Carb lurgy.

I’ve looked at some suggestions for cleaning up carbs in an ultrasonic machine but wondered what would get rid of this?
I’ve used water and washing up liquid and had a scrape but it’s getting into the nooks and, of course, crannies.

There are quite a few specialist companies that strip, clean, inspect and refurbish carbs, often easier than messing with it yourself, they have all the kit and the experience, and parts, I sent the carbs from my old BMW away as it never ran right from the day I bought it! previous owners abilities were not in line with his confidence, there was some internal damage and a hairline crack from heavy handed use
came back spotless with new parts, and the bike ran smoother after that