Trouble starting Craftsman Lawn Tractor Mod#...

Question

Tractor won't start. Will not turn over. Put in new battrey and chaecked all wires, no corrosion. Read somewhere that it couod be commpression proeblem. I removed the spark plug and engine cranks fine. Replace spark plug and engine started and ran great (had to plow snow). I tried it again today and it wouod not start. I again removed the spark plug & this time gas poued out of the spark plug hole. Replaced and engine ran good and plowed this next round of snow. What could be causinf this problem. Engine has been hard to start since day one (about 8 years) but I was ussually able to get it to start.