First, an anecdote:

Last winter met with some 6X6ers in WY for some snow fun. Unloaded an my machine was running really bad. Tim (Obsessed) tossed a tiny bit of snow on the exhaust pipes and showed that the back cylinder wasn't running. He checked the spark plug wire. I put my hand down in to follow the circuit just to see what was down there and all of a sudden it started working again. It hadn't faltered like this before and hasn't since. When I got home I tried to get it to do it again. No joy.

Forward to today. I thought I would try again and see if I could get it to fail. Started it and during idle pulled the plug wire off each cylinder. There is definitely a larger RPM drop when the back cylinder is unplugged compared to the front cylinder. Thought it might be valve lash and adjusted that. Didn't fix it.

So, is this normal? If not, what do I check next?