Carburetor

The carburetor, carburettor, or carburetter also called carb, A device that controls the power output and fuel feed of internal combustion spark-ignition engines used for automotive, aircraft, and auxiliary services.

Its duties include control of the engine power by the air throttle; metering, delivery, and mixing of fuel in the air stream; and graduating the fuel-air ratio according to engine requirements in starting, idling, and load and altitude changes. The fuel is usually gasoline or similar liquid hydrocarbon compounds, although some engines with a carburetor may also operate on a gaseous fuel such as propane or compressed natural gas. A carburetor may be classified as having either a fixed venturi, in which the diameter of the air opening ahead of the throttle valve remains constant, or a variable venturi, which changes area to meet the changing demand.

Carburetor from car engine

A simple updraft carburetor with a fixed venturi illustrates basic carburetor action. Intake air charge, at full or reduced atmospheric pressure as controlled by the throttle, is drawn into the cylinder by the downward motion of the piston to mix with the unscavenged exhaust remaining in the cylinder from the previous combustion. A cylinder is most completely filled with the fuel-air mixture when no other cylinder is drawing in through the same intake passage at the same time. The fuel is usually metered through a calibrated orifice, or jet, at a differential pressure derived from the pressure drop in a venturi in the intake air passage.

Elements that basically determine air and fuel charges received by the engine through the carburetor.

A combustion engine requires a fairly precise mixture of fuel and air to run properly. If too little fuel is introduced into the mix, the engine will either fail to operate or have to strain excessively to do so, wearing it down and possibly resulting in damage. Conversely, if too much fuel is introduced, the engine may flood and fail to operate, or else work in fits and starts. It may also cause the engine to produce an inordinate amount of smoke, and will, if nothing else, unnecessarily squander fuel. Thus, the task of the carburetor is to balance these two extremes by inserting just the right amount of fuel into the engine’s chamber.

cross section of a carburetor

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