I have a 2yr old honda HRX mower that the spark plug is turning black within minutes of me cleaning it off. It runs horribly and I have changed the oil, spark plug and gas. It seems to be burning tons of fuel at a rapid pace and it also is very sluggish and the self propel seems to be much much slower then it was when I purchased this thing. This mower has not lived up to what it is supposed to be. Any suggestions on what I can do to fix this thing would be great.