Carburetors work by using a venturi, which is a narrowing in the inlet tube, to cause the intake air speed to increase and create a vacuum. This vacuum pulls in fuel from the attached chamber through a hole in the venturi, called a jet.
During starting, when the engine needs a fuel-rich mixture, a choke on the carburetor is closed to lessen the amount of air flowing through and cause the venturi to suck more fuel. During normal use, the flow of air is controlled by the throttle plate. When the accelerator pedal or lever is pulled, the throttle plate opens further, allowing more air to flow in at a faster rate. This pulls in more fuel and allows the engine to produce more power and go faster. Carburetors have a pair of screws, called the high and low valves, that can be adjusted to regulate the amount of fuel flowing at full throttle and idle, respectively. The fuel that flows through the carburetor is taken by a float-feed chamber attached to its side. As fuel is supplied through the carburetor, a float inside the chamber sinks. When the float sinks below a certain level, a valve opens that allows fuel from the main tank to fill the chamber.