RE: carbon buildup and cleaning
I could not believe my eyes the first time I saw this, but I've since seen it work very effectively multiple times without adverse effects. An old timer showed me this. Crank up the engine and let it smooth out a little. Expose the carb and manually open her up to 3000-3500 and slowly pour about a quart of cool water into the carb- while it's running- and it will waste a goodly amount of the carbon gunking up the works. It'll sound like it's under water when you do this. I agree with others that carbon is likely not causing your smoking, but it certainly can reduce your airflow. I've not seen a negative result yet.