Clean the spark plug first. then You possibly need to adjust the mixture while the mower is running, this is done by a small screw at the front of the carb, just below the black metal support bar. Make sure your hands are off the ground as you could easily loose you fingers if you slip. Turn the screw a 1/4 turn anticlockwise at a time and leave for a few seconds, keep count of the times you move the screw so you can reset if needed. keep going until the motor speeds up and runs smooth, if you go to far the motor will stop as it will flood the engine. The screw will come right out after about 4 turns, if that doesnt speed up the engine after 3 turns, that means that the fuel system is blocked somewhere and will need a strip down.....good luck....
Alan, April 2013