Operating principle of the Pierburg 1B3 carburetor (VW Passat B2)

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

Starting device

When starting a cold engine, under the influence of the thermostatic bimetallic spring of the automatic starting device, the air damper blocks the air flow through the carburetor duct, the throttle valve 3 (see diagram) under the influence of the system of rods and cams 2 of the drive opens slightly, ensuring an increase in the rotation speed of the cold engine at idle.

Under the action of the vacuum in the diaphragm cavity of the starting device, an increased amount of fuel passes through the main fuel jet, which ensures the starting of a cold engine.

After starting the engine, the vacuum that occurs in the intake manifold of the running engine activates the pneumatic actuator 4, which opens the air damper. After warming up with the transition to the load mode, the air damper opens through a system of rods and levers, driven by the throttle valve, which causes depletion of the combustible mixture and ensures uninterrupted operation of the engine.

Idle and transition system

Fuel taken from the float chamber enters the emulsion tube well through the main fuel jet 5 (see diagram) and is fed to the idle fuel jet 6. At the outlet of jet 6, the fuel is mixed with air entering through the idle air jet. The emulsion is fed to the outlet opening 7 of the idle system under the throttle valve through the opening regulated by the needle screw 8 of the mixture quality (composition), and through the opening closed when the ignition is turned off by the electromagnetic shut-off valve 9.



When the throttle valve 3 is smoothly opened, the combustible mixture enters the vertical channel of the transition system 10, which leads to a gradual increase in the rotation frequency of the engine crankshaft.

Main dosing system

Fuel is supplied to the float chamber through a needle valve. The float, hinged on the axis, regulates the opening of the needle valve hole to maintain a constant fuel level in the float chamber. There is a damping device between the needle valve and the float tongue.

From the float chamber, the fuel enters the emulsion tube through the main fuel jet 5 (see diagram), where it mixes with air passing through jet 11. Then the fuel-air mixture fills the mixing chamber formed by the small and large diffusers 12.

The carburetor has an economizer, which additionally enriches the fuel-air mixture at full engine load at speeds close to maximum. From the float chamber, the fuel passes through the channel and through the jet 13 enters the fuel tube, in the upper part of which it mixes with air entering through the air jet 14. The resulting emulsion passes through the check valve 15 and is ejected through the injection tube 16 into the mixing chamber, additionally enriching the combustible mixture, ensuring engine operation at increased speeds.

Accelerator pump

Under the action of lever 17, the throttle valve opens, spring 18 turns cam 19, which acts on lever 20 of the accelerator pump drive. The lever presses piston 21, which pumps fuel coming from the float chamber through check ball valve 22 to sprayer 23.

The cam drive spring 18 dampens the force of the abrupt opening of the throttle valve, which increases the duration of fuel injection. The position of the cam drive spring on the throttle valve axis is adjustable. In the piston well there is a sealing cuff 24 and a return spring 25. The damper spring 26, located in the cavity of the piston itself, serves to regulate the movement of the piston depending on the amount of fuel passing through the atomizer.