Conversion of CH4 with a N2 microwave plasma (2.45 GHz) is studied. The experiments cover the absorbed microwave power range 300-700 W with 17-62% of methane in the gas mixture, with pressures of 10-40 mbar and flow rates of 140-650 ml.min-1. The yields of C2 hydrocarbons and dihydrogen are analyzed by gas chromatography. The distance of methane addition downstream of the plasma plays an important role on the composition and the concentration of the products obtained This distance mainly determines the energy concentrated in the active specks of the plasma when they react with methane. Different behaviors for acetylene formation, on the one hand, and for ethane and ethene formation, on the other hand, have been observed, and this finding allows us to propose a kinetic mechanism for the decay of methane and for the formation of C2 hydrocarbons.