I've seen it suggested that in lieu of an ultrasonic cleaner you can simmer your parts in a pot on the stove top.
You don't want it boiling just simmering.
You'll want to remove any plastic and rubber o rings. Just put metal components in.
You'll want to use a gentle cleaner like dish washing liquid or something that won't eat the aluminium.
You'll probably want to do it outside if you can and you'll probably also want to avoid using the pot again for food.
Having said that I also don't have an ultrasonic cleaner so I normally just disassemble the carb fully (remove emulsion tubes and jets etc) and give it a going over with carb or brake cleaner and give it a scrub with a brass wire brush for the external parts and use a spray gun cleaning kit for the jets and tube and internal passages.
If it's really gummy (like a thick gel) I find acetone makes short work of it.
If that fails, I usually just replace the carb.
