See Figures 1 and 2
The air cleaner has a dual purpose. It not only filters the air going to the carburetor, but also acts as a flame arrester if the engine should backfire through the carburetor. If an engine maintenance procedure requires the temporary removal of the air cleaner, remove it; otherwise, never run the engine without it. Unfiltered air to the carburetor will eventually result in a dirty, inefficient carburetor and possible engine damage.
To replace the filter, simply remove the wingnut located on the top of the air cleaner assembly and remove the air cleaner lid. Replace the filter assembly and reinstall the lid. Inspect the air filter and housing assembly for excessive contaminants, such as leaves and oil. If an excessive amount of oil is present in or on the filter assembly, inspect the PCV system for proper operation or the engine for mechanical damage such as bad piston rings.