Seems to be a common problem? I changed my plugs to irridium when I pulled the old middle plug out it was sooty, so 200 miles on new plugs I took new plugs out to check condition, SOOTY, the outer plugs are perfect. Ballanced carbs,changed air filter, swapped coils eg. left to center etc. Still sooty center. PVL coils, Mikuni carbs, standard pipes, Bike starts easily runs great no misfires? Bike has done 9,500 miles. Before I start pulling carbs apart any ideas?