We recommend the following procedure - Take out the spark plugs and pour 1/4 can of Berryman B-12 Chemtool Fuel Injector Cleaner (Part #0116) into each cylinder.  Thread the plugs back in finger-tight and let them soak for at least an hour, longer if it's much below 65°F (overnight would be fine).  Don't worry about leak-down.  When you're ready to remove the cleaner/carbon mixture, it's ideal if you can blow a little air into the liquid immediately before suctioning the mixture back out.  This will help suspend any loosened carbon.  If there is leakage of the 0116 into the crankcase, that is not a problem.