Don't bother. "Blowin out the carbon" by running at high speed does not work on a severely carboned up engine. Once the buildup is in place, running the engine faster/harder only makes more heat. You are better off ensuring you get a decent high temp/speed/load run in on a periodic basis to clean out the SMALL amount of buildup that accumulates in stop and go traffic in the course of a week.
Dribbling a carbon cleaner or plain old water in the carb while running at a fast idle (VERRY small amounts at one time) does a better job as the "shock" of the cold fluid and temporarily higher cylinder pressures loosen the carbon better.
Better yet is to get a head gasket and pull the head, scrape off the carbon with a spoon or related dull instrument (you don't want to scratch the piston) and reassemble. It is a good idea to put an old ring on top of the piston as you scrape so you don't remove the band of carbon around the periphery as it assists in the cylinder seal. Also the ring will help keep bits of carbon out of the rings where they could cause trouble upon start-up if they are packed in there.
Mike!