Stihl MS 391 Problems: Real-World Firewood Splitting Insights (5 Pro Tips)

The timeless pursuit of warmth and efficiency in firewood preparation often leads us to rely on robust tools like the Stihl MS 391 chainsaw. As someone who has spent years in the field, wrestling logs and perfecting the art of firewood splitting, I understand the frustrations that arise when your equipment doesn’t perform as expected. This guide is designed to address common Stihl MS 391 problems, offering real-world insights and five pro tips to enhance your firewood splitting endeavors. Let’s dive in and ensure your chainsaw remains a reliable partner in your wood processing journey.

Understanding Common Stihl MS 391 Problems

Over the years, I’ve encountered various issues with the Stihl MS 391. From starting problems to cutting inefficiencies, understanding these common pitfalls is the first step toward effective troubleshooting.

Starting Problems

One of the most frequent complaints I hear (and have experienced myself) revolves around starting the MS 391. This can manifest in several ways:

• Engine Refusal to Start: The engine simply won’t turn over, even after multiple attempts.
• Hard Starting: The chainsaw requires excessive pulling and effort to get it running.
• Intermittent Starting: The chainsaw starts sometimes but not others, creating unpredictable downtime.

Causes:

• Fuel Issues: Stale fuel, incorrect fuel mixture, or a clogged fuel filter can prevent the engine from receiving the necessary fuel. Ethanol-blended fuels are notorious for causing problems if left sitting for extended periods.
• Spark Plug Problems: A fouled, cracked, or improperly gapped spark plug can disrupt the ignition process.
• Air Filter Issues: A dirty or clogged air filter restricts airflow, leading to an improper air-fuel mixture.
• Carburetor Problems: A malfunctioning carburetor can prevent the correct air-fuel mixture from reaching the engine.
• Ignition Module Problems: A faulty ignition module can prevent the spark plug from firing.

Troubleshooting Steps:

1. Check the Fuel: Ensure you’re using fresh, high-quality fuel mixed at the correct ratio (typically 50:1 for the MS 391). Drain any old fuel and replace it with a fresh mixture. I always recommend using a fuel stabilizer if the chainsaw will be stored for more than a month.
2. Inspect the Spark Plug: Remove the spark plug and inspect it for fouling, cracks, or damage. Clean the plug with a wire brush or replace it if necessary. Check the gap using a spark plug gapping tool; the correct gap for the MS 391 is typically 0.020 inches (0.5 mm).
3. Examine the Air Filter: Remove the air filter and inspect it for dirt and debris. Clean the filter with warm, soapy water and allow it to dry completely before reinstalling. If the filter is heavily soiled or damaged, replace it.
4. Check the Carburetor: Visually inspect the carburetor for any signs of damage or fuel leakage. If you suspect a carburetor problem, you may need to have it professionally cleaned or rebuilt.
5. Test the Ignition Module: Use a spark tester to check if the ignition module is producing a spark. If there is no spark, the ignition module may need to be replaced.

Cutting Inefficiencies

Another common issue is a decrease in cutting performance. This can manifest as:

• Slow Cutting Speed: The chainsaw takes longer than usual to cut through wood.
• Chain Binding: The chain gets stuck or pinched in the wood during cutting.
• Uneven Cuts: The chainsaw produces cuts that are not straight or consistent.
• Excessive Vibration: The chainsaw vibrates excessively during operation, making it difficult to control.

Causes:

• Dull Chain: A dull or damaged chain is the most common cause of cutting inefficiencies.
• Incorrect Chain Tension: A chain that is too loose or too tight can cause binding and uneven cuts.
• Improper Bar Lubrication: Insufficient lubrication can cause the chain to overheat and bind.
• Worn Bar: A worn or damaged guide bar can cause the chain to run unevenly.
• Incorrect Cutting Technique: Using the wrong cutting technique can put unnecessary strain on the chainsaw and reduce its efficiency.

Troubleshooting Steps:

1. Sharpen the Chain: Sharpen the chain using a chainsaw file or a chain grinder. Ensure that the cutters are sharpened to the correct angle and depth. I typically sharpen my chain after every two tanks of fuel, or more often if I’m cutting dirty or abrasive wood.
2. Adjust Chain Tension: Adjust the chain tension so that it is snug against the guide bar but can still be pulled around by hand. The correct tension will vary depending on the type of wood you are cutting and the temperature. I usually aim for about 1/8 inch of sag on the bottom of the bar.
3. Check Bar Lubrication: Ensure that the bar oil reservoir is full and that the oiler is functioning properly. Check the oiler outlet on the guide bar for any blockages. I prefer to use a high-quality bar and chain oil specifically designed for chainsaws.
4. Inspect the Guide Bar: Check the guide bar for wear, damage, or burrs. Clean the bar with a wire brush and file down any burrs. If the bar is heavily worn or damaged, replace it.
5. Refine Cutting Technique: Use proper cutting techniques to avoid pinching and binding. Keep the chain moving and avoid forcing the chainsaw through the wood. Use the bumper spikes to maintain control and leverage.

Engine Problems

Beyond starting and cutting, the MS 391 can experience more general engine-related issues:

• Engine Stalling: The engine shuts off unexpectedly during operation.
• Loss of Power: The engine lacks its usual power and struggles to cut through wood.
• Overheating: The engine becomes excessively hot during operation.
• Excessive Smoke: The engine produces excessive smoke, which can indicate a problem with the fuel mixture or engine components.

Causes:

• Overheating: Overheating can be caused by a clogged air filter, a malfunctioning cooling fan, or running the engine at high speeds for extended periods.
• Incorrect Fuel Mixture: An incorrect fuel mixture can cause the engine to run poorly or stall.
• Carburetor Problems: A malfunctioning carburetor can cause the engine to run lean or rich.
• Worn Piston Rings: Worn piston rings can cause a loss of compression and power.
• Damaged Cylinder: A damaged cylinder can cause a loss of compression and power.

Troubleshooting Steps:

1. Check for Overheating: Allow the engine to cool down completely. Check the air filter and cooling fan for any blockages. Ensure that the engine is properly lubricated.
2. Verify Fuel Mixture: Ensure that you are using the correct fuel mixture (typically 50:1 for the MS 391). Drain any old fuel and replace it with a fresh mixture.
3. Inspect the Carburetor: Visually inspect the carburetor for any signs of damage or fuel leakage. If you suspect a carburetor problem, you may need to have it professionally cleaned or rebuilt.
4. Check Compression: Use a compression tester to check the engine’s compression. Low compression can indicate worn piston rings or a damaged cylinder.
5. Seek Professional Help: If you are unable to diagnose or repair the engine problem yourself, consult a qualified chainsaw mechanic.

5 Pro Tips for Firewood Splitting with the Stihl MS 391

Now that we’ve covered common problems, let’s delve into five pro tips to maximize your firewood splitting efficiency with the Stihl MS 391. These tips are based on years of experience and are designed to improve your technique, safety, and overall productivity.

Tip 1: Mastering the Hinge Cut for Controlled Felling

The hinge cut is a fundamental technique in felling trees safely and predictably. A properly executed hinge cut controls the direction of the fall, preventing the tree from kicking back or falling in an unintended direction.

Why it Matters:

• Safety: Prevents the tree from falling on you or other objects.
• Control: Allows you to direct the tree’s fall for easier processing.
• Efficiency: Reduces the risk of the tree getting hung up on other trees.

How to Execute a Hinge Cut:

1. Plan Your Cut: Determine the desired direction of fall and clear any obstacles in the path.
2. Make the Face Cut: Cut a notch on the side of the tree facing the desired direction of fall. The notch should be about 1/3 of the tree’s diameter. I typically use a 45-degree angle for the top cut and a 90-degree angle for the bottom cut.
3. Make the Back Cut: Cut from the opposite side of the tree, slightly above the bottom of the face cut. Leave a hinge of wood (about 10% of the tree’s diameter) connecting the two cuts. This hinge will guide the tree’s fall.
4. Drive Wedges: Insert wedges into the back cut to help push the tree over in the desired direction.
5. Final Cut: If necessary, make a final cut through the hinge to complete the felling process.

Real-World Example:

I once had to fell a large oak tree in a densely wooded area. By carefully planning the hinge cut and using wedges, I was able to direct the tree’s fall away from a nearby house and into an open area. This saved me a lot of time and effort in processing the tree into firewood.

Metrics:

• Hinge Size: Aim for a hinge that is approximately 10% of the tree’s diameter.
• Face Cut Depth: Make the face cut about 1/3 of the tree’s diameter.
• Wedge Force: Use enough force with the wedges to overcome the tree’s natural resistance.

Takeaway: Mastering the hinge cut is essential for safe and efficient tree felling. Practice this technique until you are comfortable with it.

Tip 2: Optimizing Bucking Techniques for Different Wood Types

Bucking is the process of cutting felled trees into manageable lengths for firewood splitting. Different wood types require different bucking techniques to maximize efficiency and minimize strain on your chainsaw.

Why it Matters:

• Efficiency: Reduces the amount of time and effort required to process firewood.
• Safety: Prevents the log from pinching the chain or kicking back.
• Tool Longevity: Minimizes wear and tear on your chainsaw.

Bucking Techniques for Different Wood Types:

• Softwoods (Pine, Fir, Spruce): Softwoods are generally easier to cut than hardwoods. Use a standard bucking technique, making sure to support the log to prevent pinching. I typically use a sawbuck to elevate the log and provide support.
• Hardwoods (Oak, Maple, Ash): Hardwoods are denser and more difficult to cut. Use a step-cut technique, making multiple shallow cuts to avoid pinching. I also recommend using a longer guide bar for hardwoods to provide more leverage.
• Tension Wood (Wood Under Stress): Tension wood is wood that is under compression or tension, often found in leaning trees or trees that have been subjected to wind. Use a relief cut to release the tension before making the final cut. I always approach tension wood with caution, as it can be unpredictable.

Real-World Example:

I once tried to buck a large oak log without using a step-cut technique. The chain quickly became pinched, and I had to struggle to free it. After switching to the step-cut technique, I was able to buck the log much more easily and safely.

Metrics:

• Cut Depth: For step-cuts, make each cut about 1/3 of the log’s diameter.
• Support Spacing: Place supports (sawbucks, logs) every 4-6 feet for long logs.
• Relief Cut Depth: Make the relief cut about 1/4 of the log’s diameter.

Takeaway: Adapting your bucking technique to the type of wood you are cutting can significantly improve your efficiency and safety.

Tip 3: Utilizing Wedges and Levers for Stuck Logs

Sometimes, even with the best bucking techniques, logs can become stuck or pinched. Using wedges and levers can help you free the log and continue processing.

Why it Matters:

• Efficiency: Prevents you from wasting time and energy struggling with stuck logs.
• Safety: Reduces the risk of injury from forcing the chainsaw or log.
• Tool Protection: Prevents damage to your chainsaw from excessive strain.

How to Use Wedges and Levers:

1. Identify the Pinch Point: Determine where the log is being pinched.
2. Insert Wedges: Drive wedges into the cut to create space and relieve the pressure. I typically use a combination of plastic and steel wedges, depending on the size and weight of the log.
3. Use a Lever: Use a lever (such as a peavey or a log jack) to lift or roll the log, further relieving the pressure. I find a log jack particularly useful for lifting heavy logs off the ground.
4. Continue Cutting: Once the log is freed, continue cutting.

Real-World Example:

I was once bucking a large maple log when the chain became severely pinched. I tried pulling and prying, but nothing worked. Finally, I inserted two wedges into the cut and used a peavey to roll the log slightly. The chain popped free instantly, and I was able to finish bucking the log without further problems.

Metrics:

• Wedge Angle: Use wedges with a gradual angle for maximum lifting power.
• Leverage Ratio: Use a lever with a sufficient length to provide adequate leverage.
• Wedge Placement: Position wedges close to the pinch point for maximum effectiveness.

Takeaway: Wedges and levers are essential tools for freeing stuck logs and preventing damage to your chainsaw.

Tip 4: Mastering Chain Sharpening for Peak Performance

A sharp chain is crucial for efficient and safe firewood splitting. Mastering chain sharpening techniques will not only improve your cutting speed but also extend the life of your chainsaw.

Why it Matters:

• Efficiency: A sharp chain cuts faster and requires less effort.
• Safety: A sharp chain is less likely to kick back or bind.
• Tool Longevity: A sharp chain reduces strain on the engine and other components.

Chain Sharpening Techniques:

1. Gather Your Tools: You will need a chainsaw file, a file guide, a depth gauge tool, and a vise to hold the chain steady. I prefer to use a chainsaw file kit that includes all the necessary tools.
2. Secure the Chain: Secure the chain in a vise or clamp to prevent it from moving during sharpening.
3. Sharpen the Cutters: Use the chainsaw file and file guide to sharpen each cutter to the correct angle and depth. I typically use a 30-degree angle for the top plate and a 60-degree angle for the side plate.
4. Check the Depth Gauges: Use the depth gauge tool to check the height of the depth gauges. If the depth gauges are too high, file them down slightly. I typically set the depth gauges to 0.025 inches (0.6 mm) below the top of the cutter.
5. Test the Chain: After sharpening, test the chain by cutting through a piece of wood. The chain should cut smoothly and efficiently.

Real-World Example:

I used to struggle with dull chains and slow cutting speeds. After learning how to properly sharpen my chain, I was amazed at the difference it made. My cutting speed increased dramatically, and I no longer had to struggle to cut through wood.

Metrics:

• File Angle: Use the correct file angle for your chain type (typically 30 degrees for the top plate and 60 degrees for the side plate).
• Depth Gauge Height: Set the depth gauges to the correct height (typically 0.025 inches (0.6 mm) below the top of the cutter).
• Sharpening Frequency: Sharpen your chain after every two tanks of fuel, or more often if you are cutting dirty or abrasive wood.

Takeaway: Mastering chain sharpening is essential for maintaining peak chainsaw performance. Practice this technique regularly to keep your chain sharp and efficient.

Tip 5: Implementing Safe Wood Stacking and Drying Practices

Proper wood stacking and drying are crucial for producing high-quality firewood. Dry firewood burns hotter, cleaner, and more efficiently than wet or green firewood.

Why it Matters:

• Efficiency: Dry firewood burns hotter and produces more heat.
• Safety: Dry firewood produces less smoke and creosote, reducing the risk of chimney fires.
• Environmental Impact: Dry firewood burns cleaner and produces fewer emissions.

Wood Stacking and Drying Practices:

1. Choose a Sunny and Windy Location: Select a location that receives plenty of sunlight and is exposed to wind. This will help to evaporate moisture from the wood.
2. Elevate the Wood: Stack the wood on pallets or other supports to elevate it off the ground. This will allow air to circulate underneath the wood and prevent moisture from wicking up from the ground.
3. Stack the Wood Loosely: Stack the wood loosely to allow air to circulate between the logs. I typically stack the wood in rows, leaving a few inches of space between each row.
4. Cover the Top: Cover the top of the wood pile with a tarp or other waterproof material to protect it from rain and snow. Leave the sides of the pile uncovered to allow for ventilation.
5. Allow Sufficient Drying Time: Allow the wood to dry for at least six months, or preferably a year, before burning it. The drying time will vary depending on the type of wood and the climate.

Real-World Example:

I used to burn green firewood, and it was a constant struggle to keep the fire going. The wood produced a lot of smoke and creosote, and I had to clean my chimney frequently. After switching to dry firewood, I noticed a significant improvement in the efficiency and cleanliness of my fires.

Metrics:

• Moisture Content: Aim for a moisture content of less than 20% before burning the wood. Use a moisture meter to check the moisture content of the wood.
• Drying Time: Allow the wood to dry for at least six months, or preferably a year.
• Stack Height: Stack the wood no higher than 4 feet to prevent it from collapsing.

Takeaway: Proper wood stacking and drying are essential for producing high-quality firewood. Follow these practices to ensure that your firewood burns hotter, cleaner, and more efficiently.

Advanced Troubleshooting and Maintenance

Beyond the basics, understanding advanced troubleshooting and maintenance can significantly extend the life and performance of your Stihl MS 391.

Carburetor Adjustments

The carburetor is a critical component that regulates the air-fuel mixture. Improper carburetor settings can lead to starting problems, poor performance, and engine damage.

Understanding Carburetor Settings:

• Low-Speed Jet (L): Controls the air-fuel mixture at idle and low speeds.
• High-Speed Jet (H): Controls the air-fuel mixture at high speeds.
• Idle Speed Screw (LA): Adjusts the engine’s idle speed.

Adjusting the Carburetor:

1. Warm Up the Engine: Start the engine and allow it to warm up for a few minutes.
2. Adjust the Low-Speed Jet: Turn the low-speed jet screw clockwise until the engine starts to stumble or stall. Then, turn the screw counterclockwise until the engine runs smoothly at idle.
3. Adjust the High-Speed Jet: Run the engine at full throttle and listen for any signs of hesitation or surging. Adjust the high-speed jet screw until the engine runs smoothly at full throttle.
4. Adjust the Idle Speed Screw: Adjust the idle speed screw until the engine idles smoothly without stalling. The correct idle speed for the MS 391 is typically around 2,800 RPM.

Real-World Example:

I once had a Stihl MS 391 that was running poorly and stalling frequently. After adjusting the carburetor, the engine ran much smoother and more efficiently.

Metrics:

• Idle Speed: Aim for an idle speed of around 2,800 RPM.
• High-Speed Performance: Ensure that the engine runs smoothly at full throttle without hesitation or surging.
• Low-Speed Performance: Ensure that the engine runs smoothly at idle without stalling.

Takeaway: Proper carburetor adjustments can significantly improve the performance and reliability of your Stihl MS 391.

Diagnosing and Repairing Fuel System Problems

Fuel system problems are a common cause of starting and performance issues. Understanding how to diagnose and repair these problems can save you time and money.

Common Fuel System Problems:

• Clogged Fuel Filter: A clogged fuel filter can restrict fuel flow and cause the engine to stall.
• Damaged Fuel Lines: Damaged fuel lines can leak fuel and cause the engine to run poorly.
• Malfunctioning Fuel Pump: A malfunctioning fuel pump can prevent fuel from reaching the carburetor.

Diagnosing Fuel System Problems:

1. Check the Fuel Filter: Remove the fuel filter and inspect it for dirt and debris. Replace the filter if it is clogged.
2. Inspect the Fuel Lines: Inspect the fuel lines for any cracks, leaks, or damage. Replace any damaged fuel lines.
3. Test the Fuel Pump: Disconnect the fuel line from the carburetor and crank the engine. If fuel does not flow from the fuel line, the fuel pump may be malfunctioning.

Repairing Fuel System Problems:

1. Replace the Fuel Filter: Install a new fuel filter.
2. Replace Damaged Fuel Lines: Replace any damaged fuel lines with new fuel lines.
3. Replace the Fuel Pump: If the fuel pump is malfunctioning, replace it with a new fuel pump.

Real-World Example:

I once had a Stihl MS 391 that was refusing to start. After checking the fuel system, I discovered that the fuel filter was completely clogged. After replacing the fuel filter, the chainsaw started right up.

Metrics:

• Fuel Flow Rate: Ensure that the fuel pump is delivering fuel at the correct flow rate.
• Fuel Line Condition: Inspect the fuel lines regularly for any signs of damage or wear.
• Fuel Filter Replacement Interval: Replace the fuel filter every 50 hours of operation, or more often if you are using dirty fuel.

Takeaway: Diagnosing and repairing fuel system problems can restore your Stihl MS 391 to optimal performance.

Maintaining Optimal Engine Cooling

Overheating can cause serious damage to your chainsaw engine. Maintaining optimal engine cooling is essential for preventing overheating and extending the life of your chainsaw.

Causes of Overheating:

• Clogged Air Filter: A clogged air filter restricts airflow and can cause the engine to overheat.
• Dirty Cooling Fins: Dirty cooling fins can prevent heat from dissipating properly.
• Malfunctioning Cooling Fan: A malfunctioning cooling fan can prevent air from circulating around the engine.

Maintaining Optimal Engine Cooling:

1. Clean the Air Filter: Clean the air filter regularly to ensure proper airflow.
2. Clean the Cooling Fins: Clean the cooling fins with a brush or compressed air to remove dirt and debris.
3. Inspect the Cooling Fan: Inspect the cooling fan for any damage or blockages. Replace the cooling fan if it is damaged.

Real-World Example:

I once had a Stihl MS 391 that was overheating frequently. After cleaning the cooling fins and replacing the air filter, the engine ran much cooler and more efficiently.

Metrics:

• Engine Temperature: Monitor the engine temperature to ensure that it is within the normal operating range.
• Air Filter Cleaning Interval: Clean the air filter every 25 hours of operation, or more often if you are working in dusty conditions.
• Cooling Fin Cleaning Interval: Clean the cooling fins every 50 hours of operation.

Takeaway: Maintaining optimal engine cooling is essential for preventing overheating and extending the life of your Stihl MS 391.

Safety Considerations

No discussion of chainsaw operation is complete without emphasizing safety. Chainsaws are powerful tools, and it’s crucial to follow safety guidelines to prevent accidents.

Personal Protective Equipment (PPE)

Always wear appropriate PPE when operating a chainsaw:

• Chainsaw Chaps: Protect your legs from cuts.
• Safety Glasses or Face Shield: Protect your eyes from flying debris.
• Hearing Protection: Protect your ears from the loud noise of the chainsaw.
• Gloves: Protect your hands and improve grip.
• Steel-Toed Boots: Protect your feet from falling logs and other hazards.

Safe Operating Practices

• Read the Owner’s Manual: Familiarize yourself with the chainsaw’s operating instructions and safety precautions.
• Maintain a Safe Distance: Keep bystanders at least 50 feet away from the cutting area.
• Work in a Clear Area: Clear the cutting area of any obstacles, such as rocks, branches, or debris.
• Use Proper Cutting Techniques: Use proper cutting techniques to avoid kickback and other hazards.
• Never Cut Above Shoulder Height: Cutting above shoulder height is dangerous and can lead to loss of control.
• Never Cut in Unsafe Conditions: Avoid cutting in wet, windy, or icy conditions.
• Inspect the Chainsaw Regularly: Inspect the chainsaw before each use for any signs of damage or wear.
• Take Breaks: Take frequent breaks to avoid fatigue.
• Stay Sober: Never operate a chainsaw under the influence of alcohol or drugs.

Understanding and Preventing Kickback

Kickback is a sudden and dangerous reaction that can occur when the tip of the chainsaw bar comes into contact with an object. Kickback can cause the chainsaw to be thrown back towards the operator, resulting in serious injury.

Preventing Kickback:

• Use a Chainsaw with a Low-Kickback Chain: Low-kickback chains are designed to reduce the risk of kickback.
• Avoid Contact with the Tip of the Bar: Be aware of the position of the tip of the bar and avoid contacting it with any objects.
• Maintain a Firm Grip: Maintain a firm grip on the chainsaw with both hands.
• Stand to the Side of the Cut: Stand to the side of the cut to avoid being hit by the chainsaw if kickback occurs.

Conclusion

The Stihl MS 391 is a reliable and powerful chainsaw that can be a valuable asset for firewood splitting. By understanding common problems, implementing pro tips, and following safety guidelines, you can maximize your efficiency, safety, and overall success in your wood processing endeavors. Remember to prioritize maintenance, use the right techniques for different wood types, and always wear appropriate PPE. With these insights, you’ll be well-equipped to tackle any firewood splitting project with confidence and skill.

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