What device typically experiences issues resulting in an engine running rich under certain conditions?

The carburetor plays a crucial role in the proper functioning of an engine's air-fuel mixture. When a carburetor experiences issues, one common symptom is an engine running rich, which means it receives more fuel than necessary for effective combustion. This condition can occur due to various factors like a clogged jet, a stuck float, or incorrect adjustments.

When the carburetor is not allowing enough air into the mixture or is providing too much fuel, the engine may not burn the fuel completely, which can lead to poor performance, increased emissions, and fouled spark plugs. Adjustments or repairs to the carburetor can help restore the correct air-fuel balance, ensuring that the engine runs efficiently and cleanly.

Other systems, such as the ignition or exhaust systems, do not directly control the fuel-to-air ratio, making them less likely to cause an engine to run rich. The cooling system, while essential for preventing overheating, does not influence fuel mixture, further distinguishing the carburetor as the primary device responsible for rich running conditions.