Use fuel only, inside and out. With a stiff brush and some wrist grease, soak it, and brush, and soak, and brush, till you got all goo off.
The inside, just soak it until the engine is loose, gently apply rotation torque pressure until it budges. Do not force anything. Heating with a paint stripper helps solving the dried oil into the new fuel.
The carb fuel passages should be cleaned in fuel as well, unless you want to experience sudden flame-outs by undissolved flakes lodginging between needle and seat.

This is worst when the engine has been run on castor fuel. Wake her up right, and you will do well.

If all else fails, use the crock pot method, and simmer the engine for a while in anti-freeze fluid. Do not use your wifes cooking pot for this. AF is a sweet tasting poison you do not want to ingest.