Since leaded gasoline went away, I haven't seen the need to de-carbon ANY engine that was in good mechanical condition.
Chevrolet used to recommend heavy misting water into the carburetor in the mid '60's to clean carbon off piston tops. I've done it on large and small engines both.
If the engine needed it, you'll see small pieces of carbon fly out of the muffler. The carbon gets blown out of the combustion chamber by the steam the water creates.
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