Old Fart, the best method I know of to loosen and remove gunk on any engine is a good soak in hot glycol anti freeze. I found an old crock pot at a resale shop for $8 as it can never be used for food processing again. You also want to do this outside as the fumes can be toxic.
The good thing is the glycol does not harm rubber gaskets and seals and can be reused if filtered upon return to the container.
I believe the longest I've ever needed to boil parts was 2 hours. Even the baked on castor outside the muffler disappeared to give me an "OOOH Shiny!" appearance. Letting the bits cool, a rinse with cold water, blow dry, (including any lube, fuel and vent passages) and a good dose of oil for all the rotating/sliding parts should be all that's required. You may want to remove the rear and valve covers to allow penetration.