If your Pulsar RS 200 is emitting black smoke when revved hard, it could indicate an issue with the fuel-air mixture. Here are a few possible causes to consider:
Rich fuel mixture: Black smoke typically indicates that the engine is running rich, meaning there is an excessive amount of fuel in proportion to the air. This can be caused by a malfunctioning fuel injection system, a clogged or leaking fuel injector, or a faulty fuel pressure regulator. It's recommended to have the fuel system inspected and potentially cleaned or repaired by a qualified mechanic.
Air intake restriction: A restricted air intake can disturb the proper fuel-air mixture, leading to black smoke. Ensure that the air filter is clean and not clogged. If the air filter is dirty, it may need to be replaced. Additionally, check for any obstructions in the intake system, such as blocked air passages or a malfunctioning throttle body.
Ignition system issues: Although you mentioned changing the spark plugs, it's still worth verifying that they are correctly installed and properly gapped. Faulty spark plugs or a malfunctioning ignition system can lead to incomplete combustion, resulting in black smoke. Consider having the ignition system inspected and tested by a mechanic.
Engine sensors: Malfunctioning engine sensors, such as the oxygen sensor or the mass airflow sensor, can provide incorrect readings to the engine control unit (ECU), leading to an imbalanced fuel-air mixture. A diagnostic scan of the ECU can help identify any sensor-related issues.
Given the complexity of diagnosing and resolving engine problems, it's advisable to seek assistance from a certified mechanic or take your bike to an authorized service center. They will have the necessary expertise and diagnostic tools to identify the root cause of the black smoke and perform the required repairs or adjustments.