Stihl MS171 Troubleshooting Tips (5 Expert Fixes You Must Know)

The Stihl MS 171 is a workhorse, a reliable companion for countless homeowners and occasional users tackling everything from trimming branches to felling small trees. But even the most dependable machines can stumble. When your MS 171 sputters, stalls, or refuses to start, it’s frustrating. I’ve been there, wrench in hand, trying to coax life back into a silent saw. Over the years, I’ve learned that most issues stem from a handful of common culprits. This guide isn’t just a list of fixes; it’s a culmination of my experience, offering practical, actionable solutions to get your Stihl MS 171 roaring back to life.

Stihl MS 171 Troubleshooting Tips (5 Expert Fixes You Must Know)

Understanding the Stihl MS 171: A Foundation for Troubleshooting

Before diving into specific fixes, let’s establish a basic understanding of how the Stihl MS 171 operates. This compact chainsaw features a two-stroke engine, meaning it requires a precise mixture of gasoline and oil for lubrication. The carburetor regulates the fuel-air mixture, while the ignition system provides the spark to ignite it. Understanding this interplay is crucial for diagnosing problems.

Key Components and Their Functions:

• Fuel Tank: Holds the gasoline and oil mixture (typically a 50:1 ratio for the MS 171).
• Fuel Filter: Prevents debris from entering the fuel line and carburetor.
• Fuel Line: Delivers fuel from the tank to the carburetor.
• Carburetor: Mixes fuel and air in the correct proportion for combustion.
• Air Filter: Prevents dust and debris from entering the engine.
• Spark Plug: Provides the spark to ignite the fuel-air mixture.
• Ignition Module: Generates the high-voltage electricity for the spark plug.
• Muffler: Reduces engine noise and directs exhaust gases away from the operator.

Why This Matters for Troubleshooting:

Knowing the function of each component allows you to logically narrow down potential problems. For instance, if the engine isn’t getting fuel, you’ll focus on the fuel tank, filter, line, and carburetor.

My Experience:

I recall a time when my MS 171 refused to start after sitting idle for a few months. I initially suspected a major engine issue. However, after systematically checking each component, I discovered a clogged fuel filter. A simple replacement solved the problem, highlighting the importance of starting with the basics.

Takeaway:

Familiarize yourself with the key components of your Stihl MS 171. This knowledge will be invaluable when diagnosing and resolving issues.

Fix #1: The Fuel System Fiasco: Addressing Fuel Delivery Problems

Fuel-related issues are among the most common causes of starting and running problems in the MS 171. From stale fuel to clogged filters, several factors can disrupt the fuel delivery system.

Symptoms:

• Engine won’t start.
• Engine starts but stalls quickly.
• Engine runs poorly with a lack of power.
• Engine surges or hesitates.

Possible Causes and Solutions:

1. Stale Fuel: Gasoline degrades over time, especially when mixed with oil. This can lead to poor combustion and starting problems.

   • Solution: Drain the old fuel completely and replace it with fresh fuel mixed with the correct ratio of two-stroke oil (50:1). I recommend using a fuel stabilizer if you plan to store the saw for an extended period.

   • Clogged Fuel Filter: The fuel filter prevents debris from entering the fuel line and carburetor. A clogged filter restricts fuel flow.

   • Solution: Locate the fuel filter inside the fuel tank (it’s usually attached to the end of the fuel line). Carefully remove it and inspect for debris. If clogged, replace it with a new filter. Fuel filters are inexpensive and readily available. I always keep a spare on hand.

   • Blocked Fuel Line: A kinked or cracked fuel line can restrict fuel flow.

   • Solution: Inspect the fuel line for any visible damage. If you find a kink or crack, replace the fuel line. Pay attention to the routing of the fuel line to avoid future kinks.

   • Carburetor Issues: The carburetor mixes fuel and air. A dirty or improperly adjusted carburetor can cause a variety of problems.

   • Solution: Start by cleaning the carburetor. You can use carburetor cleaner spray to remove deposits. If the carburetor is severely clogged, you may need to disassemble it and clean each component individually. Refer to the Stihl MS 171 service manual for detailed instructions. Carburetor adjustment can be tricky. If you’re not comfortable with it, I recommend taking the saw to a qualified technician. The MS 171 usually only has one adjustment screw, the LA (Low Adjustment). Turning it clockwise leans the mixture, counter-clockwise enriches it. Adjust in small increments.

   • Ventilation Problems: Fuel tanks need to be properly ventilated to allow fuel to flow freely. A clogged vent can create a vacuum in the tank, preventing fuel from reaching the carburetor.

   • Solution: Locate the fuel tank vent (usually a small hole or valve on the fuel tank cap or near the carburetor). Clean it with a small wire or compressed air to ensure it’s clear.

Real-World Example:

I once spent hours troubleshooting a MS 171 that wouldn’t start. I checked the spark plug, the air filter, and even started suspecting the ignition module. Finally, out of desperation, I checked the fuel tank vent. It was completely clogged with sawdust. After cleaning it, the saw started on the first pull.

Tool List:

• Screwdriver (for removing fuel filter and accessing fuel lines)
• Pliers (for removing and installing fuel lines)
• Carburetor cleaner spray
• Compressed air (optional)
• New fuel filter
• New fuel line (if needed)
• Fresh fuel and two-stroke oil

Metrics:

• Fuel mixture ratio: 50:1 (gasoline to two-stroke oil)
• Fuel filter replacement frequency: Every 50 hours of use or annually (whichever comes first)

Takeaway:

A clean and properly functioning fuel system is essential for the Stihl MS 171 to run smoothly. Regularly inspect and maintain the fuel filter, fuel lines, and carburetor to prevent problems.

Fix #2: The Air Intake Anomaly: Ensuring Proper Airflow

Just as fuel is critical, so is air. The engine needs a clean and unobstructed supply of air for proper combustion. A clogged air filter or blocked air intake can significantly impact performance.

Symptoms:

• Engine lacks power.
• Engine runs rough or stalls.
• Excessive smoke from the exhaust.
• Difficulty starting.

Possible Causes and Solutions:

1. Clogged Air Filter: The air filter prevents dust and debris from entering the engine. A dirty filter restricts airflow.

   • Solution: Remove the air filter and inspect it. If it’s dirty, clean it with warm soapy water. Allow the filter to dry completely before reinstalling it. If the filter is damaged or excessively dirty, replace it. I prefer foam filters, as they can be cleaned and reused multiple times.

   • Blocked Air Intake: Debris can accumulate around the air intake, restricting airflow.

   • Solution: Inspect the area around the air intake for any obstructions. Remove any debris, such as sawdust, leaves, or dirt.

   • Choke Problems: The choke restricts airflow to enrich the fuel mixture for starting a cold engine. If the choke is stuck in the closed position, it can cause the engine to flood.

   • Solution: Ensure the choke lever is in the correct position (open after starting). Check the choke linkage for any binding or damage.

My Experience:

I once had a MS 171 that would start but immediately stall. I checked everything I could think of – fuel, spark, compression. Finally, I realized that the air filter was so clogged with fine sawdust that it was completely blocking airflow. A quick cleaning solved the problem.

Tool List:

• Screwdriver (for removing air filter cover)
• Warm soapy water
• New air filter (if needed)
• Brush (for cleaning air filter)

Metrics:

• Air filter cleaning frequency: Every 10 hours of use or more frequently in dusty conditions.
• Air filter replacement frequency: Annually or as needed.

Takeaway:

Maintaining a clean air filter is crucial for optimal engine performance. Regularly inspect and clean the air filter to prevent airflow restrictions.

Fix #3: Ignition System Investigations: Spark Plug and Beyond

The ignition system is responsible for creating the spark that ignites the fuel-air mixture. A faulty spark plug or ignition module can prevent the engine from starting or running properly.

Symptoms:

• Engine won’t start.
• Weak or intermittent spark.
• Engine misfires.

Possible Causes and Solutions:

1. Faulty Spark Plug: A dirty, worn, or improperly gapped spark plug can prevent the engine from starting.

   • Solution: Remove the spark plug and inspect it. Look for signs of fouling (carbon buildup), damage, or excessive wear. Clean the spark plug with a wire brush or replace it with a new one. Ensure the spark plug gap is correct (typically 0.5 mm or 0.020 inches for the MS 171). Use a spark plug gapping tool to adjust the gap. I always keep a spare spark plug in my toolkit.

   • Weak Spark: A weak spark can be caused by a faulty ignition module or a loose connection.

   • Solution: Use a spark tester to check the spark. If the spark is weak or nonexistent, check the spark plug wire and connections. Ensure the spark plug wire is securely attached to the spark plug and the ignition module. If the connections are good, the ignition module may be faulty and need to be replaced. This is often best left to a qualified technician.

   • Ignition Module Problems: The ignition module generates the high-voltage electricity for the spark plug. A faulty ignition module can prevent the engine from starting.

   • Solution: Testing an ignition module requires specialized equipment. If you suspect a faulty ignition module, I recommend taking the saw to a qualified technician for diagnosis and repair.

Personal Story:

I once had a MS 171 that would start intermittently. Sometimes it would run fine, other times it would refuse to start. I suspected a fuel problem, but after checking everything, I realized the spark was weak and inconsistent. Replacing the spark plug solved the problem. It turned out the old spark plug was internally cracked, causing intermittent sparking.

Tool List:

• Spark plug wrench
• Spark plug gapping tool
• Wire brush
• Spark tester (optional)
• New spark plug

Metrics:

• Spark plug gap: 0.5 mm (0.020 inches)
• Spark plug replacement frequency: Annually or as needed.

Takeaway:

A strong and consistent spark is essential for the Stihl MS 171 to start and run properly. Regularly inspect and maintain the spark plug and ignition system.

Fix #4: Compression Checks and Cylinder Condition

While less frequent than fuel or ignition issues, compression problems can plague a Stihl MS 171. Low compression indicates wear or damage within the cylinder, impacting the engine’s ability to generate power.

Symptoms:

• Engine is difficult to start.
• Engine lacks power.
• Engine stalls easily.
• Unusual noises from the engine.

Possible Causes and Solutions:

1. Worn Piston Rings: Piston rings seal the combustion chamber and prevent gases from escaping. Over time, they can wear down, reducing compression.

   • Solution: A compression test can determine if the piston rings are worn. Use a compression tester to measure the cylinder pressure. A healthy MS 171 should have a compression reading of at least 120 PSI. If the compression is low, the piston rings may need to be replaced. This is a more complex repair that requires disassembling the engine. I recommend consulting a qualified technician.

   • Cylinder Damage: Scratches or damage to the cylinder wall can also reduce compression.

   • Solution: Inspect the cylinder wall for any visible damage. This usually requires removing the cylinder head. If the cylinder is damaged, it may need to be honed or replaced. Again, this is a complex repair best left to professionals.

   • Loose Cylinder Head Bolts: Loose cylinder head bolts can cause a loss of compression.

   • Solution: Check the cylinder head bolts to ensure they are properly tightened. Refer to the Stihl MS 171 service manual for the correct torque specifications.

   • Damaged Cylinder Gasket: A damaged cylinder gasket can leak compression.

   • Solution: Inspect the cylinder gasket for any signs of damage. If the gasket is damaged, it needs to be replaced.

A Cautionary Tale:

I once inherited a MS 171 that had been neglected for years. It was extremely difficult to start and lacked power. A compression test revealed very low compression. Upon disassembly, I discovered that the piston rings were completely worn and the cylinder wall had several deep scratches. The engine was essentially beyond repair. This experience taught me the importance of regular maintenance and proper lubrication.

Tool List:

• Compression tester
• Wrench (for cylinder head bolts)
• Screwdriver (for removing cylinder head)
• New cylinder gasket (if needed)
• Torque wrench

Metrics:

• Minimum acceptable compression: 120 PSI

Takeaway:

Maintaining proper lubrication and avoiding overheating can help prevent compression problems. If you suspect a compression issue, perform a compression test to diagnose the problem.

Fix #5: The Carburetor Conundrum: Deep Dive into Carburetor Issues

I touched on carburetor issues earlier, but the carburetor is such a critical component that it deserves a more in-depth look. Carburetor problems are a common cause of running issues in the MS 171.

Symptoms:

• Engine won’t start.
• Engine starts but stalls quickly.
• Engine runs poorly with a lack of power.
• Engine surges or hesitates.
• Engine idles erratically.

Possible Causes and Solutions:

1. Dirty Carburetor: Deposits and debris can accumulate in the carburetor, clogging jets and passages.

   • Solution: Remove the carburetor and clean it thoroughly with carburetor cleaner spray. Pay particular attention to the jets and passages. Use a small wire or carburetor cleaning tool to clear any blockages. I recommend soaking the carburetor in carburetor cleaner for several hours to dissolve stubborn deposits.

   • Incorrect Carburetor Adjustment: The carburetor needs to be properly adjusted to provide the correct fuel-air mixture.

   • Solution: The MS 171 typically only has one adjustment screw, the LA (Low Adjustment), used to adjust the idle speed and low-speed fuel mixture. Refer to the Stihl MS 171 service manual for the correct adjustment procedure. A tachometer can be helpful for setting the correct idle speed. Turn the LA screw until the engine idles smoothly without stalling. Adjust in small increments.

   • Damaged Carburetor Components: Worn or damaged carburetor components, such as diaphragms and needles, can cause problems.

   • Solution: Inspect the carburetor components for any signs of damage. If you find any damaged components, replace them. Carburetor rebuild kits are available and include all the necessary parts.

   • Air Leaks: Air leaks around the carburetor can disrupt the fuel-air mixture.

   • Solution: Inspect the carburetor mounting flange and intake manifold for any signs of air leaks. Use carburetor cleaner spray to check for leaks. Spray the cleaner around the carburetor while the engine is running. If the engine speed changes, there is likely an air leak. Tighten the carburetor mounting bolts or replace the intake manifold gasket.

My Carburetor Cleaning Ritual:

When cleaning a carburetor, I follow a specific process:

1. Disassembly: Carefully disassemble the carburetor, taking note of the location of each component.
2. Cleaning: Soak all the metal parts in carburetor cleaner for several hours. Use a small brush and carburetor cleaning tool to remove any deposits.
3. Rinsing: Rinse all the parts with clean carburetor cleaner.
4. Drying: Dry all the parts with compressed air.
5. Reassembly: Reassemble the carburetor, ensuring all the components are in the correct location.
6. Adjustment: Adjust the carburetor according to the manufacturer’s specifications.

Tool List:

• Screwdriver
• Carburetor cleaner spray
• Carburetor cleaning tool
• Compressed air
• Carburetor rebuild kit (if needed)
• Tachometer (optional)

Metrics:

• Idle speed: Refer to the Stihl MS 171 service manual for the correct idle speed.
• Carburetor cleaning frequency: As needed, depending on fuel quality and usage.

Takeaway:

A clean and properly adjusted carburetor is essential for the Stihl MS 171 to run smoothly. Regularly clean and maintain the carburetor to prevent problems.

Additional Tips and Tricks for Stihl MS 171 Maintenance

Beyond the five key fixes, here are some additional tips and tricks to keep your Stihl MS 171 running in top condition:

• Use High-Quality Fuel and Oil: Always use fresh, high-quality gasoline and two-stroke oil. Avoid using fuel that has been stored for an extended period.
• Proper Storage: When storing the saw for an extended period, drain the fuel tank and run the engine until it stalls to remove any remaining fuel from the carburetor. This prevents fuel deposits from forming.
• Chain Maintenance: Keep the chain sharp and properly tensioned. A dull chain puts extra strain on the engine and can reduce cutting performance.
• Bar Lubrication: Ensure the chain and bar are properly lubricated. Use a high-quality bar and chain oil.
• Regular Inspections: Regularly inspect the saw for any signs of damage or wear. Check the fuel lines, air filter, spark plug, and other components.
• Refer to the Service Manual: The Stihl MS 171 service manual contains valuable information on maintenance and repair procedures.

Safety First:

Always wear appropriate safety gear when operating or maintaining a chainsaw, including:

• Eye protection
• Hearing protection
• Gloves
• Chaps
• Steel-toed boots

Final Thoughts:

Troubleshooting a Stihl MS 171 can seem daunting, but by understanding the basic principles of engine operation and following these expert fixes, you can diagnose and resolve most common problems. Remember to start with the basics, be methodical, and don’t hesitate to consult a qualified technician if you’re unsure about any repair. With proper maintenance and care, your Stihl MS 171 will provide years of reliable service. I hope these tips help you get your saw back in action and keep it running smoothly for years to come!

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