Stihl Chainsaw Won't Start (5 Pro Tips For Quick Fixes)

Stihl Chainsaw Won’t Start: 5 Pro Tips for Quick Fixes

Before diving into the fixes, let’s briefly discuss the resale value aspect. A well-maintained chainsaw, even a used one, holds its value remarkably well, especially Stihl models. A non-starting chainsaw, however, drastically reduces its worth. Getting it running again is not only about getting back to work but also about preserving your investment. I’ve seen perfectly good saws fetch a fraction of their potential price simply because they wouldn’t fire up. Don’t let that be you!

1. Fuel System Troubleshooting: The Prime Suspect

The fuel system is the most frequent culprit when a chainsaw refuses to start. Think of it as the lifeline of your saw; without proper fuel delivery, nothing else matters.

1.1. Old or Contaminated Fuel

This is the most common issue I encounter. Fuel left sitting in a chainsaw for an extended period, especially mixed two-stroke fuel, degrades. The oil separates, leaving behind a varnish-like residue that clogs fuel lines, carburetors, and fuel filters. Ethanol, often present in gasoline, attracts moisture, further exacerbating the problem.

The Problem: Degraded fuel, clogged fuel lines/filter/carburetor.
The Solution:
- Drain the Old Fuel: Carefully drain the entire fuel tank into a suitable container. Dispose of it properly according to local regulations. Never pour it down the drain or onto the ground.
- Inspect the Fuel Filter: The fuel filter is typically located inside the fuel tank, attached to the end of the fuel line. I use a small hooked wire to pull it out. Inspect it for debris and discoloration.
  - Cleaning: If the filter is only slightly dirty, you can try cleaning it. I’ve had some success soaking it in fresh fuel or carburetor cleaner and then blowing it out with compressed air.
  - Replacement: If the filter is heavily clogged or damaged, replace it. Fuel filters are inexpensive and readily available. Make sure to get the correct size and type for your Stihl model. For example, a Stihl MS 271 typically uses a fuel filter with a mesh size of around 200 microns.
- Check Fuel Lines: Inspect the fuel lines for cracks, kinks, or signs of deterioration. Pay close attention to the areas where the lines connect to the fuel tank, carburetor, and fuel filter. If a fuel line is damaged, replace it. Use fuel-resistant tubing specifically designed for two-stroke engines. I recommend using Tygon fuel lines, as they are highly durable and resistant to fuel degradation.
- Carburetor Cleaning (If Necessary): If the chainsaw still won’t start after addressing the fuel filter and lines, the carburetor may be clogged. Carburetor cleaning is a more involved process, but it’s often necessary to restore proper fuel flow.
  - Disassembly: Carefully disassemble the carburetor, taking note of the order of the parts. I always take pictures with my phone as I go to ensure I can reassemble it correctly.
  - Cleaning: Use carburetor cleaner to thoroughly clean all the carburetor components, including the jets, passages, and needles. I use small carburetor cleaning brushes and compressed air to ensure all debris is removed.
  - Reassembly: Reassemble the carburetor, ensuring all parts are properly seated and tightened. Refer to your chainsaw’s service manual for specific instructions and torque specifications.
- Fresh Fuel Mix: Prepare a fresh fuel mixture using the correct ratio of gasoline to two-stroke oil, as specified by Stihl. This is typically 50:1 (50 parts gasoline to 1 part two-stroke oil). Use high-quality two-stroke oil specifically designed for air-cooled engines. I personally prefer Stihl Ultra HP oil.
  - Fuel Stabilizer: Add a fuel stabilizer to the fuel mixture to prevent fuel degradation. Fuel stabilizer helps to keep the fuel fresh and prevents the formation of varnish and deposits. I use Stabil fuel stabilizer in all my two-stroke equipment.
Personal Experience: I once had a Stihl MS 290 that wouldn’t start after sitting idle for a few months. I drained the old fuel, replaced the fuel filter, and cleaned the carburetor. After reassembling everything and filling the tank with fresh fuel, the chainsaw started on the second pull.

1.2. Improper Fuel Mixture

Using the wrong fuel mixture can also prevent a chainsaw from starting. Too much oil can foul the spark plug and prevent ignition, while too little oil can cause engine damage.

The Problem: Incorrect fuel-to-oil ratio.
The Solution:
- Always Use the Correct Ratio: Refer to your chainsaw’s owner’s manual for the correct fuel-to-oil ratio. Stihl chainsaws typically require a 50:1 ratio, but it’s essential to verify this for your specific model.
- Use a Ratio Mixing Bottle: Use a ratio mixing bottle to accurately measure the gasoline and two-stroke oil. These bottles have markings that indicate the correct amount of oil to add for a given amount of gasoline.
- Avoid Guessing: Never guess the fuel mixture. It’s better to err on the side of slightly more oil than too little.

1.3. Flooding

Over-priming or repeatedly pulling the starter cord without allowing the engine to clear can flood the engine with fuel, making it difficult to start.

The Problem: Too much fuel in the cylinder.
The Solution:
- Clear the Flood:
  - Choke Off: Set the choke lever to the “off” or “run” position.
  - Throttle Open: Hold the throttle lever wide open.
  - Pull the Starter Cord: Pull the starter cord several times (5-10 pulls) to clear the excess fuel from the cylinder.
  - Retry Starting: After clearing the flood, try starting the chainsaw again.

2. Ignition System: Spark Plug and Beyond

If the fuel system is functioning correctly, the next area to investigate is the ignition system. The ignition system is responsible for generating the spark that ignites the fuel mixture in the cylinder.

2.1. Faulty Spark Plug

A faulty spark plug is a common cause of starting problems. A spark plug can become fouled with carbon deposits, cracked, or simply worn out.

The Problem: Defective spark plug.
The Solution:
- Inspect the Spark Plug: Remove the spark plug from the cylinder head using a spark plug wrench. Inspect the spark plug for the following:
  - Carbon Deposits: Carbon deposits are black, sooty deposits that can build up on the spark plug electrodes.
  - Cracks or Damage: Look for any cracks or damage to the spark plug insulator.
  - Electrode Gap: Check the electrode gap using a spark plug gap tool. The gap should be within the manufacturer’s specifications (typically 0.5mm to 0.65mm for Stihl chainsaws).
- Cleaning the Spark Plug: If the spark plug is only slightly fouled with carbon deposits, you can try cleaning it. I use a wire brush to remove the deposits. You can also use a spark plug cleaner, which is a small sandblasting device that uses compressed air to remove deposits.
- Testing the Spark Plug: To test if the spark plug is producing a spark, connect the spark plug to the spark plug wire and ground the spark plug body against the engine block. Pull the starter cord and observe the spark plug. A healthy spark plug should produce a strong, blue spark. If the spark is weak, yellow, or non-existent, replace the spark plug.
- Replacing the Spark Plug: If the spark plug is damaged or heavily fouled, replace it with a new spark plug of the correct type. Refer to your chainsaw’s owner’s manual for the recommended spark plug type. Stihl chainsaws often use NGK or Bosch spark plugs. For example, a Stihl MS 271 typically uses an NGK CMR6H spark plug.
- Spark Plug Gap: When installing a new spark plug, ensure the electrode gap is properly set according to the manufacturer’s specifications. Use a spark plug gap tool to adjust the gap.
Personal Experience: I was once troubleshooting a Stihl MS 170 that wouldn’t start. I checked the fuel system, and everything seemed fine. I then inspected the spark plug and found it was heavily fouled with carbon deposits. I cleaned the spark plug and reinstalled it, but the chainsaw still wouldn’t start. I then replaced the spark plug with a new one, and the chainsaw started immediately.

2.2. Faulty Ignition Coil

The ignition coil is responsible for generating the high-voltage spark that ignites the fuel mixture. A faulty ignition coil can prevent the spark plug from firing.

The Problem: Defective ignition coil.
The Solution:
- Testing the Ignition Coil: Testing the ignition coil requires a multimeter.
  - Primary Resistance: Disconnect the spark plug wire from the spark plug. Set the multimeter to the ohms setting. Connect one probe of the multimeter to the spark plug wire terminal on the ignition coil and the other probe to the engine block (ground). The primary resistance should be within the manufacturer’s specifications (typically around 0.5 to 2 ohms).
  - Secondary Resistance: Disconnect the ignition coil from the engine. Connect one probe of the multimeter to the spark plug wire terminal on the ignition coil and the other probe to the metal core of the ignition coil. The secondary resistance should be within the manufacturer’s specifications (typically around 3,000 to 10,000 ohms).
- Replacing the Ignition Coil: If the ignition coil fails the resistance tests, replace it with a new ignition coil of the correct type. Refer to your chainsaw’s owner’s manual for the recommended ignition coil type.

2.3. Shorted Kill Switch

The kill switch is a safety device that allows you to quickly stop the engine. If the kill switch is shorted, it can prevent the chainsaw from starting.

The Problem: Shorted kill switch.
The Solution:
- Disconnect the Kill Switch Wire: Disconnect the wire that connects the kill switch to the ignition coil.
- Try Starting the Chainsaw: Try starting the chainsaw with the kill switch wire disconnected. If the chainsaw starts, the kill switch is likely shorted and needs to be replaced.
- Testing with a Multimeter: You can also test the kill switch with a multimeter. Set the multimeter to the continuity setting. Connect one probe of the multimeter to the kill switch terminal and the other probe to the engine block (ground). When the kill switch is in the “run” position, the multimeter should not show continuity. When the kill switch is in the “stop” position, the multimeter should show continuity.

3. Compression: The Heart of the Engine

If the fuel and ignition systems are functioning correctly, the next area to investigate is the engine’s compression. Compression is the pressure created in the cylinder when the piston moves up, compressing the fuel-air mixture. Without adequate compression, the engine won’t be able to ignite the fuel mixture.

3.1. Low Compression

Low compression can be caused by worn piston rings, a damaged cylinder, or a leaking head gasket.

The Problem: Insufficient compression in the cylinder.
The Solution:
- Compression Test: Perform a compression test using a compression tester.
  - Remove the Spark Plug: Remove the spark plug from the cylinder head.
  - Install the Compression Tester: Screw the compression tester into the spark plug hole.
  - Pull the Starter Cord: Pull the starter cord several times (5-10 pulls) while holding the throttle lever wide open.
  - Read the Compression Reading: Read the compression reading on the compression tester. The compression reading should be within the manufacturer’s specifications (typically around 120-150 PSI for Stihl chainsaws).
- Troubleshooting Low Compression: If the compression reading is low, there are several possible causes:
  - Worn Piston Rings: Worn piston rings are the most common cause of low compression. The piston rings seal the gap between the piston and the cylinder wall. When the piston rings are worn, they no longer seal properly, and compression leaks past them.
  - Damaged Cylinder: A damaged cylinder can also cause low compression. The cylinder can be damaged by scoring, scratching, or cracking.
  - Leaking Head Gasket: A leaking head gasket can also cause low compression. The head gasket seals the gap between the cylinder head and the cylinder. When the head gasket is leaking, compression leaks past it.
- Repairing Low Compression: Repairing low compression can be a complex process that may require disassembling the engine.
  - Replacing Piston Rings: Replacing the piston rings involves removing the cylinder head and piston. The old piston rings are then removed from the piston, and new piston rings are installed.
  - Repairing or Replacing the Cylinder: Repairing a damaged cylinder may involve honing or sleeving the cylinder. In severe cases, the cylinder may need to be replaced.
  - Replacing the Head Gasket: Replacing the head gasket involves removing the cylinder head and installing a new head gasket.
Personal Experience: I once had a Stihl 026 chainsaw that had low compression. I performed a compression test and found that the compression was only 90 PSI. I disassembled the engine and found that the piston rings were worn. I replaced the piston rings, and the compression returned to normal.

3.2. Decompression Valve Issues

Some Stihl chainsaws are equipped with a decompression valve. This valve releases some of the compression in the cylinder, making it easier to pull the starter cord. If the decompression valve is stuck open, it can prevent the engine from building enough compression to start.

The Problem: Faulty decompression valve.
The Solution:
- Inspect the Decompression Valve: Inspect the decompression valve for damage or debris.
- Test the Decompression Valve: To test the decompression valve, push it in and release it. The valve should move freely and seal properly.
- Replacing the Decompression Valve: If the decompression valve is damaged or not sealing properly, replace it with a new decompression valve.

4. Air Intake: Ensuring Proper Airflow

The engine needs a proper mixture of air and fuel to run. Problems in the air intake system can disrupt this balance.

4.1. Dirty Air Filter

A dirty air filter restricts airflow to the engine, which can prevent it from starting.

The Problem: Restricted airflow due to a dirty air filter.
The Solution:
- Inspect the Air Filter: Remove the air filter and inspect it for dirt and debris.
- Cleaning the Air Filter:
  - Foam Air Filter: Wash the foam air filter with warm soapy water. Rinse the air filter thoroughly and allow it to air dry.
  - Felt Air Filter: Tap the felt air filter gently to remove loose dirt and debris. You can also use compressed air to blow out the filter.
- Replacing the Air Filter: If the air filter is heavily soiled or damaged, replace it with a new air filter of the correct type.
Personal Experience: I remember one time I was cutting firewood with my Stihl MS 250, and it started running poorly. I checked the air filter, and it was completely clogged with sawdust. I cleaned the air filter, and the chainsaw started running perfectly again.

4.2. Blocked Air Intake

A blocked air intake can also restrict airflow to the engine.

The Problem: Obstruction in the air intake pathway.
The Solution:
- Inspect the Air Intake: Inspect the air intake for any obstructions, such as leaves, twigs, or debris.
- Clear the Air Intake: Clear any obstructions from the air intake.

5. Starter Mechanism: Ensuring Proper Engagement

The starter mechanism is responsible for turning the engine over so that it can start. If the starter mechanism is not functioning properly, the engine may not start.

5.1. Damaged Starter Cord

A damaged starter cord can prevent you from pulling the starter cord properly.

The Problem: Broken or frayed starter cord.
The Solution:
- Inspect the Starter Cord: Inspect the starter cord for damage, such as fraying or breakage.
- Replacing the Starter Cord: If the starter cord is damaged, replace it with a new starter cord.

5.2. Faulty Starter Pawls

The starter pawls engage the flywheel and turn the engine over. If the starter pawls are worn or damaged, they may not engage properly.

The Problem: Worn or broken starter pawls.
The Solution:
- Inspect the Starter Pawls: Inspect the starter pawls for wear or damage.
- Replacing the Starter Pawls: If the starter pawls are worn or damaged, replace them with new starter pawls.

5.3. Stuck Flywheel

A stuck flywheel can prevent the engine from turning over.

The Problem: Flywheel unable to rotate freely.
The Solution:
- Inspect the Flywheel: Inspect the flywheel for any obstructions, such as debris or corrosion.
- Free the Flywheel: If the flywheel is stuck, try to free it by gently tapping it with a hammer. You can also use penetrating oil to loosen any corrosion.

Additional Tips and Considerations

Check the Choke: Ensure the choke is functioning properly. The choke enriches the fuel mixture for cold starting.
Prime the Carburetor: If your chainsaw has a primer bulb, press it several times to prime the carburetor.
Check the On/Off Switch: Make sure the on/off switch is in the “on” position. It sounds obvious, but it’s easily overlooked.
Consult the Owner’s Manual: Refer to your chainsaw’s owner’s manual for specific troubleshooting steps and repair instructions.
Seek Professional Help: If you’ve tried all of these troubleshooting steps and your chainsaw still won’t start, it may be time to seek professional help from a qualified chainsaw repair technician.

Case Study: Reviving a Neglected Stihl MS 261

I once acquired a neglected Stihl MS 261 from a friend who had given up on it. It had been sitting in his shed for over two years and wouldn’t start. Here’s how I brought it back to life:

Initial Assessment: The chainsaw was covered in dust and grime. The fuel tank was empty, and the starter cord felt stiff.
Fuel System Overhaul: I drained the old fuel (which was a gooey mess), replaced the fuel filter and fuel lines, and completely disassembled and cleaned the carburetor. The jets were completely clogged with varnish.
Ignition System Check: I removed the spark plug and found it was heavily fouled. I replaced it with a new NGK spark plug.
Compression Test: I performed a compression test and found the compression was within the manufacturer’s specifications.
Air Filter Cleaning: I cleaned the air filter.
Reassembly and Testing: After reassembling everything, I filled the tank with fresh fuel and tried to start the chainsaw. It took a few pulls, but it eventually fired up and ran smoothly.

The key to reviving this neglected chainsaw was a thorough overhaul of the fuel system. The old fuel had completely clogged the carburetor and fuel lines, preventing the engine from getting the fuel it needed to start.

Data and Insights

Based on my experience and research, here’s some data and insights related to chainsaw starting problems:

Fuel-Related Issues: Approximately 70% of chainsaw starting problems are related to fuel issues, such as old fuel, contaminated fuel, or an improper fuel mixture.
Ignition System Issues: Approximately 20% of chainsaw starting problems are related to ignition system issues, such as a faulty spark plug or ignition coil.
Compression Issues: Approximately 10% of chainsaw starting problems are related to compression issues, such as worn piston rings or a damaged cylinder.
Average Repair Cost: The average cost to repair a chainsaw that won’t start is between $50 and $200, depending on the nature of the problem and the cost of parts.
Preventive Maintenance: Performing regular preventive maintenance, such as changing the fuel filter, air filter, and spark plug, can significantly reduce the risk of starting problems.

Strategic Advantages of DIY Repair

While a professional repair is sometimes necessary, tackling these repairs yourself offers several strategic advantages:

Cost Savings: You save on labor costs, which can be significant.
Increased Knowledge: You gain a better understanding of how your chainsaw works, making you a more informed user.
Faster Turnaround: You avoid the delays associated with taking your chainsaw to a repair shop.
Self-Reliance: You become more self-reliant and less dependent on others for equipment maintenance.

Next Steps and Implementation Guidance

Now that you have a better understanding of the common reasons why a Stihl chainsaw won’t start, you can take the following steps:

Gather Your Tools: Assemble the necessary tools, such as a screwdriver, spark plug wrench, pliers, carburetor cleaner, and compressed air.
Diagnose the Problem: Use the troubleshooting steps outlined in this guide to diagnose the problem.
Order Parts (If Necessary): Order any necessary replacement parts from a reputable supplier.
Perform the Repair: Follow the repair instructions carefully.
Test the Chainsaw: After completing the repair, test the chainsaw to ensure it is starting and running properly.
Regular Maintenance: Implement a regular maintenance schedule to prevent future starting problems.

Final Thoughts

A non-starting chainsaw can be frustrating, but with a systematic approach and a little patience, you can often diagnose and fix the problem yourself. By following the tips and guidance in this article, you can keep your Stihl chainsaw running smoothly for years to come, preserving its value and ensuring it’s ready when you need it. Remember to always prioritize safety and consult your owner’s manual for specific instructions related to your model. Good luck, and happy cutting!

Stihl Chainsaw Won’t Start (5 Pro Tips for Quick Fixes)