Interesting no one has replied to this. If you are talking about carbon in the combustion chamber, you need to go through the fuel system. Lucas, Seafoam, and Chevron Techron are all good products for this. If you have sticky lifters or sludge in the engine, you could use sea faom or other aftermarket products, but old timers would tell you to save your money and add a quart of ATF, or diesel fuel, run 50 miles and change your oil and filter. Having said all this, if you don't have an issue with sticky lifters, and you didn't see any sludge when you pulled your valve covers, don't worry about doing any of the above. Useing quality fuel and keeping your oil changed is best.