When the engine is working, the inhaled air first passes through the air filter, and impurities such as grit and dust in the air are adsorbed on the surface of the filter element, so as to avoid the wear of mechanical parts caused by entering the engine.

1. The filter paper porosity of poor air filter is usually too large, resulting in poor filtering effect. The sealing effect between the filter frame and the filter housing is not good, which leads to the air entering into the cylinder without filtering, which aggravates the wear between the cylinder and the piston and causes irreversible damage to the engine.

2. If the pore of air filter paper is too small, it will lead to the decrease of air intake of engine, thus affecting the power of engine, resulting in poor acceleration, increased fuel consumption and excessive exhaust gas.