In a four-stroke engine, which part is NOT included in emission control?

In a four-stroke engine, the oil filter is not part of the emission control system. Emission control systems are specifically designed to minimize the pollutants released into the atmosphere as a result of the combustion process. The exhaust system plays a crucial role in this, as it directs exhaust gases out of the engine and often incorporates components like catalytic converters that further reduce harmful emissions.

The carburetor is also significant because it is responsible for mixing air and fuel in the correct proportions for efficient combustion, which directly impacts emissions. Furthermore, the fuel tank, while not a direct part of the emission control system, is still involved since the fuel itself can impact emissions based on its composition and quality.

In contrast, the oil filter's primary purpose is to remove contaminants from the engine oil to ensure proper lubrication and functioning of the engine components. It does not have a direct function related to controlling or reducing emissions from the engine’s exhaust, making it clear why it is excluded from emission control considerations.