Stihl MS660 Bogs In The Cut

Introduction

This tutorial provides a step-by-step guide on diagnosing and repairing a Stihl MS660 chainsaw that experiences low power and bogs down during operation. By following these instructions, you can effectively troubleshoot common issues related to fuel and carburetor performance, ensuring your chainsaw runs smoothly.

Step 1: Inspect the Fuel Tank

• Check the fuel tank for any signs of water contamination.
• If water is present, drain the fuel tank completely.
• Clean the tank to remove any residual contaminants.

Step 2: Examine the Cylinder Condition

• Remove the cylinder cover to inspect for scoring or damage.
• Ensure the cylinder is clean; any scoring may indicate a more serious issue.
• If the cylinder looks good, proceed to the next steps.

Step 3: Inspect the Spark Plug

• Check if the spark plug is new or recently replaced.
• Ensure the spark plug is not excessively dirty or fouled.
• If the spark plug is in good condition, reinstall it without replacing unless necessary.

Step 4: Check the Fuel System

• Examine the impulse line for cracks or disconnections.
• Test the fuel filter for blockages, as a plugged filter can cause lean running conditions.
• Conduct a pressure test on the fuel line to ensure it holds at least 10 pounds of pressure.

Step 5: Disassemble the Carburetor

• Remove the carburetor from the chainsaw.
• Inspect the carburetor for any blockages, particularly in the micro screen.
• Check the metering diaphragm for stiffness or wear.

Step 6: Clean and Rebuild the Carburetor

• If you find scum or debris, clean the carburetor thoroughly.
• Replace the micro screen and metering diaphragm with a new kit.
• Ensure the metering lever and needle valve are functioning correctly before reassembly.

Step 7: Reassemble the Carburetor

• Install the gaskets and follow this order: gasket first, then the diaphragm.
• Ensure the metering diaphragm’s notch aligns correctly with the metering lever.
• Reattach the throttle linkage and fuel line carefully to avoid damage.

Step 8: Perform a Function Check

• Before fully reassembling the chainsaw, do a function check to ensure everything operates smoothly.
• Ensure all components are properly connected and functioning.

Step 9: Test Run the Chainsaw

• Fill the carburetor with fuel and attempt to start the chainsaw.
• Note how many pulls it takes to start compared to before the repair.
• Observe the chainsaw's performance, ensuring it no longer bogs down.

Conclusion

By following these steps, you should be able to diagnose and repair the low power issues with the Stihl MS660 chainsaw. Regular maintenance, including checking the fuel quality and cleaning the carburetor, can prevent similar problems in the future. If issues persist after these repairs, consider consulting a professional for further assistance.