Take the carb off along with the back plate, save the seals. Remove the head if you so desire. Remove the muffler. Immerse all of it in a crock pot containing anti-freeze solution (undiluted, straight out of the container), slow cook the engine for 8 to 12 hours. Remove and wash off. Use a tooth brush or similar device and clean the outer surfaces of the engine. Make sure engine is dry, add liberal amounts of after run oil down the intake, inside the crankcase, on top of the piston, move all the parts around, reassemble what you took apart.

Your engine will be clean if not shinny bright again. Note do not remove piston or sleeve. Make sure all water/anti-freeze solution is out of the engine. Make sure you use liberal amounts of lubrication when putting it back together.

Good luck

Chip