The only way that I have found to work is an antifreeze bath. I have tried several of the expensive cleaners in the can with the brush in the lid and they were a total waste of money and time.
Do a search and you will find many explanations of the anti-freeze/crockpot method. It works and you can leave the engine assembled if you want. I would take the carb off just to keep foreign particles from getting into places they shouldn't.
Fred