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Device for supplying a spark-ignition engine with a mixture of fuel and air. Carburetors are used in small gasoline engines, such as lawn mowers and chainsaws. Once an essential component in all gasoline engines, automobile carburetors were displaced by electronic fuel injection systems from the late 1970s through 1990. Carburetors for automobile engines usually contained a storage chamber for liquid fuel, a choke, an idling jet, a main jet, an airflow restriction, and an accelerator pump. The quantity of fuel in the storage chamber was controlled by a valve actuated by a float. The choke, a butterfly valve, reduced the intake of air so that a fuel-rich charge was drawn into the cylinders when a cold engine was started. As the engine warmed up, the choke was gradually opened. Reduced pressure near the partially closed throttle valve caused the fuel to flow from the idling jet into the intake air. Further opening the throttle valve activated the main fuel jet. Then the venturi-shaped airflow restriction created reduced pressure, drawing fuel from the main jet into the airstream at a rate related to the airflow so that a nearly constant fuel-air ratio was obtained. The accelerator pump injected fuel into the inlet air when the throttle was opened suddenly. See alsogasoline engine; venturi tube.
This entry comes from Encyclopædia Britannica Concise. For the full entry on carburetor, visit Britannica.com.