To enable a petrol engine to accelerate, the mixture must be enriched. This is also the case with vehicles having a regulated catalytic converter. The acceleration equipment has the job of injecting additional fuel for as long as the accelerator pedal is pressed.
In most operational areas, the carburetor functions through vacuum, only when accelerating, do most carburetors, by means of a piston-pump - on the right beside the choke funnel- (top picture) inject additional fuel. The pump is operated by linkage-rods coming from the accelerator pedal (arrow). Thereby, the internal piston first of all takes up the whole stroke, and through it's spring, passes this on to the larger piston. Gravitational ball-valves in the intake- and injection channels prevent a flow-back. In the picture below, the injection occurs through a membrane pump.
In the partial load area, up to about 2/3 of the throttle, most carburetors inject some fuel every time the pedal is pressed. This is why, when driving at an even pace, the pedal should be kept still. 01/11