The air filters differ from one model of a lawnmower to the other and it is a rule of thumb that they shield the engine from both debris and dust. While some can be cleaned, others will have to be replaced especially if they are paper air filters. The lawnmower should not be on during cleaning. The cord of the spark plug should also be off since it can be a source of accidents during cleaning. The next step involves removing the housing of the air filter. Place the air filter in hot, soapy water to get rid of any dirt or debris during this time and once it is clean, rinse it and ensure the water is drained well. You can use some motor oil on the air filter. Put it back to its original place and cover it firmly.