Is the plug wet after you try to start it?  
I know that a Banshee will start without pipes, albeit not very easily.  If you have even a remotely sealed engine and are getting fuel, pouring gas in the engine will only foul a plug.  Can you tell us about how your carb is set up?  Napa sells carb cleaner for $3.00 IIRC.  I get every can they have when it goes on sale for $1.50.  
Is the spark bright blue?  Also, great spark at the wrong time is effectively useless, so I'm with wife's blaster on this one.  Check to see if the key is sheared.  
I also agree with Wife's Blaster on you taking a step back.  Get back to the basics.  CORRECT Spark, fuel, air, compression.  Anything that you check or fix is one more thing that you know isn't the problem.