An air filter is treated with a reactive functional organosilixane composition so as to increase the oxygen concentration in air drawn through a carburetor system of an internal combustion engine and is also directed to the method of treating a standard air filter of cellulosic material by intermixing an organosiloxane and metal salt catalyst with a volatile solvent, applying the solution in liquid form to the filter and draining and drying the filter until the solvent is evaporated on the surface of the filter.