Small Engines (Lawn Mowers, etc.): oil on spark plugs, worn piston rings, toro snow blower

Question
I have a toro snow blower with a b&s 8 hp engine model 190402 type 0755-07.  After sitting this winter, I cleaned the carbs and cranked up.  While readjusting the carbs, the engine stalled out.  I pulled the spark plug and saw significant oil (enough to squash the spark).  I've heard that this is typically attributable to worn piston rings, cyclinder heads, gaskets, or valves.  How do I determine which is the culprit?  I opened to access the piston & valves and hoped that by looking at it I'd have a clue, but there was a lot of black (I imagine some carbon and some oil).  How do I figure out what to replace, and how do I remove the guilty part?  

Here's a link of what it looks like.  

http://www.youtube.com/watch?v=ueCHTNFvZOk

Answer
Hi Al,

I watched your YouTube presentation, and it was well-done.  

Nice job of showing me the built up carbon on the top of the piston and on

the valves.  That carbon build up can be removed with the help of a steel brush,

and this will assist with the operation of the motor.

As far as the initial question you'd asked about the oil on the plugs-

did you check the oil level, ensuring that it is not overly filled?

You might want to overhaul the carburetor completely.  It helps if you have a good manual for this.

I suppose it could be worn piston rings.

Anyhow check those items out and let me know.

Good Luck,

Howard