Stihl Chainsaw MS291 Tune-Up Tips (5 Pro Engine Fixes)

The rough, satisfying grit of sawdust clinging to my gloves. The sharp, clean scent of freshly cut wood filling the air. The rhythmic roar of a well-tuned chainsaw biting into timber. These are the sensations that fuel my passion for wood processing, and they all hinge on one crucial element: a properly maintained chainsaw. In this guide, I’ll share my experience and insights on tuning up a Stihl MS291 chainsaw, focusing on five pro engine fixes that will keep your saw running smoothly and efficiently. Having spent countless hours felling trees, bucking logs, and preparing firewood, I’ve learned that a reliable chainsaw is indispensable. Let’s dive in and ensure your MS291 is always ready to tackle the toughest jobs.

Stihl Chainsaw MS291 Tune-Up Tips: 5 Pro Engine Fixes

The Stihl MS291 is a workhorse of a chainsaw, known for its reliability and power. However, like any machine, it requires regular maintenance to perform at its best. Tuning up your MS291 isn’t just about keeping it running; it’s about maximizing its lifespan, improving its efficiency, and ensuring your safety. These five engine fixes are based on my years of experience, and they’ll help you keep your MS291 in top condition.

1. Carburetor Adjustment: Fine-Tuning for Peak Performance

The carburetor is the heart of your MS291’s engine, responsible for mixing air and fuel in the correct proportions. A poorly adjusted carburetor can lead to a variety of problems, including difficult starting, poor idling, reduced power, and excessive fuel consumption. I can’t tell you how many times I’ve seen a perfectly good chainsaw sidelined by a simple carburetor issue.

Understanding the Carburetor Screws

The carburetor on the Stihl MS291 typically has three adjustment screws:

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

Before making any adjustments, it’s crucial to understand what each screw does and how it affects the engine’s performance.

Step-by-Step Carburetor Adjustment Process

1. Preparation:

Safety First: Wear safety glasses and gloves. Ensure the chainsaw is on a stable surface and the chain brake is engaged.
Warm-Up: Start the chainsaw and let it run for a few minutes to warm up the engine.
Locate the Screws: Identify the L, H, and LA adjustment screws on the carburetor.

2. Initial Settings:

Factory Settings: Consult your Stihl MS291 owner’s manual for the factory settings for the L and H screws. These are typically expressed as turns out from the fully closed position. As a general rule, start with the L and H screws turned out one full turn.
Fine-Tuning: These factory settings are a starting point and may need to be adjusted based on your altitude, temperature, and fuel type.

3. Adjusting the Low-Speed (L) Screw:

Idle Speed: Turn the L screw clockwise to lean the mixture (less fuel) or counterclockwise to richen the mixture (more fuel).
Listen to the Engine: Aim for a smooth, consistent idle without stalling or excessive smoke.
Fine-Tuning: If the engine stalls easily or hesitates when you accelerate, the mixture is likely too lean. If the engine idles roughly or produces excessive smoke, the mixture is likely too rich.
Idle Speed Optimization: A properly adjusted low-speed circuit will allow the engine to transition smoothly from idle to full throttle.

4. Adjusting the High-Speed (H) Screw:

Full Throttle: With the chain brake engaged, carefully run the chainsaw at full throttle for a few seconds.
Listen to the Engine: The engine should run smoothly and powerfully without sputtering or bogging down.
Fine-Tuning: Turn the H screw clockwise to lean the mixture or counterclockwise to richen the mixture.
Engine Protection: Avoid running the engine too lean, as this can cause overheating and damage. A slightly rich mixture is generally safer.
Professional Tip: Experienced chainsaw users can often hear when the high-speed mixture is correct. A slight “four-stroking” sound at full throttle indicates a slightly rich mixture, which is ideal.

5. Adjusting the Idle Speed (LA) Screw:

Chain Movement: The goal is to set the idle speed so that the chain does not move when the engine is idling.
Adjustment: Turn the LA screw clockwise to increase the idle speed or counterclockwise to decrease it.
Final Check: After adjusting the LA screw, double-check that the chain remains stationary at idle.

6. Final Testing:

Test Cuts: Make a few test cuts to ensure the chainsaw is performing optimally under load.
Re-Adjustment: If necessary, make small adjustments to the L and H screws to fine-tune the performance.

Data and Metrics

Idle Speed: The ideal idle speed for the Stihl MS291 is typically around 2,800 RPM. Use a tachometer to accurately measure the idle speed.
Fuel Consumption: A properly tuned carburetor can improve fuel efficiency by up to 15%.
Exhaust Emissions: A lean-running engine produces higher levels of harmful emissions. Tuning the carburetor can help reduce emissions and improve air quality.

Troubleshooting Carburetor Issues

Engine Stalling: This can be caused by a lean mixture, a clogged fuel filter, or a faulty spark plug.
Poor Idle: This can be caused by an incorrect idle speed setting, a vacuum leak, or a dirty carburetor.
Reduced Power: This can be caused by a rich mixture, a clogged air filter, or a worn piston ring.

Real-World Example

I once worked with a logger who was struggling with a Stihl MS291 that kept stalling in the middle of cuts. After checking the fuel filter and spark plug, I discovered that the carburetor was severely out of adjustment. The L screw was turned in almost all the way, resulting in a dangerously lean mixture. After carefully adjusting the carburetor according to the steps outlined above, the chainsaw ran like new, and the logger was able to resume his work without any further issues.

Takeaway

Proper carburetor adjustment is essential for maintaining the performance and longevity of your Stihl MS291. By understanding the function of each adjustment screw and following the step-by-step process outlined above, you can fine-tune your chainsaw for peak performance.

2. Fuel System Inspection and Maintenance: Ensuring a Clean and Consistent Fuel Supply

The fuel system is the lifeline of your chainsaw, delivering the necessary fuel to the engine. A clean and well-maintained fuel system is crucial for reliable starting, smooth running, and optimal performance. Over the years, I’ve seen countless chainsaws suffer from fuel-related issues, often due to neglect and lack of proper maintenance.

Components of the Fuel System

The fuel system of the Stihl MS291 consists of several key components:

Fuel Tank: Stores the fuel mixture.
Fuel Filter: Filters out debris and contaminants from the fuel.
Fuel Line: Carries fuel from the tank to the carburetor.
Carburetor: Mixes fuel and air in the correct proportions.
Fuel Cap: Seals the fuel tank and prevents leaks.

Step-by-Step Fuel System Inspection and Maintenance

1. Fuel Filter Replacement:

Frequency: Replace the fuel filter every 3 months or 50 hours of use, or more frequently if you use low-quality fuel.
Procedure:
- Empty the fuel tank.
- Use a hooked wire or pliers to pull the fuel filter out of the tank.
- Disconnect the fuel line from the old filter.
- Connect the fuel line to the new filter.
- Insert the new filter into the tank.

2. Fuel Line Inspection:

Check for Cracks and Leaks: Inspect the fuel line for cracks, leaks, and signs of deterioration. Replace the fuel line if it is damaged.
Fuel Line Replacement:
- Disconnect the fuel line from the fuel tank and carburetor.
- Install a new fuel line of the correct size and length.
- Ensure the fuel line is securely connected to the fuel tank and carburetor.

3. Fuel Tank Cleaning:

Frequency: Clean the fuel tank every 6 months or annually, depending on usage and fuel quality.
Procedure:
- Empty the fuel tank completely.
- Remove the fuel filter and fuel line.
- Rinse the fuel tank with clean fuel or a fuel tank cleaner.
- Allow the fuel tank to dry completely before reinstalling the fuel filter and fuel line.

4. Fuel Cap Inspection:

Check for Leaks: Inspect the fuel cap for leaks and ensure it is properly sealed.
Ventilation: Ensure the fuel cap vent is clear and functioning properly. A clogged vent can create a vacuum in the fuel tank, preventing fuel from flowing to the carburetor.
Fuel Cap Replacement: Replace the fuel cap if it is damaged or not sealing properly.

5. Using Fresh Fuel:

Fuel Storage: Store fuel in a clean, airtight container.
Fuel Stabilizer: Add a fuel stabilizer to the fuel mixture to prevent it from deteriorating.
Shelf Life: Use fuel within 30 days of mixing. Old fuel can become stale and cause starting and performance problems. I usually write the date of mixing directly on my fuel can to avoid any confusion.

Data and Metrics

Fuel Filter Pore Size: Use a fuel filter with a pore size of 10-20 microns to effectively filter out debris without restricting fuel flow.
Fuel Line Diameter: Use a fuel line with an inner diameter of 3/32″ for the Stihl MS291.
Fuel Mixture Ratio: Use a fuel mixture ratio of 50:1 (fuel to oil) for the Stihl MS291.

Troubleshooting Fuel System Issues

Difficult Starting: This can be caused by a clogged fuel filter, a blocked fuel line, or stale fuel.
Engine Stalling: This can be caused by a fuel starvation issue, a vacuum leak, or a faulty fuel pump.
Reduced Power: This can be caused by a restricted fuel flow, a dirty carburetor, or a worn piston ring.

Real-World Example

I remember helping a friend who was having trouble starting his Stihl MS291. After checking the spark plug and carburetor, I discovered that the fuel filter was completely clogged with debris. The filter was so blocked that it was preventing fuel from flowing to the carburetor. After replacing the fuel filter with a new one, the chainsaw started immediately and ran perfectly.

Takeaway

Regular inspection and maintenance of the fuel system are crucial for ensuring the reliable performance of your Stihl MS291. By replacing the fuel filter, inspecting the fuel line, cleaning the fuel tank, and using fresh fuel, you can prevent fuel-related issues and keep your chainsaw running smoothly.

3. Ignition System Check: Spark Plug and Ignition Coil Inspection

The ignition system is responsible for igniting the air-fuel mixture in the engine, creating the combustion that powers the chainsaw. A properly functioning ignition system is essential for reliable starting and smooth running. Over time, the spark plug and ignition coil can wear out or become damaged, leading to ignition problems. I’ve learned that a simple spark plug replacement can often resolve a host of starting and performance issues.

Components of the Ignition System

The ignition system of the Stihl MS291 consists of two main components:

Spark Plug: Creates the spark that ignites the air-fuel mixture.
Ignition Coil: Generates the high-voltage electricity needed to create the spark.

Step-by-Step Ignition System Check

1. Spark Plug Inspection:

Frequency: Inspect the spark plug every 25 hours of use or at least once a year.
Procedure:
- Remove the spark plug from the cylinder head using a spark plug wrench.
- Inspect the spark plug for signs of wear, damage, or fouling.
- Check the spark plug gap using a feeler gauge. The correct gap for the Stihl MS291 is typically 0.020 inches (0.5 mm).
- Clean the spark plug with a wire brush or spark plug cleaner.
- Replace the spark plug if it is worn, damaged, or fouled.

2. Spark Plug Replacement:

Recommended Spark Plug: The recommended spark plug for the Stihl MS291 is typically an NGK BPMR7A or a Champion RCJ6Y.
Procedure:
- Install a new spark plug of the correct type.
- Tighten the spark plug to the manufacturer’s recommended torque specification. This is typically around 11-15 ft-lbs (15-20 Nm).
- Do not overtighten the spark plug, as this can damage the cylinder head.

3. Ignition Coil Inspection:

Check for Damage: Inspect the ignition coil for cracks, breaks, or other signs of damage.
Test for Spark:
- Remove the spark plug and connect it to the spark plug wire.
- Ground the spark plug against the cylinder head.
- Pull the starter cord and observe the spark plug for a strong, blue spark.
- If there is no spark or the spark is weak and yellow, the ignition coil may be faulty.

4. Ignition Coil Replacement:

Procedure:
- Disconnect the spark plug wire from the spark plug.
- Remove the screws or bolts that secure the ignition coil to the engine.
- Disconnect the wiring harness from the ignition coil.
- Install a new ignition coil of the correct type.
- Connect the wiring harness to the new ignition coil.
- Secure the ignition coil to the engine with the screws or bolts.
- Connect the spark plug wire to the spark plug.

Data and Metrics

Spark Plug Gap: The correct spark plug gap for the Stihl MS291 is 0.020 inches (0.5 mm).
Spark Plug Torque: Tighten the spark plug to 11-15 ft-lbs (15-20 Nm).
Ignition Coil Resistance: Use a multimeter to measure the resistance of the ignition coil. The primary resistance should be between 0.5 and 1.5 ohms, and the secondary resistance should be between 3,000 and 5,000 ohms.

Troubleshooting Ignition System Issues

Difficult Starting: This can be caused by a faulty spark plug, a weak ignition coil, or a broken spark plug wire.
Engine Misfiring: This can be caused by a fouled spark plug, a cracked ignition coil, or a loose spark plug wire.
No Spark: This can be caused by a faulty ignition coil, a broken spark plug wire, or a short circuit in the ignition system.

Real-World Example

I once encountered a Stihl MS291 that would start and run for a few minutes, then suddenly shut off. After checking the fuel system and carburetor, I suspected an ignition problem. I removed the spark plug and found that it was heavily fouled with carbon deposits. After cleaning the spark plug and re-gapping it, the chainsaw ran perfectly.

Takeaway

Regular inspection and maintenance of the ignition system are crucial for ensuring the reliable starting and smooth running of your Stihl MS291. By inspecting the spark plug, checking the spark plug gap, and testing the ignition coil, you can identify and resolve ignition problems before they cause serious issues.

4. Air Filter Cleaning and Replacement: Maintaining Optimal Airflow for Combustion

The air filter is a critical component of your chainsaw’s engine, responsible for preventing dirt, dust, and debris from entering the carburetor and cylinder. A clean air filter ensures optimal airflow, which is essential for efficient combustion and peak performance. I’ve found that neglecting the air filter is one of the most common mistakes chainsaw users make, leading to a host of engine problems.

Types of Air Filters

The Stihl MS291 typically uses a felt or nylon mesh air filter. These filters are designed to be reusable and can be cleaned multiple times before needing to be replaced.

Step-by-Step Air Filter Cleaning and Replacement

1. Air Filter Removal:

Access: Locate the air filter cover on the chainsaw.
Removal: Remove the air filter cover by unscrewing the retaining knob or clip.
Extraction: Carefully remove the air filter from the housing.

2. Air Filter Cleaning:

Dry Cleaning: Gently tap the air filter against a hard surface to remove loose dirt and debris.
Compressed Air: Use compressed air to blow out any remaining dirt and debris from the inside out.
Washing (If Necessary): If the air filter is heavily soiled, wash it with warm soapy water. Rinse thoroughly and allow to dry completely before reinstalling.
Inspection: After cleaning, inspect the air filter for tears, holes, or other damage. Replace the air filter if it is damaged.

3. Air Filter Replacement:

Frequency: Replace the air filter every 6 months or annually, depending on usage and environmental conditions.
Procedure:
- Install a new air filter of the correct type.
- Ensure the air filter is properly seated in the housing.
- Reinstall the air filter cover and secure it with the retaining knob or clip.

4. Air Filter Housing Cleaning:

Procedure:
- Use a brush or cloth to clean the air filter housing and remove any dirt or debris.
- Ensure the air filter housing is clean and free of obstructions before reinstalling the air filter.

Data and Metrics

Air Filter Pore Size: Use an air filter with a pore size of 40-60 microns to effectively filter out dirt and debris without restricting airflow.
Airflow Restriction: A dirty air filter can restrict airflow by up to 50%, leading to reduced engine power and increased fuel consumption.
Filter Cleaning Frequency: Clean the air filter every 10 hours of use or more frequently in dusty conditions.

Troubleshooting Air Filter Issues

Reduced Power: This can be caused by a dirty air filter restricting airflow to the engine.
Engine Stalling: This can be caused by a severely clogged air filter starving the engine of air.
Difficult Starting: This can be caused by a dirty air filter preventing the engine from drawing in enough air to start.

Real-World Example

I was once helping a friend who was using his Stihl MS291 to clear brush in a very dusty area. After a few hours of use, the chainsaw started to lose power and eventually stalled. I checked the air filter and found that it was completely clogged with dust and debris. After cleaning the air filter, the chainsaw ran perfectly.

Takeaway

Regular cleaning and replacement of the air filter are crucial for maintaining the performance and longevity of your Stihl MS291. By cleaning the air filter regularly and replacing it when necessary, you can ensure optimal airflow to the engine and prevent a variety of performance problems.

5. Cylinder and Piston Inspection: Assessing Engine Health and Compression

The cylinder and piston are the heart of your chainsaw’s engine, responsible for generating the power that drives the chain. Over time, these components can wear out or become damaged, leading to reduced power, poor performance, and eventually, engine failure. A compression test can give you a good indication of the overall health of your engine. I’ve learned that early detection of cylinder and piston problems can save you from costly repairs down the road.

Signs of Cylinder and Piston Wear

Reduced Power: The chainsaw may lack its usual power and struggle to cut through wood.
Difficult Starting: The chainsaw may be difficult to start, especially when cold.
Low Compression: A compression test will reveal low compression readings.
Excessive Smoke: The chainsaw may produce excessive smoke, especially when running at high speeds.
Unusual Noises: The engine may make unusual noises, such as knocking or rattling.

Step-by-Step Cylinder and Piston Inspection

1. Compression Test:

Purpose: A compression test measures the amount of pressure the engine can generate in the cylinder. Low compression indicates wear or damage to the cylinder, piston, or piston rings.
Procedure:
- Remove the spark plug from the cylinder head.
- Install a compression tester into the spark plug hole.
- Pull the starter cord several times to crank the engine.
- Record the compression reading on the tester.
- Compare the reading to the manufacturer’s specifications. The Stihl MS291 typically has a compression reading of 120-150 PSI.

2. Cylinder Inspection:

Visual Inspection: Remove the muffler and inspect the cylinder walls for scratches, scoring, or other damage.
Port Inspection: Inspect the intake and exhaust ports for carbon buildup or obstructions.
Tools: A borescope can be used to inspect the cylinder walls more closely without disassembling the engine.

3. Piston Inspection:

Visual Inspection: Remove the cylinder head and inspect the piston for scratches, scoring, or other damage.
Ring Inspection: Inspect the piston rings for wear or damage. Check the ring end gap using a feeler gauge.
Piston Skirt: Check the piston skirt for signs of wear or collapse.

4. Cylinder and Piston Replacement:

When to Replace: Replace the cylinder and piston if they are severely worn, damaged, or scored.
Procedure:
- Disassemble the engine.
- Remove the old cylinder and piston.
- Install a new cylinder and piston of the correct type.
- Reassemble the engine.
- Follow the manufacturer’s instructions for break-in and lubrication.

Data and Metrics

Compression Reading: The Stihl MS291 typically has a compression reading of 120-150 PSI.
Ring End Gap: The piston ring end gap should be within the manufacturer’s specifications.
Cylinder Bore Diameter: Measure the cylinder bore diameter to check for wear.

Troubleshooting Cylinder and Piston Issues

Low Compression: This can be caused by worn piston rings, a damaged cylinder, or a leaky valve.
Reduced Power: This can be caused by worn piston rings, a damaged cylinder, or carbon buildup in the ports.
Excessive Smoke: This can be caused by worn piston rings allowing oil to enter the combustion chamber.

Real-World Example

I once worked on a Stihl MS291 that had been used extensively for commercial logging. The chainsaw had lost a significant amount of power and was difficult to start. I performed a compression test and found that the compression reading was only 90 PSI. I removed the cylinder head and found that the cylinder walls were heavily scored and the piston rings were worn. I replaced the cylinder and piston with new ones, and the chainsaw ran like new.

Takeaway

Regular inspection of the cylinder and piston is crucial for assessing the overall health of your chainsaw’s engine. By performing a compression test and visually inspecting the cylinder and piston, you can identify potential problems early and prevent costly repairs.

Maintaining Your MS291 for Longevity

Beyond these five key engine fixes, several other maintenance tasks will contribute to the longevity and performance of your Stihl MS291.

Chain and Bar Maintenance

A sharp chain and a well-maintained bar are essential for efficient cutting and safe operation.

Chain Sharpening: Sharpen the chain regularly using a chainsaw file or a chain grinder. A dull chain requires more force to cut, which can strain the engine and increase the risk of kickback. I prefer to sharpen my chain every time I refuel.
Bar Maintenance: Clean the bar regularly and check the bar rails for wear. File the bar rails if they are burred or uneven.
Chain Lubrication: Ensure the chain is properly lubricated with chainsaw bar oil. A lack of lubrication can cause the chain to overheat and wear out quickly.

Regular Cleaning

Keeping your chainsaw clean is essential for preventing dirt and debris from damaging the engine and other components.

External Cleaning: Clean the chainsaw regularly with a brush or cloth to remove dirt, sawdust, and oil.
Cooling Fins: Clean the cooling fins on the cylinder head to prevent overheating.
Muffler Cleaning: Clean the spark arrestor screen on the muffler to prevent exhaust restrictions.

Proper Storage

Proper storage is essential for protecting your chainsaw from damage when it is not in use.

Empty the Fuel Tank: Empty the fuel tank before storing the chainsaw for an extended period.
Clean the Chainsaw: Clean the chainsaw thoroughly before storing it.
Store in a Dry Place: Store the chainsaw in a dry, well-ventilated place to prevent rust and corrosion.
Chain Protection: Use a bar cover to protect the chain and prevent accidental cuts.

Safety First: Prioritizing Safe Chainsaw Operation

No guide on chainsaw maintenance would be complete without emphasizing safety. Chainsaws are powerful tools that can cause serious injury if not used properly.

Personal Protective Equipment (PPE): Always wear appropriate PPE, including safety glasses, hearing protection, gloves, chainsaw chaps, and steel-toed boots.
Proper Training: Receive proper training on chainsaw operation and safety procedures.
Safe Cutting Techniques: Use safe cutting techniques to avoid kickback and other hazards.
Awareness of Surroundings: Be aware of your surroundings and avoid cutting in hazardous conditions.
Regular Maintenance: Perform regular maintenance on your chainsaw to ensure it is in safe working condition.

Final Thoughts

Maintaining a Stihl MS291 chainsaw requires a proactive approach and a commitment to regular maintenance. By following these five pro engine fixes and incorporating them into your routine, you can ensure your chainsaw remains a reliable and efficient tool for years to come. Remember, a well-maintained chainsaw not only performs better but also operates more safely. So, take the time to care for your MS291, and it will reward you with years of dependable service. Now get out there and make some sawdust!