When the engine comes from slow to high running speed, at that . time petrol in adequate quantity does not reach from the main nozzle. In order to provide more petrol to the mixture, an accelerating pump is provided. Besides this, whenever the quantity of petrol is to be increased in the mixture for example, at the starting time, we can increase the quantity of petrol from this Automobile Engineering . pump which is fixed in the float chamber of carburettor itself by … pressing the accelerator pedal several times.