6 Most Common Stihl MS 661 Problems: In-Depth Troubleshooting Solutions

Welcome to our comprehensive guide on the Stihl MS 661 chainsaw, a powerful tool for arborists, loggers, and outdoor enthusiasts. In this blog post, we will delve into the Stihl MS 661, highlighting its capabilities and exploring the most common problems users may encounter. We’ll also provide you with practical troubleshooting solutions, ensuring that your Stihl MS 661 remains in top working condition.

Brief Overview of the Stihl MS 661 Chainsaw

The Stihl MS 661 is renowned for its robust performance and reliability, making it a popular choice for professionals and homeowners alike. With a high power output, ergonomic design, and advanced features, this chainsaw is designed to tackle even the most demanding cutting tasks with ease. Whether you’re cutting firewood, felling trees, or maintaining a property, the Stihl MS 661 is a trusted companion.

Importance of Identifying and Resolving Common Problems

Like any mechanical equipment, the Stihl MS 661 chainsaw may encounter issues over time due to wear and tear or improper maintenance. These issues can affect its performance, safety, and longevity. Recognizing and addressing common problems is crucial for the following reasons:

  • Safety: Ensuring that your chainsaw operates as intended is paramount for your safety and the safety of those around you.
  • Cost-Efficiency: Timely troubleshooting can prevent costly repairs or replacements, saving you money in the long run.
  • Performance: A well-maintained Stihl MS 661 will deliver consistent and efficient cutting performance, which is especially important for professional users.

Purpose of the Blog Post

The purpose of this blog post is to equip Stihl MS 661 users with the knowledge and tools they need to tackle the six most common problems that can arise when using this chainsaw. By addressing these issues promptly, you can extend the life of your equipment and continue to enjoy its impressive cutting capabilities.

In the following sections, we will take an in-depth look at each of these common problems, providing step-by-step troubleshooting solutions and offering valuable maintenance tips.

Problem 1: Starting Issues

Starting issues can be frustrating when you’re eager to get to work with your Stihl MS 661 chainsaw. If your chainsaw won’t start or has difficulty starting, it’s essential to identify the root causes and apply the appropriate troubleshooting steps. Here, we’ll explore the possible causes, offer troubleshooting solutions, and provide tips for preventing starting problems in the future.

Possible Causes

  1. Fuel Problems: The most common reason for starting issues is improper fuel mixture or stale fuel. If the fuel isn’t mixed correctly, it can affect the engine’s ability to ignite.
  2. Air Filter: A clogged or dirty air filter restricts the flow of air to the engine, making it difficult to start.
  3. Spark Plug Issues: A fouled or worn-out spark plug may not generate the spark needed for ignition.
  4. Compression Issues: Low compression can prevent the engine from starting. This could be due to worn-out piston rings, cylinder scoring, or other internal problems.
  5. Ignition Problems: Faulty ignition components, like the ignition coil or module, can hinder the starting process.
  6. Carburetor Problems: A malfunctioning carburetor can disrupt the air-fuel mixture, making it difficult to start the engine.

Troubleshooting Steps

Step 1: Check the Fuel Mixture

Ensure that you’ve mixed the fuel according to the manufacturer’s specifications (usually a 50:1 ratio of gasoline to oil). If the fuel is stale, drain the tank and replace it with fresh, correctly mixed fuel.

Step 2: Inspect the Air Filter

Remove and inspect the air filter. If it’s dirty or clogged, clean or replace it. A clean air filter ensures proper airflow to the engine.

Step 3: Examine the Spark Plug

Inspect the spark plug for signs of fouling or wear. If necessary, replace it with the recommended spark plug for your Stihl MS 661.

Step 4: Check Compression

Low compression may require professional assistance. If you suspect compression issues, consult a Stihl service center for a thorough inspection and repair.

Step 5: Examine Ignition Components

Inspect the ignition coil, module, and wiring for any visible damage. If you notice any issues, it’s advisable to seek professional help for replacement or repair.

Step 6: Carburetor Inspection

If you suspect carburetor issues, it’s best left to professionals. A qualified technician can assess the carburetor and make the necessary adjustments or repairs.

Tips for Preventing Starting Problems

  1. Use Fresh Fuel: Always use fresh, high-quality fuel with the correct oil-gasoline ratio. Store fuel in an airtight container to prevent it from going stale.
  2. Regular Air Filter Maintenance: Clean or replace the air filter at regular intervals to ensure a consistent flow of clean air to the engine.
  3. Scheduled Spark Plug Replacement: Replace the spark plug according to the manufacturer’s recommendations, typically every 100 operating hours.
  4. Routine Maintenance: Follow the manufacturer’s maintenance schedule for your Stihl MS 661. Regular servicing by professionals can prevent many starting issues.

By following these troubleshooting steps and adopting preventive measures, you can ensure that starting issues don’t hinder your Stihl MS 661’s performance.

Problem 2: Poor Performance

Experiencing poor performance with your Stihl MS 661 chainsaw can be frustrating, especially when you rely on its cutting power for various tasks. In this section, we will dive into the symptoms of poor performance, and potential underlying issues, and provide you with effective troubleshooting and maintenance tips to restore your chainsaw’s performance to its peak.

Symptoms of Poor Performance

  1. Reduced Cutting Power: The chainsaw struggles to cut through wood efficiently and takes longer than usual to complete tasks.
  2. Overheating: Your Stihl MS 661 overheats more frequently during operation, which can lead to engine damage if left unaddressed.
  3. Increased Fuel Consumption: Poor performance can cause your chainsaw to guzzle fuel more quickly, leading to more frequent refueling.
  4. Inconsistent Idling: The chainsaw may have difficulty idling smoothly, which can make it challenging to work with precision.

Potential Underlying Issues

  1. Dull Chain: A dull chain is a common reason for reduced cutting power. Regularly sharpen your chain to maintain optimal cutting efficiency.
  2. Air Filter and Carburetor Issues: A clogged air filter or carburetor problems can affect the air-fuel mixture, leading to poor performance.
  3. Exhaust System Problems: A blocked or damaged exhaust system can cause overheating and reduced power output.
  4. Cylinder Scoring: Internal engine issues, like cylinder scoring or piston damage, can lead to poor performance. This may require professional inspection and repair.

Troubleshooting and Maintenance Tips

Step 1: Chain Maintenance

Regularly check the condition of your chain. Sharpen it when it’s dull, and ensure proper tension. A sharp chain is essential for efficient cutting.

Step 2: Air Filter and Carburetor Inspection

Clean or replace the air filter if it’s dirty or clogged. Additionally, check the carburetor for any issues. Cleaning or adjusting it may be necessary to ensure the right air-fuel mixture.

Step 3: Exhaust System Check

Inspect the exhaust system for blockages, damage, or carbon buildup. A clean and unobstructed exhaust system helps maintain optimal engine temperature.

Step 4: Compression and Engine Inspection

If poor performance persists, have a professional technician check the engine’s compression and internal components. They can identify and repair any internal damage affecting performance.

Step 5: Regular Maintenance

Following the manufacturer’s recommended maintenance schedule is crucial for preventing poor performance. Regular servicing can catch potential issues before they affect your chainsaw’s performance.

Step 6: Proper Fuel and Oil

Ensure you’re using the correct fuel mixture and high-quality chain oil. Subpar fuel or oil can lead to poor engine performance.

By following these troubleshooting and maintenance tips, you can address poor performance issues with your Stihl MS 661 chainsaw effectively.

Problem 3: Chain Slippage

Chain slippage can be a frustrating issue when using your Stihl MS 661 chainsaw. It not only hampers productivity but also poses safety risks. In this section, we will explore the causes of chain slippage, how to diagnose and fix the issue and provide valuable chain tension and maintenance guidelines.

Causes of Chain Slippage

  1. Improper Chain Tension: One of the most common reasons for chain slippage is incorrect chain tension. If the chain is too loose, it can come off the bar during operation.
  2. Worn Bar or Sprocket: Over time, the chainsaw bar or sprocket can wear out, leading to poor engagement with the chain and causing it to slip.
  3. Damaged Drive Links: A damaged or worn-out drive link can also cause chain slippage as it struggles to grip the bar and sprocket.
  4. Lubrication Issues: Inadequate lubrication to the chain and bar can increase friction, making it more likely for the chain to slip.
  5. Debris Buildup: Accumulated sawdust or debris in the chain and bar area can interfere with proper chain movement and tension.

How to Diagnose and Fix the Issue

Step 1: Safety First

Before diagnosing and fixing chain slippage, ensure the chainsaw is turned off and that you’re wearing appropriate safety gear, including gloves and eye protection.

Step 2: Check Chain Tension

Inspect the chain tension. If it’s too loose, tighten it according to the manufacturer’s recommendations. Make sure the chain can be pulled by hand with some resistance but can still move freely.

Step 3: Examine the Bar and Sprocket

Inspect the chainsaw bar and sprocket for signs of wear, damage, or excessive grooving. If either component is compromised, consider replacing them.

Step 4: Inspect Drive Links

Examine the drive links on the chain for any visible damage or wear. If any drive links are damaged, replace the chain.

Step 5: Lubrication Check

Ensure that the chain and bar receive proper lubrication during operation. Lack of lubrication can increase friction and contribute to chain slippage. Adjust the lubrication system as needed.

Step 6: Clean the Chain Area

Regularly clean the chain area to remove sawdust and debris. Cleanliness ensures smooth chain movement and proper engagement.

Chain Tension and Maintenance Guidelines

  • Regular Checks: Check the chain tension before each use and make adjustments as needed. This will prevent the chain from becoming too loose during operation.
  • Proper Lubrication: Ensure the chain and bar receive an adequate amount of chain oil to reduce friction and heat buildup. A well-lubricated chain is less likely to slip.
  • Replace Worn Components: If you notice signs of wear or damage to the bar, sprocket, or chain, replace them promptly to maintain safe and efficient operation.
  • Frequent Cleaning: Regularly clean the chain and bar area to prevent debris buildup, which can affect chain tension and performance.
  • Professional Maintenance: Periodically schedule professional maintenance to keep your Stihl MS 661 in top condition. This includes inspecting and adjusting the chain, bar, and other components.

By following these guidelines and taking prompt action to diagnose and fix chain slippage, you can ensure that your Stihl MS 661 chainsaw remains safe and productive.

Problem 4: Overheating

Overheating can be a serious issue when operating your Stihl MS 661 chainsaw. It not only affects the chainsaw’s performance but can also lead to engine damage if not addressed promptly. In this section, we’ll explore the signs of an overheating chainsaw, how to identify the causes and provide effective solutions and preventive measures.

Signs of an Overheating Chainsaw

  1. Excessive Heat: The chainsaw feels excessively hot to the touch during operation.
  2. Reduced Performance: Overheating often leads to a decrease in cutting power and efficiency.
  3. Stalling or Shutdown: The chainsaw may stall or shut down unexpectedly due to overheating.
  4. Smoke or Unusual Odors: You may notice smoke or unusual burning odors coming from the chainsaw, which are clear signs of overheating.

Identifying Overheating Causes

  1. Lubrication Issues: Inadequate chain and bar lubrication can increase friction, generating excess heat. Check the lubrication system and adjust it as needed.
  2. Dirty Air Filter: A clogged air filter restricts airflow, causing the engine to run lean, which can lead to overheating.
  3. Incorrect Carburetor Adjustment: A carburetor set too lean can result in higher temperatures. Ensure the carburetor is adjusted according to the manufacturer’s specifications.
  4. Worn or Damaged Components: Worn-out or damaged parts, such as the chain, bar, or sprocket, can create friction and heat. Inspect these components for wear.
  5. Continuous High RPM Operation: Prolonged operation at high RPM levels without letting the chainsaw cool down can contribute to overheating.

Solutions and Preventive Measures

Step 1: Immediate Shutdown

If you suspect your Stihl MS 661 is overheating, shut it down immediately. Allow it to cool before attempting any troubleshooting.

Step 2: Lubrication Check

Ensure the chain and bar receive proper lubrication during operation. Adjust the lubrication system to provide adequate oil to reduce friction and heat buildup.

Step 3: Clean the Air Filter

Regularly clean or replace the air filter to maintain proper airflow to the engine. A clean filter prevents the engine from running too lean.

Step 4: Carburetor Adjustment

If you’re experienced with chainsaw maintenance, you can check the carburetor adjustment. However, it’s recommended to consult a professional to ensure it’s set correctly.

Step 5: Inspect Components

Examine the chain, bar, and sprocket for wear and damage. Replace any worn or damaged components to prevent overheating.

Step 6: Avoid Continuous High RPM Operation

To prevent overheating in the first place, avoid operating your chainsaw at high RPM levels for extended periods. Give it time to cool down between heavy use.

Step 7: Regular Maintenance

Follow the manufacturer’s recommended maintenance schedule. This includes routine checks and adjustments by professionals to keep your Stihl MS 661 in excellent working condition.

By following these solutions and preventive measures, you can effectively address overheating issues and ensure the longevity and performance of your Stihl MS 661 chainsaw. In the next section, we’ll tackle “Problem 5: Oil or Fuel Leaks” and provide guidance on how to resolve these common issues.

Problem 5: Oil or Fuel Leaks

Oil or fuel leaks in your Stihl MS 661 chainsaw can be messy and potentially hazardous if not addressed promptly. In this section, we’ll explore the types of leaks, and the root causes behind them, and provide comprehensive steps to fix and prevent oil and fuel leaks.

Types of Leaks

  1. Oil Leaks: Oil leaks are characterized by the presence of chain oil on the chainsaw, bar, or ground while operating or when the chainsaw is stored. This can result from various issues within the oiling system.
  2. Fuel Leaks: Fuel leaks involve the escape of gasoline from the chainsaw. You may notice a strong smell of fuel or actual fuel on the chainsaw or ground, which can pose a safety risk.

Root Causes of Leaks

Oil Leaks:

  • Oil Tank Issues: Cracks or damage to the oil tank can lead to oil leaks.
  • Oil Line Blockage: A clogged oil line can disrupt the flow of chain oil.
  • Faulty Oil Pump: A malfunctioning oil pump can lead to inconsistent oil delivery.

Fuel Leaks:

  • Damaged Fuel Lines: Cracks or damage to the fuel lines can cause fuel leaks.
  • Loose or Damaged Fuel Cap: A loose or damaged fuel cap may not seal properly, allowing fuel to escape.
  • Carburetor Problems: Issues with the carburetor can result in improper fuel management and leakage.

Steps to Fix and Prevent Oil and Fuel Leaks

Step 1: Safety First

Before addressing any leaks, ensure the chainsaw is turned off, and you’re wearing appropriate safety gear, including gloves and eye protection.

For Oil Leaks:

Step 2: Check the Oil Tank and Cap

Inspect the oil tank for cracks or damage. Ensure that the oil cap is tightly sealed and not cracked.

Step 3: Clear Oil Line Blockages

Check the oil lines for any clogs or blockages. Clear any obstructions that are impeding the flow of chain oil.

Step 4: Examine the Oil Pump

Inspect the oil pump for proper functioning. If it’s malfunctioning, consider seeking professional assistance for repairs or replacement.

For Fuel Leaks:

Step 2: Inspect Fuel Lines and Cap

Examine the fuel lines for cracks or damage. Ensure the fuel cap is tightly sealed and not compromised.

Step 3: Carburetor Inspection

If you suspect carburetor issues, consider seeking professional help for inspection and adjustment.

Step 4: Replace Damaged Components

If you identify any damaged components, such as fuel lines or caps, replace them promptly to prevent further leaks.

Step 5: Preventive Maintenance

To prevent future leaks, follow the manufacturer’s maintenance schedule, and conduct routine checks on fuel and oil systems.

Step 6: Correct Storage

When storing your chainsaw, store it in an upright position with the cap closed to prevent leaks.

By following these steps and conducting regular checks and maintenance, you can effectively address and prevent oil and fuel leaks in your Stihl MS 661 chainsaw, ensuring a clean and safe operation.

Problem 6: Chain Brake Failure

A functioning chain brake is not just a convenience but a critical safety feature in your Stihl MS 661 chainsaw. Chain brake failure can lead to serious accidents and injuries. In this section, we’ll emphasize the importance of a functioning chain brake, provide guidance on diagnosing and addressing chain brake problems, and offer maintenance practices to ensure your chain brake remains reliable.

The Importance of a Functioning Chain Brake

The chain brake, often referred to as the chain brake or chain brake handle, serves as a safety mechanism designed to protect users from potential kickbacks and injuries. When engaged, it stops the chain from spinning, providing an essential layer of protection.

The chain brake is crucial for the following reasons:

  1. Kickback Prevention: In the event of kickback, which occurs when the chain strikes an object or pinches, the chain brake can stop the chain’s movement almost instantly, reducing the risk of injury.
  2. Emergency Stop: It allows you to halt the chain’s movement swiftly if you lose control or need to react to a sudden danger.
  3. Safety Compliance: Proper chain brake operation is often a legal requirement, especially in professional settings.

Diagnosing and Addressing Chain Brake Problems

Step 1: Safety First

Before diagnosing or addressing chain brake issues, ensure the chainsaw is turned off and take necessary safety precautions.

Step 2: Visual Inspection

Examine the chain brake handle for visible damage, wear, or loose parts. Check for any debris that might impede proper function.

Step 3: Handle Operation

Attempt to engage and disengage the chain brake handle. If it’s not responding correctly or if there’s resistance, there may be an issue with the mechanism.

Step 4: Tension Adjustment

Sometimes, chain brake problems can be resolved by adjusting the tension on the chain brake band. Consult your user manual for guidance on tension adjustments.

Step 5: Seek Professional Help

If you suspect significant internal issues with the chain brake mechanism, or if adjustments do not resolve the problem, consult a professional technician. They can assess and repair the chain brake system.

Maintenance Practices for a Reliable Chain Brake

  1. Regular Inspection: Routinely inspect the chain brake handle and mechanism for any visible wear, damage, or debris. Address any issues promptly.
  2. Tension Adjustment: Refer to your user manual for the manufacturer’s recommended chain brake band tension and make adjustments as needed.
  3. Lubrication: Some chain brake systems may benefit from occasional lubrication to ensure smooth operation. Consult your user manual for guidance on lubrication points.
  4. Professional Maintenance: Include regular professional maintenance in your chainsaw’s schedule to ensure that the chain brake and other safety features remain in optimal condition.

By emphasizing the importance of a functioning chain brake, diagnosing and addressing chain brake problems promptly, and following maintenance practices, you can ensure the safety and reliability of your Stihl MS 661 chainsaw. In the conclusion, we’ll recap the common problems and reiterate the significance of proactive troubleshooting and maintenance.

General Maintenance Tips

Maintaining your Stihl MS 661 chainsaw is the key to preventing common issues, extending its lifespan, and ensuring consistent, reliable performance. In this section, we’ll explore essential general maintenance tips, including routine maintenance to prevent common issues, proper storage and care of your chainsaw, and a suggested maintenance schedule.

Routine Maintenance to Prevent Common Issues

  1. Chain Maintenance: Regularly inspect the chain for sharpness and tension. Keep it sharp with proper filing, and adjust the tension as recommended by the manufacturer. A well-maintained chain ensures efficient cutting and prevents issues like poor performance and chain slippage.
  2. Air Filter Care: Clean or replace the air filter as needed. A clogged air filter can lead to poor performance and overheating. Regular air filter maintenance ensures proper airflow to the engine.
  3. Spark Plug Replacement: Follow the manufacturer’s recommendations for spark plug replacement, typically every 100 operating hours. A fresh spark plug helps maintain optimal ignition and performance.
  4. Lubrication System: Keep the chain and bar well-lubricated with the recommended chain oil. Check the oiling system for any issues and make adjustments as needed to avoid overheating and chain slippage.
  5. Fuel System: Use fresh, high-quality fuel with the correct oil-gasoline ratio. Avoid using stale fuel, which can cause starting problems and affect engine performance.
  6. Carburetor Adjustment: If you have experience with chainsaw maintenance, check the carburetor adjustment. However, it’s advisable to consult a professional technician to ensure it’s set correctly.

Proper Storage and Care of Your Stihl MS 661

  1. Cleanliness: After each use, clean your chainsaw, removing sawdust, dirt, and debris. Keeping it clean not only prolongs the chainsaw’s life but also helps prevent chain brake and overheating issues.
  2. Fuel Draining: If you won’t be using your chainsaw for an extended period, drain the fuel tank and run the chainsaw until it stops to prevent stale fuel from clogging the carburetor.
  3. Storage Position: Store your chainsaw in an upright position, preferably in a dry, cool place, and away from direct sunlight. This prevents oil and fuel leaks and prolongs the life of components.
  4. Chain and Bar Cover: Use a chain and bar cover when storing your chainsaw to protect the chain, bar, and yourself from accidental contact.

Suggested Maintenance Schedule

While the specific maintenance schedule can vary based on your usage and environmental conditions, here’s a general guideline to help you keep your Stihl MS 661 in top condition:

  • Daily or Before Each Use: Check chain tension and sharpness, inspect the air filter, and ensure proper chain and bar lubrication.
  • Weekly: Clean the chainsaw thoroughly, inspect the spark plug, and check for fuel and oil leaks.
  • Monthly: Check the carburetor adjustment, if you’re experienced. Otherwise, consult a professional for this task.
  • Every 20-25 Operating Hours: Consider a more comprehensive checkup with a technician, who can inspect the engine, carburetor, and other internal components.

By following these general maintenance tips and creating a maintenance schedule tailored to your usage, you can ensure the longevity and peak performance of your Stihl MS 661 chainsaw. Consistent care and maintenance are the keys to avoiding common problems and enjoying a reliable and safe cutting experience.


As we conclude our journey through the six most common Stihl MS 661 problems and their troubleshooting solutions, it’s essential to recap the key takeaways and emphasize the importance of regular maintenance. Let’s revisit the common problems, underscore the significance of proactive maintenance, and encourage all users to invest time in troubleshooting and maintenance for optimal performance.

Recap of the Common Stihl MS 661 Problems

Throughout this guide, we’ve explored the following common problems associated with the Stihl MS 661 chainsaw:

  1. Starting Issues: These can be caused by fuel problems, air filter issues, spark plug problems, and more.
  2. Poor Performance: Symptoms include reduced cutting power, overheating, and increased fuel consumption.
  3. Chain Slippage: Often caused by improper chain tension, worn bars or sprockets, or damaged drive links.
  4. Overheating: Recognizable by excessive heat, reduced performance, and occasional smoke or odors.
  5. Oil or Fuel Leaks: Types of leaks, including oil and fuel leaks, which can occur due to various reasons like damaged fuel lines, carburetor problems, and more.
  6. Chain Brake Failure: The importance of a functioning chain brake and how to diagnose, address, and maintain it.

Emphasis on the Importance of Regular Maintenance

Regular maintenance is the cornerstone of a reliable and efficient Stihl MS 661 chainsaw. By proactively addressing common problems and conducting routine maintenance, you can:

  • Enhance Safety: Ensure that your chainsaw operates safely, minimizing the risk of accidents.
  • Extend Lifespan: Regular maintenance prevents premature wear and tear, increasing the lifespan of your equipment.
  • Optimize Performance: A well-maintained chainsaw performs efficiently, saving you time and effort.
  • Save Money: Timely maintenance prevents costly repairs or replacements, making it a cost-effective choice.

Encouragement for Users to Troubleshoot and Maintain Their Chainsaws for Optimal Performance

We strongly encourage all Stihl MS 661 users to take an active role in troubleshooting and maintenance. By following the tips and guidelines provided in this guide, you can keep your chainsaw in top working condition. Here are some steps to get you started:

  1. Routine Inspections: Make it a habit to inspect your chainsaw before and after each use, checking for signs of wear and potential issues.
  2. Regular Cleaning: Keeping your chainsaw clean and free of debris not only maintains its appearance but also helps with optimal performance.
  3. Adhere to Maintenance Schedules: Follow the manufacturer’s recommended maintenance schedule, including periodic professional check-ups.
  4. Safety First: Always prioritize safety when performing maintenance. Ensure the chainsaw is turned off, and wear appropriate protective gear.
  5. Consult the Manual: Your user manual is a valuable resource for maintenance guidelines and troubleshooting. Keep it handy and refer to it when needed.

By investing time and effort into maintaining your Stihl MS 661 chainsaw, you’ll not only ensure its longevity but also enjoy consistent and reliable cutting performance. Troubleshooting and maintenance are the keys to a safer and more efficient chainsaw experience.

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