Originally Posted by kenwelch
The engine piston rings prevent the loosened contaminates from mixing with the engine oil. Their purpose is to seal the combustion chamber from the crankcase. When you remove fuel injector contaminates using fuel system cleaners they are sometimes pushed out with the exhaust and some might become additional contaminates on the spark plugs. Because you are using fuel system cleaner added to the gasoline it works to help clean fuel injectors not the spark plugs. The mix ratio of cleaner to fuel reduces the cleaning action compared to EFI cleaning machines and direct application combustion chamber cleaners.
When using fuel injection cleaning machines and strong combustion chamber cleaners it is sometimes worth changing the spark plugs after completing the cleaning process.
Your right. The only way for any carbon that is loosened up to be expelled would be through the exhaust valves. thanks for the clarification, I've should have known this...