion tube well and the idle jet. Fuel mixes with air entering through the opening regulated by the screw 2 of the mixture quality (composition). The fuel-air mixture exits under the throttle valve through the slot 10 of the idle and transition system, which leads to a gradual increase in the engine crankshaft speed.

The transition system of the 2nd chamber operates in a similar manner, ensuring an increase in the crankshaft rotation frequency as the throttle valve of the 2nd chamber opens.

Main dosing system

Fuel through a needle valve, the flow area of which is regulated by a float, fills the float chamber and is held here at a constant level. The needle valve is connected to the float tongue by a hook.

From the float chamber, under the action of vacuum, the fuel enters the well of the emulsion tube through the main fuel jet 7 (see diagram) of the 1st chamber, where it mixes with the air coming out of the opening of the main air jet 12. The resulting emulsion is sprayed by the air flow passing through the small and large diffusers 13.

The main metering system of the 1st chamber includes a power mode economizer. When the vacuum in the area of the throttle valve 2 of the 1st chamber drops, caused by a significant opening of the throttle valve, there is no vacuum in the diaphragm cavity of the housing of the power mode economizer 14, the valve 15 of which, under the action of the spring, opens the channel 16 for supplying additional fuel to the fuel jet of the main metering system of the 1st chamber.

The main dosing system of the 2nd chamber operates similarly, in which an economizer is included instead of a power mode economizer. Enrichment of the fuel-air mixture in the full load mode in the 2nd chamber is ensured by spraying under the action of a strong vacuum of pure fuel through the injection tube 17 of the economizer, the outlet of which is located above the mixture formation zone.

Accelerator pump

When the throttle valve 2 (see diagram) of the 1st chamber is opened, the cam 18 actuates the lever 19 of the accelerator pump drive and the pump 20 pumps the fuel sucked from the float chamber into the mixture formation zone through the check valve and the sprayer 21.