Get rid of old Fuel residue ...

berryman's full stop.

but, you want berryman professional chem-dip carburetor and parts cleaner. the 5gal is PN 0905 and like $350, which is a great deal if you're doing a bunch of work. but not everybody needs that... so they sell it in 1gal "replenisher" size PN 0901 which is enough to dip small carbs. you will need a metal bucket (or bowl) and parts basket.

the berrymans 1gal that's available at vato-zone and the like is totally toothless (at least here in CA) and will work okay for carbs that aren't super bad.

a bucks down approach is, no ****, pine-sol. cut it 50/50 and soak over night, but be aware that some times there's a little discoloration of the metal.