Carburetors are devices that mix air and fuel together in the proper ratio for combustion. They are found in both small engines, like those used in lawnmowers, and in larger ones, like those used in automobiles. The carburetor has several parts that work together to perform this task.
The float is one of the most important parts of the carburetor. It is a hollow chamber that sits on top of the fuel and regulates how much fuel enters the carburetor. The float rises as more fuel is needed and falls as less is needed.
The needle valve controls the flow of fuel into the carburetor bowl from the float chamber. When the engine is turned off, the needle valve closes and prevents fuel from flowing into the bowl. When the engine is started,the needle valve opens and allows fuel to flow into the bowl .
The main jet supplies most of the fuel to be mixed with air when operating at full throttle. The idle jet supplies a smaller amount of fuel for operation at idle speed or low throttle settings. Both jets are located in the carburetor body below the bowl .
The choke restricts airflow throught he carburetor when starting a cold engine to enrich he mixture for easier starting . it also provides some enrichment at higher altitudes where thinner air requires a richer mixture for good performance . The choke is usually operated manually by a lever on he dash or steering column but may be automatic on some models .