I think your going in the right direction with a little warmer plug with a projected tip. the dry carbon is a rich condition. when you install the vacuum advance it will help clean-up the cruise a/f mix some. what carb/manifold and jetting are you using? you might take a magic marker and draw a line on the length of the plug where the clean spot on the rim of the plug is. try to see if that line lines up with the intake valve location.