After a few rides or when the air filter looks dirty you need to clean it. Some riders use the old-school method of gasoline but better options exists keeping you from the fumes and overall toxic power of gas. Most air filter oil companies also make air filter oil cleaner. The cleaners quickly dissolve the old air filter oil and wash away the dirt. Once thoroughly dry, reapply new air filter oil. Maxima makes a great oil filter cleaner, PJ1 has a popular foam air filter cleaner and No Toil makes a biodegradable air filter cleaner.