The gasoline enters the carburetor from the fuel tank through the gasoline filter, which can filter out the impurities mixed in the gasoline and the oxide skin in the fuel tank. If the quality of the filter is defective, some impurities still enter the carburetor through the filter. In addition, gasoline contains components that can form colloids. After long-term deposition, colloids will condense and adhere to the parts of the carburetor (such as measuring holes), oil passages and the surface of the float chamber.
The air enters the carburetor through the air filter. Based on the consideration that the intake resistance cannot be too large and other factors, the filter device cannot be too dense, so some tiny impurities in the air will still enter the carburetor through the air filter. If the filter quality is defective, it will cause more serious effects.