Zenith carburetor is the most popular carburetor used in modem automobiles. It consists of a jet, throttle valve, venturi, choke, adjusting knob, float chamber etc., as shown in below figure 1.
Figure 1: Zenith Carburettor.
There are three different type of jets namely main jet, idling jet and compensating jet. Initially, the carburettor choke valve is used to start, whereas for an idling condition, the throttle valve is made to close. The suction is applied to the idling jet. which supplies fuel to the engine. The air is allowed through holes provided near idling jet. An idle adjust knob is provided to control the air through holes. The air is then passed through the passage provided near the idle adjustment knob. The throttle valve is opened partially for supply of air mixture to the venturi. During this air flow, the main jet and idling jet supplies the air mixture. Further, when the throttle valve is opened. the complete suction is carried to the main and compensating jets. where proper amount of air fuel mixture is carried for different speeds of engine.