Why does my Chevy 350 smoke black then smooths out?

1. Engine is running rich. This is the most common cause of black smoke from a Chevy 350 engine. When the engine is running rich, it is burning more fuel than it can properly process. This causes the fuel to build up in the cylinders and eventually burn off, creating black smoke.

2. Choke is stuck. The choke is a device that controls the flow of air into the engine. If the choke is stuck, it can cause the engine to run rich, resulting in black smoke.

3. Faulty oxygen sensor. The oxygen sensor measures the amount of oxygen in the exhaust gas. If the oxygen sensor is faulty, it can send an incorrect signal to the engine control unit (ECU), which can cause the engine to run rich.

4. Faulty fuel injector. A faulty fuel injector can cause the engine to run rich by spraying too much fuel into the cylinders.

5. Worn piston rings. Worn piston rings can allow oil to leak into the combustion chambers, which can cause the engine to run rich and produce black smoke.