It is not safe to clean a carburetor with a pressure washer. Carburetors are often very delicate and are designed to be cleaned with chemical solvents. Using a pressure washer to clean your carburetor can damage internal components, push debris deeper into carburetor openings and even injure the user.
The safest way to clean a carburetor is to remove it completely from the engine it belongs to and carefully dissemble it on a work bench. Clean the disassembled carburetor with spray cleaner, or a chemical dip cleaner for especially dirty or varnished carburetors. Many modern carburetors for small engines are made from plastic so it is important to ensure that the cleaner you are using is safe to use on plastic products.