Tell me if the plug looks wet or dry to begin with. Along the lines of what CD says, how long did it sit? Sounds very much like a fouled plug, happens frequently when someone rebuilds, probably puts way more oil on everything than they should, and lets it idle.
LOL, it used to be that if your bike died, the first thing you do is check for spark, ie plug etc. Now you LOGON!! Don't worry about the crankshaft after all