13 Most Common Stihl MS 391 Problems & Solutions

The STIHL MS 391 is a gasoline-powered chainsaw popular for home and professional use. It is a robust, powerful tool designed to tackle everyday tasks.

 However, specific issues can arise from using this chainsaw.

These problems can range from air filter blockages to spark plug faults. Make sure you’re aware of these issues and how they may affect the performance of your STIHL chainsaw.

 This blog post will cover some of the most common issues with the Stihl MS 391 and provide an overview of how you can troubleshoot each issue. 

The Most Common Problems with Stihl MS 391

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The Stihl MS 391 is a great chainsaw for homeowners, but it does have its share of problems; even the most reliable machines can experience problems from time to time.

This paragraph will discuss some of the most common Stihl MS 391 problems and solutions.

1. Hard Starting Engine 

The first problem many experience with their Stihl chainsaw is a hard-starting engine. Air bubbles usually cause this in the fuel system or a clogged carburetor jet.

To resolve this issue, you should check for air bubbles in the fuel line and clean any debris from the carburetor jets.

If these steps don’t solve your problem, you may need to correct the spark plug or perform other maintenance on your saw’s starting system. 

2. Poor Acceleration 

If your Stihl MS 391 isn’t accelerating while running, it could be due to a clogged muffler, worn spark plug wire, or damaged ignition coil

To diagnose the problem, you should check for any clogs in your muffler and replace any worn spark plug wires or ignition coils. 

If these steps don’t improve your saw’s acceleration, it could be due to a faulty air filter or an issue with the carburetor adjustment screws.

3. Low Power Output 

If your saw runs but doesn’t have enough power to cut through thick branches or logs effectively, it could be due to a few different factors. 

First, ensure that your chain bar and chain are properly lubricated—a dry chain will result in poor performance and increase wear on other components. 

Additionally, check for air leaks in the fuel system and worn-out gaskets in the engine housing, which can also reduce power output. 

Finally, if none of these solutions work, you may need to adjust the carburetor settings or replace certain parts, such as the piston rings or crankshaft bearings, if worn out.  

4. Overheating Engine 

Overheating engines are another common issue with Stihl MS 391 chainsaws.

 A build-up of dirt and debris around the engine housing or an inadequate cooling oil supply usually causes this.

To fix this problem, start by cleaning any dirt and debris around the engine housing using compressed air or a cloth dampened with water-based cleaner (NOT gasoline!).

Then check your saw’s oil levels and refill them if necessary—you should also change out any old oil for fresh oil at least once every season to keep your engine running smoothly and cool down better during use.

Finally, inspect all hoses leading away from the engine for cracks or holes, which could cause overheating due to reduced airflow over its surface area while running!  

5. Carburetor Problems

If your Stihl MS 391 isn’t running properly, the issue could lie within its carburetor

To diagnose this problem, check for any debris clogging up the jets or air filter and clean these out if found. 

You should also make sure that all the screws on the carburetor are tightened correctly and that the correct fuel/air mixture is used for your saw.

Finally, if all else fails, consider replacing your carburetor entirely to ensure it’s functioning correctly and not causing any issues with performance or power output.

6. Ignition Problems

If your Stihl MS 391 chain saw won’t start or is having difficulty with a spark plug, the ignition system may be to blame.

To diagnose this issue, check the spark plug wire for any signs of wear and tear and replace it if necessary. You should also examine the ignition coil and ensure no cracks or other damage.

Finally, if you find these components in good condition, the issue could be with the spark plug itself. In this case, consider replacing the spark plug to ensure it is up-to-date and operating correctly.

By following these steps, you’ll be able to solve any ignition problems your Stihl MS 391 chain saw may have.

7. Fuel and Oil Leaks

Leaking fuel and oil can cause several issues for your Stihl chains, such as poor performance or decreased power output.

Inspect all hoses leading from the engine to diagnose this problem for any signs of cracking or wear and tear. Additionally, check around the tank for any leaks and replace any gaskets that may be damaged.

Finally, make sure that your saw is using the correct fuel/oil mixture and change out any old oil for fresh oil at least once every season to keep your engine running smoothly.

8. Excessive vibration and noise

Loose or worn-out muffler screws, a damaged chain bar, or a bent crankshaft typically cause excessive vibration and noise.

Start by securely tightening all of the screws on your saw’s muffler to fix this problem.

Then check for any damage to the chain bar and replace it if necessary.

Finally, inspect the crankshaft and replace it if it is bent, as this often causes excessive noise and vibration.

9. Chain Problems

 A worn-out or damaged chain is one of the most common issues with Stihl MS 391 chainsaws. The first step to solving this problem is checking for any damage to the chain bar sprocket or the drive sprocket.

If those pieces look okay, ensure your chain is adequately tensioned and lubricated with bar and chain oil.

You should also check for dull spots on the chain teeth, indicating excessive wear and tear. 

If you find any of these issues, it’s time to replace the chain bar, drive sprocket, and the chain itself.

10. Starter Cord Problems

Any issues, such as an old or worn-out starter cord, a jammed recoil spring, or a faulty spark plug, can cause starter cord problems.

 To solve this problem, start replacing the starter cord if worn out.

 If the cord looks okay, check for any blockages in the recoil starter housing, and clean out any debris clogging up the works.

Finally, if all else fails, consider replacing the spark plug, as this is often the cause of many starting issues.

11. Poor Cutting Performance

Poor cutting performance can be caused by dull or blunt chain teeth, a loose chain baran incorrect fuel/oil mixture, or a dirty air filter.

To diagnose this issue, start by checking the sharpness of your saw’s chain and replacing it if necessary.

Then make sure that the chain bar is securely attached and that there are no loose pieces. 

After this, check the fuel/oil mixture to ensure that it is correct, and replace any old oil with fresh oil.

Finally, inspect the air filter for debris or dirt build-up and clean it off if necessary.

12. Air filter blockage

Among the most common problems with the Stihl chain is a blockage in the air filter. This can lead to engine performance issues, such as a loss of power or poor idling.

To diagnose this problem, check the air filter for any dirt or debris build-up and clean it off if necessary.

If the air filter looks okay, inspect other components, such as the spark plugfuel lines, and carburetor, to see if any of these are causing an issue.

Finally, ensure that your saw uses the correct fuel/oil mixture and replace any old oil with fresh oil at least once every season.

13. Spark plug faults

Another common issue with the Stihl MS 391 is a faulty spark plug. This can lead to starting issues, running problems, and poor engine performance.

To diagnose this problem start by inspecting the spark plug for any signs of damage or wear and tear and replacing it if necessary.

You should also check the spark plug gap to ensure it is set correctly, as an incorrect gap can lead to poor engine performance.

Finally, inspect the recoil starter housing for any blockages and clean out any debris clogging up the works.

Stihl MS 391 problems: Are they a deal breaker?

In conclusion, the Stihl MS 391 is a powerful and reliable chainsaw. That said, it does have its issues that can affect how well it works.

The most frequent Stihl MS 391 problems include engine difficulty starting, poor performance, and vibration issues. Furthermore, fuel tank caps can become loose or worn over time, causing leaks and other problems. 

In addition, spark plugs may need to be replaced due to misfiring or fouling. It is important to regularly inspect the saw for any signs of wear or damage to help prevent these issues.

When dealing with any problem related to your Stihl MS 391 chainsaw, it’s essential to remain safe while performing maintenance or repairs.

Make sure to wear protective gear such as gloves and goggles when inspecting the saw, and always follow instructions in your owner’s manual for any part replacements or adjustments.

By taking these steps, you can ensure that your Stihl MS 391 remains in good condition and ready to tackle any job you have. Inspecting the chainsaw regularly and ensuring that all parts are in working order is important.

We hope this article has inspired you to get back up and running quickly with as little stress as possible!

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( Farming Equipment Expert )

Marvin is an expert in farming equipment with a strong background in agricultural engineering. He graduated from Kansas State College of Agriculture, where he received a degree in Agricultural Engineering and specialized in farm equipment design and maintenance.