The effects of excess feeding oxygen to the fuel-air mixture on air and fuel mass flow rates and also on air-fuel ratio are investigated here experimentally. This study concerned with the effects of injecting pure oxygen quantity to the mixture of fuel and air before interring the combustion chambers. It is found that the mass flow rate of fuel with the oxygen feeding is less than that of with no oxygen feeding at some specific values of engine speeds and the same thing was found for air mass flow rate. The air-fuel ratio also is less with considerable values in the case with oxygen feeding than that with no oxygen samples. Also this technique can be used partially, in some conditions oxygen can be feed into the combustion chambers to increase engine performance.