Get to your nearest Ace Hardware and buy some "Chore Boy" copper scouring pads. Unroll one of the pads a little (2" or so) cut it off and wrap it around a brass bore brush. Work that brush in the cylinder chambers, you should easily remove the fouling/carbon/lead residue. I have an old aluminum cleaning rod that I cut the handle off of, and I chuck it in an electric drill to clean the chambers. Run for about 20 sec on medium speed in each cylinder chamber and you should be good to go. I use Kroil as a lube, but CLP, or even motor oil will work.
Don't get discouraged, this technique is proven, safe, and it just plain works!
Lou