A scratching or scraping sound when starting your Yamaha bike could be indicative of a few potential issues. Here are a few possibilities to consider:
Starter Motor: The sound could be coming from the starter motor itself. If the starter motor is not engaging properly or if the gears within it are worn or damaged, it can produce a scratching or grinding noise. In such cases, it's advisable to have the starter motor inspected and repaired or replaced if necessary.
Clutch: If the sound occurs when you engage the clutch and start to release it, it could be due to a worn or damaged clutch component. A faulty clutch can cause a scratching noise during engagement. Consulting a mechanic to inspect and adjust or replace the clutch if needed would be recommended.
Chain or Sprockets: A loose or worn chain, or damaged sprockets, can also generate a scratching sound. Check the tension of the chain and ensure it is properly lubricated. If the chain is excessively loose or showing signs of wear, it may need to be adjusted or replaced. Damaged or worn sprockets should also be inspected and replaced if necessary.
Engine Components: In some cases, internal engine components, such as the piston rings or valves, could be causing the noise. If the noise persists even after ruling out issues with the starter motor, clutch, and chain, it would be advisable to have a qualified mechanic examine the engine for any potential problems.
Remember, diagnosing the exact cause of a noise without a physical inspection can be challenging. It is recommended to consult a professional Yamaha mechanic or technician who can perform a thorough examination and provide an accurate diagnosis based on the specific symptoms and the condition of your bike.