What can I use to clean the inside of the carburetor?

Carburetor Cleaner in a spray can is made by a number of different manufacturers. You can find it at Walmart, any hardware store, or any auto parts store.

Personally, I prefer to use Brake Parts Cleaner, also in a spray can, for this purpose. Carburetor Cleaner is designed to vaporize rapidly so it burns in the engine. For rebuilding and cleaning disassembled parts, it doesn't give you much time to work with it. Brake Parts Cleaner is pretty much the same thing, but it is designed to not evaporate so quickly, giving you plenty of time to wash and rinse parts.

Here's a link to an article on the subject:

https://www.2carpros.com/articles/throttle-actuator-service

This is for a throttle body on a fuel-injected engine, but you might find some useful information.