FWIW I offer the following tip: Go to your Mercury Marine dealer and buy a spray can of Mercury Power Tune Engine Cleaner. Remove the cylinder and place it upright on the bench on a few layers of paper towels and spray in each chamber. It will foam up. Let it sit for while and then brush and run clean patches through each chamber. Repeat if necessary.
Power Tune is formulated to remove carbon fouling from outboard combustion chambers. Even if you think you have cleaned the carbon from your cylinder you may be surprised at the black residue removed by this process. It can also remove carbon fouling forward of the chamber in high performance centerfire rifles.
