Small Engines (Lawn Mowers, etc.): 1 yr old craftman riding mower, stroke oil, craftman

Question
My mower was working fine until i let a neighbor use is, when he brought it back he said it would not start after his son mowed the grass. I put in a new battery, fuse, and when i replaced the spark plug there was black oil around the threads, ( does this mean he put 2 stroke in the mower?) The engine tries to start put it won't kick over the fuel also does look a little dark. Any happy appreciated. Thank you

Answer
Hi Gene,

Sorry for my delay.  It was a busy holiday here.

Maybe a 2 stroke oil was used.  In most cases, an engine will smoke but run okay.  Check the oil level.  Is it getting fuel and good spark?  Check the compression.   

I am swamped with questions and can't give follow up answers until next week.  Sorry.

Good Luck,
Michael