I have used carb cleaner or brake cleaner in the past and compressed air from a can, but that's about it. Oh, and once some Yamaha carb cleaner, which was so toxic that the dealer who had given it to me, had it stored in a cupboard outside the workfloor of his workshop. It was also used in workshops to service outboard engines which often are inactive for most of the year. Later another mec commented that that stuff should never have been handed to me, a customer, and that this had been in violation with Yamaha's instructions to dealers. Hence my warning. Thinner is also nasty stuff and not to be used inside.
The oldstyle CB500/550 carbs are so simple - all the brassware is easily removed - that IMO you can do it all mechanically (if that's the right word or... is it manually?). I remember that in the past, I've made inquiries by phone at workshops which offered ultrasonic cleaning. All three were honest enough to stress they could not guarantee success... so I never bothered. After all, I didn't need it and was just curious. But maybe other more complex carbs with acceleration jets and stuff will benefit. At one occasion I discovered not all holes in the needle jets were open. I cleaned them ofcourse, but I have not been able to witness any difference in driveability thereafter. What I do know, is that fuel system cleaners can help. I guess owners of the CB550K3/4 with the newer PD carbs may benefit from a maintenance dose at every tankfill to keep the pilot jets cleared.
I wish I had the link to that thread where someone had his oldstyle CB500 carbs ultrasonically cleaned and afterwards discovered he had a hole in the #1 carb body; something small (a sort of a guide) was missing, possibly dissolved in the aggressive fluid used.
