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.