If you have been doing a lot of city driving in cold and damp conditions with the choke on to start and not really getting up to operating temperature that could be contributing to your sooty plugs. Take the bike out for a sustained run, ten miles over 4500, and get it nice and hot before pulling the plugs again and if possible pull in the clutch, drop it into neutral, and shut off the engine with no compression braking before pulling the plugs. That will give a more accurate indication of your carb set up.
I wouldn't change anything on your carbs until you have tested it with reset valves. Carbs are really tempting to adjust but aren't always the first place to start. And in this case, apparently running too rich is much better than running too hot and burning something up on your trip.
Steve