Abstract: An apparatus and method of introducing a fluid, as water, alcohol, or a mixture of water and alcohol, into intake air of an internal combustion engine. An electric motor drives a pump that delivers fluid under pressure to a nozzle mounted on the cover of an air cleaner above the air inlet of the carburetor. The electric energy supplied to the electric motor is modulated in a manner to operate the motor so that the pump discharges fluid at a rate that maintains the fluid to air/fuel mixture ratio substantially constant over the operating rpm of the engine. An electric control circuit is operably associated with a diaphragm assembly connected to the intake manifold and a light emitting and reflective light sensing component operable to produce an electric signal response to movement of the diaphragm that is proportional to vacuum pressure in the intake manifold.