I recently went to an auction and bought several boxes of old carbs, probably at least 30 of them in fact. My plan was to work on them in my free time this winter and then sell them next year. I've generally started each carb with a soak in one of those commercially available gallon of carb cleaner, then disassemble, then clean in an ultrasonic and blast cabinet where necessary, but with this many carbs to do I was hoping to find a cheaper alternative to the $40 gallons, for at least the initial clean up. 

The carb soak stuff you find in one-gallon cans is a cocktail of some rather nasty components... hence the price, and effectiveness.

Most if it makes excellent work of cast iron carb parts, and has no problem clearing shellac from brass, stainless, etc.,  but it can be pretty harsh on Zamak.  Most antique tractor carbs (Marvel-Schebler, Zenith, etc) will be iron bodies with brass orfices.  Newer stuff will be Zamak, or some flavor of aluminish die-casting stock.

I've been doing most of my carbs with the dip-can, followed by ultrasonic and bead-blaster.  I usually blast the exterior of mine BEFORE disassembly, THEN rinse it in degreaser, so the the exterior crud doesn't take away all the effectiveness of my dip-can.  It DOES mean that my blast cabinet gets cruddy, but it's gotta go Somewhere, right?

One trick I DO use... is distilled water and plastic baggies.  I'll fill the ultrasonic tank about 3/4 the way with distilled water, then put my carb parts in a plastic baggie, then pour some vinegar into the bag, zip it shut, and lower it into the ultrasonic.  That keeps the US tank clean, but the heat and ultrasonic energy passes through to the parts... with the heat, and the vinegar's acetic acid,  parts clean up pretty well.

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I'm a recent convert to Ultrasonic cleaner (HF small one).

Almost taking carbs off running tractors just to clean em up inside.

Dawn dishsoap is about the best initial cleaner you can use. Simple Green or Purple Cleaner or Orange cleaner added to the dawn does quite a lot in the UC.

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 Quite a while back, Dick L suggested boiling the carburetor.  I tried it and it cleaned up whatever orifice that was giving me problems. I still boil them and have pretty good luck.

I've heard a lot about the ultrasonic cleaners. Could someone explain how they work?

they create a sonic wave at 34,000-45,000 hz

those waves create a "bubble" that is actually a vacuum, and as it collapses, it creates a mini shock wave, literally knocking off anything that can be knocked off

it is so powerful, that it'll eat holes in aluminum foil.   I have heard of it pitting soft alloys of aluminum as well, but have never seen it

Home made US cleaner, take a plastic tub, a piece of 1/2" plywood, and a square faced, 1/4 sheet, random orbital sander, a tube of silicone sealer and 4 SS bolts/nuts/washers that fit the holes in the sander's face plate  

remove the rubber face on the sander

drill 4 holes through the plywood/tub the same as the holes in the sander's face plate.

cover one side of the plywood and matching tub area with silicone. also smear the bolts/holes.

mount the plywood on the inside, sander on the outside, sandwiching the tub material between, and bolt them up tight.

now, when you fill with water over the plywood, the sander's vibrations are transferred into the water and will knock loose a LOT of crud from stuff in the water.

works great on stuff that's covered in old grease/dirt etc

might work on carbs if using a detergent/solvent.