5 Common Stihl MS 661 Problems and Solutions to Fix Them

You’ve just received your new MS 661 and are eager to produce mulch from the overgrown juniper in your front yard. You get to work, rev the engine, and begin clearing the heavy undergrowth. After a few minutes, you realize that the chain isn’t spinning, and the speed isn’t as fast.

“Why is this happening?” you wonder.

Well, most chainsaw owners are aware of the Stihl MS 661 issues. Some of them are as follows:

One of the most prevalent issues with your Stihl MS 661 is a failure to start, as well as sluggish acceleration. Furthermore, there is no chain rotation, the engine does not achieve maximum rpm, and so on.

I’ll examine some of those problems and discuss ways to completely resolve them, in the remaining sections of this post.

stihl ms 661 oroblems

Quick Table of Stihl MS 661 Problems and Possible Reasons

The Stihl MS 661 is a high-quality, versatile, and reliable chainsaw. As with all other tools, proper maintenance is required to prevent problems from occurring. Here are some of the most common Stihl MS 661 problems:

Stihl MS 661 Problems Possible Reasons
Failure to start Reasons may include spark plug problems, insufficient fuel, or a flooded combustion chamber
Poor acceleration Reasons may include poor chain tension or low oil feed
Chain not rotating Reasons may include poor chain tension, blocked bar nose sprocket, or engaged chain brake
A burning smell is released when cutting Reasons may include dull chain blades, insufficient chain lubrication, or an over-tensioned chain
Engine struggling to reach Max RPM Reasons include an improperly calibrated chainsaw or a dirty air filter.

Step-By-Step Guides and Solutions to Stihl MS 661 Issues

Before attempting to make any repairs to your Stihl MS 661 chainsaw, make sure you have the following tools at your disposal:

Tools for Fix Stihl MS 661 Issues
  • Flat and Phillips head screwdrivers;
  • A pair of pliers;
  • An appropriate size wrench to screw and unscrew the spark plug if needed;
  • A clean microfiber towel and warm water for cleaning the parts;
  • Safety gloves and eye protection.

Now, let’s discuss each issue in further depth, along with potential solutions.

  1. Failure To Start

One of the most frequent problems that chainsaws face is having a hard time starting up. Many users have this problem, and the most common reasons are the spark plug, the combustion chamber, or the lack of fuel.

How to fix the starting problem

How to fix the starting problem

There are several things you can do in case your chainsaw has starting problems (even though it has enough fuel):

  1. Engage the chain brake.
  2. Remove the cover for the spark plug and the filter.
  3. Pull and remove the spark plug boot and unscrew the spark plug.
  4. Check the spark plug, let it dry (if wet from gasoline), or replace it if needed.
  5. Move the master control lever to position and pull the starter grip.
  6. Pull the starter grip several times while holding the master control lever in position. This will clear the combustion chamber.
  7. Insert the spark plug back into the hole, tighten it, and put the boot on firmly.
  8. Return the cover to its original position, and check how the chainsaw starts.

Read Also: Stihl MS 391 Problems, Troubleshooting With Solutions

  1. Poor Acceleration

If you notice that the chain on the chainsaw has poor acceleration, then the reason for that might be an over-tightened chain. The chain also may not get sufficient oil to run smoothly and accelerate quickly on the blade.

Poor Acceleration

How to fix poor chain acceleration

Here’s how to properly tension the chain and fix poor acceleration:

  1. Locate the tensioning screw on the side of your chainsaw. It should be the one in between the two blade-tightening bolts.
  2. Turn the tensioning screw counterclockwise, and loosen it until the chain on the underside of the blade starts to hang freely.
  3. Now start tightening the screw in a clockwise direction until there is very little chain sag left on the underside of the blade.
  4. Using a pair of gloves, feel how loose or tight the chain is and adjust as needed.
  5. Try and see if this solves the chain acceleration problem.

Read Also: Stihl Chainsaw Oiler Adjustment

  1. Chain Not Rotating

One of the Stihl MS 661 problems that might be closely related to the previous one is that the chain may not rotate when you engage the throttle.

In this case, you may first want to check the chain’s tension, which we’ve explained in the previous section.

However, other reasons may cause this problem, like a buildup of debris in the bar nose sprocket, or maybe the chainsaw brake is engaged.

Chain Not Rotating

How to fix the lack of chain rotation when the throttle is engaged

  1. The first thing to do is check and ensure that the chain brake is not engaged.
  2. If the problem persists, proceed to disassemble and remove the chain.
  3. Start loosening the chain tension by turning the tensioner screw in a counterclockwise position.
  4. Unscrew and remove the blade-tightening screws and the sprocket cover.
  5. Remove the chain and the blade together using a pair of gloves.
  6. Clean the bar nose sprocket with an alcohol-based solvent.
  7. Reassemble everything in reverse order and try how the chainsaw operates.

Read Also: Best Chainsaw for Cutting Firewood – Top Choice in 2022

  1. A Burning Smell Is Released While Cutting

If you start noticing a smell of burnt wood when you cut with the chainsaw, then dull blades are the most common reason for this problem.

Insufficient lubrication can also be the reason for burning the wood, as the blades get hot and dull much more quickly.

A Burning Smell Is Released While Cutting

How to fix the burning smell when cutting

  • The first thing to do is try to sharpen the chain blades using the right technique. Make sure to wear gloves at all times.
  • After you’ve sharpened the blades, check to ensure enough oil is in the lubricating tank.
  • Ensure the oil feeding rate is properly calibrated so that enough oil is sent to lubricate the chain.
  • Check the chain’s tension and tension it properly if needed, following the steps in the previous section.

  1. The Engine Is Struggling To Reach The Maximum Rpm

If the Stihl MS 661 engine is having power issues and trouble reaching maximum RPM, then the reasons behind it may be improper carburetor calibration or a dirty air filter. So, this is one of the several possible Stihl MS 661 problems; thus, here’s how to fix it.

The Engine Is Struggling To Reach The Maximum Rpm

How to fix maximum engine RPM issues

  1. The first thing to do is to clean the air filter.
  2. Remove the plastic cover at the back of the chainsaw, and you will gain access to the filter.
  3. Clean the air filter with a soft brush; if it’s too dirty, you can also soak it in warm water and clean it thoroughly.
  4. Let the filter dry completely before installing it back in the chainsaw.
  5. If the problem persists, you can proceed to calibrate the carburetor (optional).
  6. Note that carburetor calibration is not a simple process. We will not go into much detail about it, but if you wish to try it, then the link we provided has all the instructions you need.


How to calibrate a Stihl 661?

Calibrating your Stihl 661 is a simple and straightforward process that will help you get the most out of your saw. The initial step is to turn on the machine. Keep it running for at least 90 seconds in the cold start position, without pressing the throttle or speeding the saw. That’s it!

How much of a bar can I set on a Stihl 661?

The 661’s max length is 36 inches, and it has a 20-inch arbor meaning you can put on anything from 20-inch bars up to 36-inch bars. Therefore, you can fit a whole lot of bars on this saw.

Is Stihl MS 661 fuel efficient?

The M-TronicTM technology of Stihl MS 661 provides 20% fuel economy with reduced vibration, which is a strong benefit. Additionally, with a 28.7-ounce fuel capacity, you can chop down trees all day long without having to worry about running out of fuel.


Stihl MS661 is a handy device that can be used for completing different cultivating and auxiliary works around the house and in the garden.

However, there are some troubles with this device arising from which you have to know the way out of these troubles.

Now, after this little instruction, I hope you’ll have a chance to learn all the Stihl MS661 problems and their solutions so that the cuttings made by your chainsaw always turn out as they are supposed to.

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