Seafoam works great for removing deposits on valves and carbon off pistons. We never pour it in the tank for that..Vacuum line is best but can be dumped down carb/Throttle body at idle feathering the throttle. Let it set for 20 minutes and watch the smoke show and hope no neighbors call the fire department FWIW a mixture of water and trans fluid will also do a really good job cleaning out carbon in the chamber.