Stihl MS170 Won’t Start: Troubleshooting and Solutions

Stihl MS170 Won't Start: Troubleshooting and Solutions

I recently struggled to get my Stihl MS170 chainsaw started, which was incredibly frustrating. As an avid DIYer who relies on my tools, having an out-of-commission chainsaw was a real problem. After some troubleshooting and research, I was able to get my saw running again. Based on my experience, I wanted to provide a comprehensive guide to troubleshooting and solving starting problems with the Stihl MS170 chainsaw.

Proper maintenance and troubleshooting are critical for keeping your chainsaw in good working order. In this article, I’ll cover the most common reasons why your Stihl chainsaw won’t start and provide solutions to get it up and running again. Whether it’s fuel system issues, spark plug problems, clutch malfunctions, or something else entirely, this guide will help you reliably diagnose and repair your balky chainsaw.

Stihl MS170 Won’t Start: What Could Be the Problem?

Stihl MS170 Won't Start: Troubleshooting and Solutions

When your Stihl chainsaw won’t start, there are a number of potential culprits to investigate. Here are some of the most common issues that can prevent your saw from starting properly:

Fuel Issues

One of the first things to check when your Stihl MS170 won’t start is the fuel system. Using the proper fuel mix is critical – you should always use a 50:1 ratio of gas to 2-stroke engine oil. Old gas that has been sitting for too long can cause starting issues, so always use fresh fuel. Verify that your fuel tank has enough gas and inspect the fuel line for any blockages or leaks. Replacing deteriorated fuel lines and filters can often resolve starting problems. Make sure to regularly inspect and maintain the carburetor as well.

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Carburetor Problems

A clogged or malfunctioning carburetor is another prime suspect when diagnosing starting issues. Remove the air filter and carburetor to inspect for dirt, debris or corrosion that could be blocking fuel flow. Carefully clean the carburetor passages and components with carburetor cleaner. Inspect the gaskets and diaphragms for any cracks or damage. Adjusting the carburetor may help improve performance. If cleaning doesn’t solve the issue, rebuilding or replacing the carburetor may be necessary.

Spark Plug Issues

Without adequate spark, your chainsaw engine can’t ignite the fuel mixture. Examine the spark plug – if it’s fouled or damaged, replace it with a new one. Make sure the spark plug gap is properly set. Verify that the spark plug boot and wire are intact and connected. Checking for spark by grounding the plug against the engine can confirm if ignition is the problem. Regularly changing the spark plug is wise preventive maintenance.

Air Filter Problems

A dirty, clogged air filter starves the engine of air, making starting difficult. Check the air filter to see if it’s covered in debris – a blocked filter prevents proper air intake. Gently clean the air filter with soap and water if it’s dirty, or replace it if excessively clogged. Make sure to reinstall the air filter properly. Check that the choke is opening and closing smoothly as well.

Clutch Issues

The centrifugal clutch engages the chain drive when the chainsaw engine reaches a sufficient speed. If the clutch is sticking or slipping, it could prevent the saw from starting. Examine the clutch for any broken springs or worn parts. Refer to your owner’s manual for specifics on inspecting and replacing clutch components. Seek professional repair assistance if needed.

Vapor Lock

Vapor lock occurs when heat makes fuel vapors form bubbles in the fuel system, blocking proper fuel flow. This can prevent starting, cause stalling, or make restarting difficult after use. Allow the chainsaw to fully cool before attempting to restart. Store your saw in a shady area. Installing an aftermarket fuel line kit designed to reduce vapor lock can help.

Overheated Air Filter

Running your chainsaw in extremely dusty conditions can cause the air filter to become overheated. This heat transfer can make restarting difficult. Avoid excessive air filter temperatures by cleaning the filter regularly. Check that the filter and area around the carburetor are free of dirt buildup. Allow your saw to completely cool down before attempting to restart after significant overheating.

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Stihl Chainsaw Not Oiling Bar

In addition to starting trouble, inadequate oiling of the guide bar is another common problem with Stihl chainsaws. Without proper lubrication, the chain and bar will quickly wear out. Check the oil tank level and fill up if low. Inspect the oil delivery holes in the bar for blockages. Clean out the oil passages in the bar and verify the oil pump is working correctly. Replace worn bar oil adjustment screws if the pump isn’t metering oil properly. Use only high-quality bar and chain oil specifically formulated for chainsaws.

Proper Starting Procedure for Stihl MS170

Following the correct starting procedure is crucial to getting your Stihl chainsaw running reliably. Here are the proper steps to start the MS170:

  1. Move the master control lever to the cold start position.
  2. Press the primer bulb 6 times to prime the carburetor.
  3. Pull out the choke knob to close the choke valve.
  4. Firmly pull the starter cord 5-6 times to crank the engine.
  5. Push the choke knob back in to open the choke valve.
  6. Pull the starter cord sharply until the engine starts.
  7. Allow the engine to warm up for several minutes before using.

Carefully following this sequence prevents flooding and helps start the saw. Always avoid cranking the starter excessively to prevent spark plug fouling.

Regular Maintenance and Cleaning

Performing regular maintenance and cleaning is the best way to prevent starting issues and keep your Stihl MS170 running optimally. Here are some key maintenance tips:

  • Clean the air filter regularly and replace when worn.
  • Change the spark plug annually.
  • Inspect the clutch and fuel system for wear.
  • Sharpen or replace the chain when dull.
  • Use fresh fuel with the proper 50:1 gas/oil mix.
  • Clear debris from the starter housing and chain brake.
  • Check all screws/bolts and tighten if loose.

Also be sure to wipe down your saw after each use to prevent dirt, sap, and sawdust buildup. Store the chainsaw properly in a clean, dry location. Performing maintenance as recommended in the owner’s manual will keep your saw starting reliably for years to come.

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When to Seek Professional Help

While this guide covers many common issues, there are times when it’s best to seek assistance from a professional technician:

  • If you’ve checked all potential issues listed but the saw still won’t start.
  • If the saw won’t start after replacing major components like the carburetor.
  • If you notice any severe damage or wear on critical engine parts.
  • If you lack the knowledge, skill, or tools to safely troubleshoot and repair the chainsaw.

Seeking professional repair from an authorized Stihl dealer is advisable if you are unable to diagnose and fix the starting issues on your own. Trained Stihl technicians have the expertise to get your troublesome chainsaw running again quickly.


I hope this guide provides useful troubleshooting tips to get your balky Stihl MS170 chainsaw starting again. Proper maintenance and care is crucial for keeping your saw in good working order. Always use fresh fuel, clean the air filter regularly, change the spark plug annually, and follow the correct starting procedures. Seek professional assistance if needed. With some diligent troubleshooting and diagnostic work, you can identify and fix the problem and get back to cutting wood efficiently.

Frequently Asked Questions

What is the correct fuel mix for a Stihl MS170 chainsaw?

The proper fuel mix is 50:1, or 50 parts gasoline to 1 part 2-stroke engine oil. Always use fresh fuel less than 30 days old.

How often should I clean the air filter on my Stihl MS170?

Clean the air filter every 5 hours of use or more frequently if working in very dusty conditions. Replace the filter if it becomes excessively dirty or damaged.

Can I use any brand of bar oil for my Stihl MS170 chainsaw?

No, you should use only Stihl bar and chain oil or another oil made specifically for chainsaw bar lubrication. Regular motor oil can cause damage.

How do I adjust the carburetor on my Stihl MS170 chainsaw?

The carburetor is preset at the factory and adjustment is not normally needed. Consult your owner’s manual or a dealer if adjustment is required.

What should I do if my Stihl MS170 chainsaw is overheating?

Allow the saw to completely cool before restarting. Clean dirt and debris from the engine and air filter. DO NOT modify the engine speed. Seek repair if overheating continues.

How can I prevent vapor lock in my Stihl MS170 chainsaw?

Keep the saw cooled and in the shade when not in use. Install an aftermarket fuel line kit for hot weather. Allow the engine to cool before restarting after use.

How often should I replace the spark plug on my Stihl MS170 chainsaw?

The spark plug should be replaced yearly or after 100 hours of runtime. Check that the gap is properly set to 0.020 inches (0.5mm).

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