The purpose of the float chamber is to maintain a constant fuel level, as it determines the amount of fuel entering with the air. It is also necessary to stop the fuel supply when the engine stops.
The float of a carburetor with a needle valve attached to it, usually of the needle type, maintains a constant fuel level. When the chamber is empty, the float and needle are lowered, allowing fuel to flow unhindered into the chamber from the tank. When the chamber is filled with fuel to a certain level, the float rises and, acting on the firing pin (directly or through a lever), raises it, stopping the fuel supply. The fuel level is adjusted by deflecting the lever that controls the valve or by placing washers under the valve seat.