acceleratorpump

An accelerator pump is a component found in many gasoline-powered internal combustion engines, particularly those equipped with carburetors. Its primary function is to enrich the fuel-air mixture temporarily during rapid throttle openings. When the throttle is suddenly opened, the airflow into the carburetor increases dramatically, but the fuel flow lags behind due to inertia. This momentary lean condition can cause hesitation, stumbling, or a flat spot in acceleration.

The accelerator pump compensates for this by squirting a small amount of extra gasoline directly into the carburetor's venturi. This additional fuel helps to bridge the gap until the main metering system of the carburetor can adequately respond to the increased airflow. The pump typically consists of a diaphragm or piston that is actuated by the throttle linkage. As the throttle is opened, the linkage moves a lever or rod, which in turn operates the diaphragm or piston. This action forces a small volume of fuel from a dedicated reservoir within the carburetor through a small nozzle and into the carburetor's airstream.

The amount and duration of the fuel shot are carefully calibrated to provide smooth acceleration without making the mixture excessively rich, which could lead to poor fuel economy or fouled spark plugs. In engines with fuel injection systems, a similar function is achieved electronically by the engine control unit (ECU) adjusting injector pulse width during throttle transients. The accelerator pump is a purely mechanical device, a simple but effective solution to a common characteristic of carburetor operation.