When experiencing a clicking noise from the top end of your motorcycle's engine and experiencing bogging out when revving, there are a few areas you can inspect for potential issues. Here are some possible causes to consider:
Valve Train: A clicking noise from the top end could indicate a problem with the valve train. Inspect the valves, valve clearances, and camshafts for any signs of damage, wear, or misalignment. Incorrect valve clearances can cause noise and affect engine performance.
Cam Chain or Timing Chain: The clicking noise could be due to a loose or worn cam chain or timing chain. Check the tension of the chain and ensure it is properly adjusted. A loose chain can cause irregular valve timing and affect engine performance.
Piston and Cylinder: Inspect the piston and cylinder for signs of damage, scoring, or excessive wear. A worn piston or cylinder can lead to poor compression, reduced power, and abnormal noises. Ensure the piston rings are in good condition and sealing properly.
Spark Plugs: Check the spark plugs for fouling, wear, or incorrect gap. Faulty or worn spark plugs can cause misfiring, poor combustion, and affect engine performance.
Fuel System: A bogging out issue when revving can be related to the fuel system. Inspect the fuel filter, carburetor (or fuel injectors), and fuel lines for clogs, blockages, or fuel delivery problems. Ensure the carburetor jets are clean and properly adjusted. If your motorcycle has fuel injection, consider checking the fuel pressure and injector operation.
Air Intake: Check the air filter for clogging or dirt accumulation. A dirty or clogged air filter can restrict airflow and affect engine performance.
Ignition System: Inspect the ignition system components such as the ignition coil, spark plug wires, and CDI (capacitor discharge ignition) unit if applicable. Faulty ignition components can cause misfiring, weak sparks, and affect engine performance.
If you are unsure about performing these inspections yourself or if the issues persist after inspection, it's recommended to consult a qualified motorcycle mechanic or technician who can diagnose the problem accurately and provide appropriate repairs.