It's an old trick, and not really very effective. I'd reccomend a slightly different technique, though. Run the idle speed up to around 1,500 RPM or a little more, with the engine at normal operating temperature. Use a spritz bottle like for Windex, or something similar, and spray the water into the carb inlet. The water flashes to steam as it hits the hot combustion chamber, and supposedly blows the carbon deposits away. It might not help, but it probably won't hurt, unless you get a big slug of liquid into a cylinder and bend a connecting rod.
Jerry
