Weird...cam problem maybe?
The first thing that comes to mind is you might have had some bacon caught in one of the valves holding it open or the spark plugs were bacon fouled.
Seriously, i do think it was carb icing due to some crappy gas, and i also have had the plugs foul a lot on my /6 when i ran into some lousy gas mainly on #6 for some reason.
Maybe it's because it's the farthest cyl from the carb.