At specified intervals, the air filter and PCV filter should be replaced with new ones, and a thorough program of preventative maintenance would call for periodic inspection of both filters between changes. The air filter is located inside the air cleaner housing on the top of the engine; to remove it, unscrew the wing nut at the top of the air cleaner and lift off the top plate, noting and disconnecting any vacuum hoses connected to this plate. While the top plate is off, care should be taken not to drop anything into the carburetor. The air filter can then be lifted out of the housing, and to check its condition, hold it up to strong sunlight or use a flashlight on the inside; if light passes through the paper element, the filter is acceptable, and it should be checked all around. The inside of the air cleaner should be wiped out with a rag, and the old filter (if in good condition) or the new filter (if the specified interval has elapsed) should be placed back into the air cleaner housing, ensuring it seats properly at the bottom. Any disconnected vacuum hoses should be reconnected to the top plate, which can then be reinstalled along with the wing nut, taking care not to over-tighten it. The PCV filter, mounted on the rocker arm cover, should be located, and the hose disconnected to remove the filter. The PCV filter assembly should be thoroughly washed in solvent, then wet by inverting it and pouring SAE 30-weight engine oil through the mounting nipple, allowing the oil to drain through the vent nipple on top of the filter before reinstalling the PCV filter and connecting the vent hose.