We often get inquires about how to loosen up frozen parts.
Keep in mind that when you have this problem you may be better off finding a better carburetor candidate. Frozen parts are often pitted, or rusted to a degree that makes them useless.
Most parts can be broken loose using heat. Apply heat using a propane torch to the outside of the part, while gently trying to move the part back & forth.
Parts that are frozen should be taken completely apart and buffed out to remove any rust. You of course chance breaking a part you can't get, so it's sometimes better to leave it alone.