🔍 Key Concepts

• diesel engine combustion and air-fuel mixture • effects of restricted air flow vs. restricted fuel flow • color of exhaust smoke and what it indicates about combustion

💭 Think About

• Think about what black smoke usually means about how completely the fuel is burning inside the cylinders. • Ask yourself: which option would make the mixture too "rich" (too much fuel for the air available) and lead to incomplete combustion? • Consider which listed problems would reduce the amount of air getting into the engine, and which would reduce fuel.

✅ Before You Answer

• Black smoke typically indicates unburned or partially burned fuel in the exhaust. • Identify which choice would most likely reduce the air supply to the cylinders, not the fuel supply. • Eliminate any option that would improve scavenging or air flow, since that would usually reduce, not increase, black smoke.