Hi Papster, the best way to decarbonise an engine is to inject water into the inlet manifold when the engine is hot. A household squirty bottle is ideal for this. Squirt the water in at a rate that just starts the RPMs to fall. You will need to do this once with the compression valves open and once with them closed, should clear the carbon.
There are proprietary products like Seafoam that will do the same thing.
Bob