Heres something I did when I was working on one of the sets of carbs for one of my Mk1 Bandit 1200s. As I had them apart and the bodies emptied, I decided to throw them in the lathe and clean up the bellmouths. I didn't want anything highly mirror polished, I was mainly concentrating on getting the casted surface a bit smoother.
Once each carb update was completed, they then went in the ultrasonic cleaner to clean them up before reassembly.
Here you see the updated bellmouth on the left versus a stock one on the right. Quite a difference.