Rode home the other night and while leaving my bike idling while I opened the garage door I could hear it missing on one cylinder and stalled in a moment. Fired back up, but the next day while riding, high speed seemed OK but as I throttled down ,it started missing. Pulled the plugs and they looked ok , gap good. Cleaned them , back together and same result. I thought a coil issue but if I pull the choke out it will smooth out and run better. Before I start tearing everything apart guessing at it I thought I'd look for advice.
Since it runs fine with the choke pulled out, it sounds more like a fuel issue, more specifically a venting issue. You might try opening the gas cap, see if that helps. I could be wrong, but it sounds pretty close to a couple of the issues that I ran into when I was figuring out the tank vents on my bike (getting rid of the charcoal cannister and stuff). And it's really easy to check.
Vacuum leak? The hoses and stuff are now quite old, and nothing lasts for ever....If Having a little enrichment fixes it, then look for a cracked hose.