Stihl MS391 Upgrades

How can you proceed with your age-old Stihl MS391 upgrades? Undoubtedly, the muffler mod comes to mind at first. Right? Along with that, some other parts upgrading can be included in the list too.

However, this article will showcase all the important parts needed for upgrading and other essentials related to a step-by-step Stihl MS391 mod. Before starting, make sure you give your full attention to understanding each part.

Stihl MS391 Upgrades (Proper Steps)

Upgrading Stihl ms391 can convert it to a pro chainsaw. The best time to upgrade your chainsaw is in winter because we usually don’t use it in winter.

However, you can do it in your own free time. We will discuss the process below now on how to upgrade your Stihl ms391.

Essential Tools Needed For MS391 Upgrades

These six tools are essential for the modification of Stihl ms391. Such as:

  1. Rag
  2. Flathead Wrench
  3. Screwdriver
  4. Steel Bowl
  5. Torx Bits
  6. Steel service kit for ms391

Let’s start.

Preparing Machine

Before starting the modification process, make sure to warm up your machine. Set the brake on the chain by putting it on the ground. Squeeze the trigger and try to push all the way down to choke for warming up the saw.

You have to start it by priming for approximately 5 to 10 minutes. Buy a steel service kit from the hardware store. That service kit would contain a new air filter, spark plug, and fuel filter.

Open & Clean Up

 Firstly, wear thick gloves for your safety. Take out the chain and the bar carefully. Then open up the fuel tank and pour it out to a steel bowl. Soak a rag in fuel and clean up the machine.

 You can use any type of grease to clean, but I have found the best results with fuel. Especially, clean out the small areas where the chain was attached.

Change Fuel Tank, Air Filter & Spark Plug

Using a long needle nose plier, grab the fuel tank and pull it out. Carefully take out the old fuel filter and replace it with a new one. Afterward, seal the fuel tank with a new sealer.

Use the wrench to remove the old spark plug. Then rotate clockwise to take out the old air cleaner and replace it with a new air filter and new spark plug.

Change Carburetors

In the carburetor, there are limiter caps. We have to start with Stihl MS 391 carburetor removal. Use a screwdriver to remove the plastic screws above the carburetor.

Carburetors don’t need much modification like other parts. Replace the old carburetor only if you would modify the muffler for a speedy engine. However, carburetors need tuning to control the fuel and air for a better running engine.

Upgrade Muffler

Using a flat metal screwdriver, pull out the caps and Stihl ms391 muffler bolts from the bark box. Then use a T27 Torx to unscrew the muffler. Gently take out the muffler and gasket underneath it. After Stihl ms 391 muffler removal, clean up the muffler area and cut off the muffler steel using a Dremel tool. It will help it to exhaust better.

Make three slits and push it using a screwdriver to make the vent downwards. Put on the Stihl ms391 bark box and gasket. After that, gently put the muffler and screw it up. Instead of a single muffler, Stihl MS391 dual port muffler can be used for ventilation. It would give extra power to the chainsaw.

Modify Bar And Chain

 You have to search in the market for a big bar that would fit Stihl ms391 exactly without disturbing the whole balance ratio. A bigger bar would be able to cut wider trees in one go. After changing the bar, the next step is changing into a right fit chain.

Take off the big screw and put a new chain. Ensure the rakers like cutting teeth go on top of the bar. Then tighten the big screw. Put on the cover and small screws on. Pull up the hanging chain using a wrench in the small holes of the bar. Use a chain sharpener if the chain loses its sharpness. Lastly, place everything at its place and clean out the mess. Before using it on the tree, start it out on the ground to check the chainsaw.

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Frequently Asked Questions (FAQs)

How big of a bar can you put on a Stihl 391?

You can put a bar of 20 inches in length on a Stihl 391. By Stihl ms391 mod it’s possible to put a bar up to 20 inches. Above that, the machine would not be able to balance the weight. But a 20-inch bar is good enough to cut large trees.

Is the ms391 a pro saw?

No, the ms391 is not a pro saw. However, it is known as a semi-pro saw. It is easy to manage and contains high torque for better usage. Also, it consumes 20% less fuel. So, undoubtedly ms391 is a good semi-pro chainsaw.


Last but not least we want to suggest you is modify it according to your use of the chainsaw. If you think your old Stihl ms391 muffler isn’t good enough for your use, undoubtedly Stihl ms391 muffler mod is the best option among all Stihl MS391 upgrades.

Besides, for better performance, it’s not necessary to upgrade the bar and chain for cutting small trees. So, you can skip modification parts according to your need.

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