Sounds like it is either flooding the cyl. or it is firing speraticlly allowing excess fuel to build up in the exhaust. Take Chy up on his offer, very hard to diagnose things just on a description. I know how I would approach the problem but it would take pages of text to explain what I would do and in what order and the problem could be at any given point in the diagnosis process.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!