You’re in the middle of a project, only to have your chainsaw die on you because the plug keeps fouling. It’s a frustrating experience. So, what can you do to prevent this issue?
You can fix fouling plugs by cleaning the air filter, replacing the pistol ring, or unflooding the oil chamber. You can also resolve issues with the fuel mixture or tune your chainsaw. Of course, the solution depends on the problem causing the fouling plugs.
In this article, I’ll discuss what causes a Stihl chainsaw to keep fouling plugs. I’ll also explore ways you can fix this when it happens. Read on to learn more!
What Causes a Stihl Chainsaw To Keep Fouling Plugs?
There are different reasons your Stihl chainsaw may be fouling plugs. Let’s take a closer look at each of them.
There Are Fuel Mixture Errors
One reason for the fouling plug is that a rich mixture can deposit oil on the spark plug. Another reason is that the fuel mixture can lead to a build-up of carbon on the spark plug. Both of these can cause the plug to misfire and your Stihl chainsaw to not work as well as it should.
The Air Filter Is Dirty
You’ll know your chainsaw’s air filter is dirty if the engine runs lean and produces too much carbon.
If your air filter is dirty and clogged, it’ll hinder the supply of air to the engine. As a result, unburned fuel forms soot build-up on the spark plug. This causes the plug to foul, interfering with the process of engine combustion.
The Engine Oil Is Leaking
If your Stihl chainsaw leaks oil, it’s likely causing the spark plug to foul as well.
An engine oil leak can happen if the oil level is too high or the oil seal is damaged. Too much oil can cause the engine to run hotter or misfire, eventually leading to engine damage.
A Worn-Out Piston Ring Might Be the Problem
If your Stihl chainsaw is continually fouling plugs, it’s likely due to a worn-out piston ring.
The piston ring seals the combustion chamber and keeps the fuel and air mixture from leaking. When the piston ring is worn out, it can no longer seal the chamber.
A worn-out piston ring can cause the piston to lose compression, allowing the fuel and air mixture to escape. This can cause the mixture to become too rich, causing the spark plug to foul.
The Spark Plug Has Deteriorated
When a spark plug is overused, the metal tip can erode, and the electrode becomes worn. This can cause the spark plug to produce a weaker spark and foul more easily.
As a result, the spark plug cannot ignite the fuel properly, resulting in a build-up of unburned fuel on the plug.
Over time, the spark plug can become covered in carbon deposits. Carbon build-up on the plug reduces its efficiency and causes issues like hard starts, misfires in the engine, and poor acceleration.
6 Ways to Fix a Stihl Chainsaw that Keeps Fouling Plugs
1. Resolve the Fuel Mixture Problem
If the fuel mixture is too lean, it can cause the engine to run lean and foul the spark plugs. You can correct the problem by mixing the fuel at the correct ratio.
According to the Stihl shop, the correct ratio for a fuel mixture is 1:50 (source). In other words, you need to mix 50 parts gas with 1 part oil.
Alternatively, if your chainsaw is running on a lower-octane fuel, mix the fuel at the correct ratio and use fresh, high-octane gas. Stihl recommends using no less than 89 octane fuel (source).
2. Check the Oil Level
If the plug fouling is due to a flooded combustion chamber, you’ll want to unflood it.
To do so:
- Take off the cover.
- Set the machine idle.
- Remove the spark plug. Your machine is flooded if you see the gas on the plug.
- Pull the cord a few times. You can do these 10 to 15 times in a row.
- Let your machine rest for a few seconds, and then pull the cord again. The excess oil should come off at this point.
- Finally, re-install the spark plug and start the chainsaw.
Alternatively, you can check out this YouTube video on how to fix a flooded Stihl chainsaw engine:
3. Clean the Air Filter
A clean-up of the air filter can save you not only from a fouling plug but also a lot of frustration.
Here are a few ways to clean the air filter on your Stihl chainsaw:
- Remove the filter and soak it in a mixture of soap and warm water.
- Use a brush to remove debris from the filter.
- You can also use a compressed air canister. I recommend the Gumout Carb and Choke Cleaner (link to Amazon). I like that it dries pretty quickly, so you’re not left with too much of a mess to clean up afterward.
4. Replace the Piston Ring
If your piston ring is worn-out, it may be time to replace it. This is a relatively easy repair you can do at home with a few tools.
To replace the piston ring:
- Remove the spark plug and unscrew the flywheel’s two nuts.
- Remove the cylinder cover and the piston. The piston ring is located on the piston. You can pry it off with a flat-head screwdriver.
- Once the old ring is off, clean the piston and the cylinder.
- Install the new piston ring by gently tapping it into place. Be careful not to damage the ring.
- Reassemble the chainsaw and test it out.
5. Replace the Plug
Stihl recommends changing the spark plug after every 100 hours of use or annually, whichever comes first. You will have to find specific guides for this based on your model of chainsaw.
6. A Tune-up Can Help Resolve the Problem
It may be time to tune up your Stihl chainsaw.
A typical tune-up includes:
- Cleaning or replacing the air/fuel filters
- Troubleshooting the carburetor
- Assessing the spark plug
- Sharpening and lubricating the chain
This preventative measure can help keep your saw running smoothly.
However, if you’re uncomfortable performing a tune-up yourself, you can take your chainsaw to a certified Stihl dealer for service.
Conclusion
If your Stihl chainsaw keeps fouling plugs, replacing the plug may be a good idea. You can also check the fuel mixture and ensure it has the correct gas-to-oil ratio. It would also help if you clean or replace the air filter if that’s the source of the problem.
Of course, whichever approach you take will depend on the root of the issue. So, take your time to assess what could be wrong before fixing the foul plug. That way, you can fix the problem accordingly and get your chainsaw running smoothly again.
Chainsaw cords breaking is another common problem many users experience. Read my guide to learn more about the reasons and solutions to fix it.
