The Stihl MS 391 is a chainsaw suitable for professionals as well as homeowners or domestic users. The unique features of this chainsaw make them the best for all kinds of jobs. You can use them for your needs with no power sacrifice.
At some point in use, you may need to upgrade your Stihl MS 391 Chainsaw. Because, as they become old, their various parts may become less effective. By upgrading at this stage, you can get performances like a new one or even better.
In this article, I will discuss exactly which parts of the MS 391 chainsaw you need to upgrade or modify. I will also explain what additional benefits you will get because of this upgrade.
Before upgrading, it is necessary to know for what purpose you need to upgrade your chainsaw. Let’s get started.
Purpose Of Stihl MS 391 Upgrades
The main purpose of upgrading the Stihl MS 391 chainsaw is to increase its power and performance. You may know that the Stihl MS 391 chainsaw has a gas-powered 64.1cc two-cycle engine. This engine takes in air, which is mixed with fuel in the carburetor to power the chain drive.
So if you can ensure good airflow to the carburetor, the performance of the chainsaw will increase. Likewise, widening the inlets and outlets of the cylinders to allow the engine to breathe effectively increases the engine’s performance.
Also, modifications like air filter replacement, carburetor cleaning, and spark plug replacement ensure smooth operation of the chainsaw. In short, you will upgrade your Stihl MS 391 chainsaw to ensure more efficient and trouble-free smooth operation.
How Much Is Stihl MS 391?
Complete Guide Of Stihl MS 391 Upgrades
There are many who consider only a muffler modification to be a chainsaw upgrade. It is true, with muffler modification, you can increase the engine’s performance. But the upgrade requires more to ensure the smooth operation of your chainsaw.
I would like to describe here everything that you need to do to upgrade the Stihl MS 391. These are simple tasks and require the use of very few tools.
1. Prepare The Chainsaw
Leave it running for 5 to 10 minutes as part of preparing the chainsaw for upgrading. Then turn off the power of the chainsaw and remove the bar and chain. Now focus on cleaning your device.
Although after opening any part of the chainsaw you will need to clean the surrounding area, including those specific parts, clean the entire exterior first. You can use a blowgun to clean, if not use a clean cloth.
Open the fuel tank and drain the fuel. You can soak the cloth in this fuel to make the cleaning process more effective. Similarly, if you open any part, clean it well.
How Much Is Stihl MS 391?
2. Upgrade Carburetors
A good carburetor ensures proper engine efficiency. It controls the amount of gasoline entering the chainsaw engine. A faulty carburetor can make chainsaw difficult to operate. So upgrading the carburetor is quite important.
But you have to be careful while upgrading the carburetor. The wrong modification can even destroy your chainsaw.
To adjust the chainsaw carburetor you basically need to adjust the high-speed, low-speed , and idle-speed screws. Notice that the Stihl MS 391 chainsaw has a plastic limiter on top of these screws that prevents the screws from over-rotating. If you are not experienced enough, do not remove the limiters.
By adjusting the high-speed screw, you can determine how many rpm or speeds you want to operate while the chainsaw is at full throttle. Turning the screw clockwise will increase the rpm and counterclockwise will decrease the rpm.
The low-speed screw determines what RPM the chainsaw will be at idle. It is usually located away from the air filter and closer to the engine. Turning the screw clockwise decreases the rpm and counterclockwise increases the rpm. Properly adjusting the low-speed screw gives a better throttle response. That means the engine can go from low rpm to high rpm instantly.
The idle-speed screw adjustment allows the chainsaw to run more smoothly when idle. Also contributes to an easy engine start. This works like fine-tuning the low-speed screw. The video below can help you adjust the carburetor.
3. Upgrade Muffler
I have already said that modifying the muffler improves the breathing of the engine. As a result, the chainsaw’s torque and rpm increase. To upgrade or modify the muffler, first take it apart and clean it thoroughly.
All you need to do is enlarge the exhaust ports. Experts generally recommend a port diameter of about 40% to 80% of the muffler’s main exhaust outlet. Holes larger than this can affect the composition of the air-fuel mixture.
Use a 0.8-inch drill bit to do the job and a ruler for accurate measurements. Once the ports are enlarged, clean the spark arrestor screen as well. This will make the airflow much easier.
4. Adjust The Air Passage
The Stihl MS 391 chainsaw has a long plastic tab next to the carburetor screws. This prevents hot air from the engine from entering the air filter. The company recommends leaving it in place in the summer and removing it in the winter.
Air passage adjust refers to whether you keep this tab in place or not. If it is cold, remove it and clean it and store it. And if it’s summer, leave it in place.
How Much Is Stihl MS 391?
5. Replace Cylinder Fins
A chainsaw with damaged cylinder fins can cause the machine to leak fuel and air mixture into the crankcase. This type of problem can cause a chainsaw’s engine to lose power and have poor starting performance.
So check the cylinder fins well. If they are okay, then clean and reinstall. But if you find the fins are damaged, replace them.
6. Adjust Oiler
The oiler must function properly for the chainsaw to operate smoothly. Check if the oiler works well. I previously wrote a detailed article on how to adjust a chainsaw’s oiler. If you require an adjustment of the oiler, follow that article.
7. Replace the Air Filter & Spark Plug
Good quality spark plugs and air filters are essential to keep the chainsaw engine running smoothly. You can clean and reinstall the old air filter and spark plug if they are in good condition on your chainsaw. But I would suggest you replace them.
You can purchase a service kit of the Stihl MS 391 from hardware stores. These kits include an air filter, a spark plug, and a fuel filter. Remove the old air filter and spark plug, clean connection areas, and install new ones.
8. Replace The Fuel Filter
If you buy the service kit, you will get the fuel filter there. You can use a pair of long-headed pliers to replace the fuel filter. Before doing the work, drain the fuel tank completely.
Grasp the fuel line using pliers and pull it out. At the end of the fuel line, you will see the filter, pull it apart. Now attach the new filter and re-send the line back to the previous position.
The fuel filter does not allow contaminants into the engine. Because of this, the engine remains efficient for a long time.
9. Upgrade Bar And Chain
Bar and chain updates are very important topics for a chainsaw. The larger the chainsaw bar, the more power the engine must use to drive it. So don’t use too big bars unnecessarily.
Refer to the chart below to determine the best size bar for a gas chainsaw. This will help in sizing the bar based on the engine power.
| Engine type | CC limits | Compatible bars |
|---|---|---|
| Gas | 25 – 35 CC | 12 – 16 Inches |
| Gas | 35 – 45 CC | 12 – 18 Inches |
| Gas | 45 – 60 CC | 16 – 20 Inches |
Since the Stihl MS 391 chainsaw has a powerful 61 cc engine, you can use 16 to 20 eng bar and chain accordingly. But if you can get away with using a 16-inch bar, then it is better to avoid using a 20-inch bar.
Stihl MS 391 Manual
Detail Video About Stihl 391 Chainsaw with 25″ bar
Is a Stihl MS 391 a Pro Saw?
Yes, the Stihl MS 391 is a pro saw. It is easy to use and fuel efficient. That is why this chainsaw is equally recommended for professionals as well as casual users. You can use this chainsaw for any kind of cutting, big or small.
How Big of a Bar Can You Put on a Stihl MS 391?
I have already presented a chart above regarding bar sizes for Stihl MS 391. The powerful 64.1 cc engine allows you to use a 20-inch long bar on chainsaw with ease.
How Much Is Stihl MS 391?
Final Verdict Regarding Stihl MS 391 Upgrades
Here I have mentioned 9 points to upgrade Stihl MS 391 chainsaw. Apart from these, there are some other modifications or upgrades that can help improve the performance of your chainsaw, but they are not as important.
I strongly believe that by making these modifications, you can make your chainsaw stronger and more efficient. If you want to know more about this chainsaw upgrade, you can contact us in the comment section. I’ll get back to you as soon as possible.
