Why Would a Chainsaw Backfire? (Discover the Main Reasons)

If your chainsaw just backfired and went off, you might be probably wondering why would a chainsaw backfire?

Backfire on a chainsaw occurs due to two main reasons. First, the flywheel key shears and stop the engine’s rotation. Second, a faulty carburetor with messed-up timing also causes a backfire.

Both of these reasons can be quite problematic and will require some repair in order to get your chainsaw back up and running again. In the meantime, here are a couple of things you need to know about a chainsaw that backfires.

I highly recommend you keep reading as it will help you understand the issue from different angles.

Why Would a Chainsaw Backfire

Why Would a Chainsaw Backfire?

When the flywheel key shears, it’ll cause the engine to stop rotating. This can be a result of several things, but usually, it’s because the chainsaw was jammed and you were trying to force it through the material.

Sheared flywheel key is a common issue and it’s usually not too difficult to replace. However, if the key shears, it can damage the crankshaft and cause other problems.

Another reason why your chainsaw might backfire is a faulty carburetor. This is usually because the carburetor isn’t adjusted properly and the timing is off.

A carburetor that’s not working correctly can cause all sorts of problems, including backfire. This is a serious issue and it needs to be fixed as soon as possible.

In most cases, a backfire on a chainsaw is caused by one of these two reasons. However, there are other potential causes as well.

  • For example, a damaged muffler or ignition system also causes a backfire.
  • The same goes for a weak or damaged spark plug.

If you’re not sure what’s causing the backfire, it’s best to take the chainsaw to a qualified technician and have them take a look at it.

What Does It Mean When A Chainsaw Backfires?

Generally, the backfire of the saw is confused with after fire which is caused by the unburnt fuel that reaches the hot muffler. But the question is that what is the backfire in a chainsaw.

When a chainsaw backfires it usually means that the carburetor has timing issue which is not allowing the fuel and air mixture to enter the cylinder at the right time.

It is simple when the piston of your chainsaw reaches the top of its stroke and starts moving back down, the intake valve opens to allow fresh air-fuel mixture into the cylinder.

As the piston moves downward, it compresses this mixture until it reaches a point where it’s volatile enough to ignite. At this point, the spark plug ignites the mixture and forces the piston back up on its compression stroke.

If for some reason the mixture is not ignited by the spark plug, it will simply continue to compress until the piston reaches the top of its stroke again. When this happens, the intake valve will open and allow fresh mixture into the cylinder, starting the cycle all over again.

a might stihl chainsaw

Let’s Understand the Backfire

Now, if the carburetor is not timed correctly, the mixture will enter the cylinder too early or too late. If it’s too early, the mixture will simply be forced back out through the intake valve when the piston starts its compression stroke.

This is known as “pre-ignition” and it can cause all sorts of problems, including backfire. If the mixture enters the cylinder too late, it will compress until the piston reaches the top of its stroke and then ignite.

This is known as “after-fire” and it can also cause backfire. In most cases, after-fire is caused by unburnt fuel reaching the hot muffler. Either way, backfire is a serious problem and it needs to be fixed as soon as possible.

How To Fix Backfire In Chainsaw?

The first thing you need to do is identify the cause of the backfire. As we mentioned earlier, most backfires are caused by either a sheared flywheel key or a faulty carburetor.

If you’re not sure what’s causing the backfire, it’s best to take the chainsaw to a qualified technician and have them take a look at it. Once you know the cause of the backfire, you can take the necessary steps to fix it.

For example, if the backfire is caused by a sheared flywheel key, you’ll need to replace the key. If the backfire is caused by a faulty carburetor, you’ll need to adjust the carburetor or replace it entirely.

Why Does My Chainsaw Stop Running After A Few Minutes?

Sometimes you may encounter a strange problem when using your chainsaw. It may stop running after a few minutes and you might be worried about it.

There could be a couple of reasons that cause the chainsaw to stop running after a few minutes. Some of them are mentioned below:

  1. The air filter of the chainsaw might be dirty and it needs to be replaced.
  2. The spark plug might be damaged or fouled and it needs to be replaced.
  3. The fuel mixture might be incorrect and it needs to be adjusted.
  4. The carburetor might need to be cleaned or rebuilt.
  5. The ignition system might be faulty and it needs to be repaired.

How Do I Know If My Chainsaw Carburetor Timing Is Incorrect?

Another common problem that most beginners may face while operating a chainsaw is the misalignment of the chainsaw carburetor timing. It can be the root cause of various issues therefore, you need to ensure that your carburetor is timed correctly.

But the problem is you don’t know how to check if the carburetor of your chainsaw is timed correctly or not. Well, here are a few things that you can do in order to check the timing of your chainsaw carburetor:

First of all, you need to find the TDC mark on the flywheel of your chainsaw. Once you have found it, you need to align it with the mark on the chainsaw’s body.

investigating a chainsaw backfire

Now, you need to remove the spark plug of your chainsaw in order to check the position of the piston. Once you have removed the spark plug, you need to insert a small rod into the cylinder through the spark plug hole.

You need to rotate the flywheel until you feel the piston hit the rod. Once you have found the TDC, you need to mark it with a pencil or anything else.

Now, you need to remove the rod and put the spark plug back in its place. After that, you need to rotate the flywheel until the TDC mark on the flywheel aligns with the mark on the chainsaw’s body.

Now, you need to look at the carburetor and see if the piston is in the correct position. If it’s not, you need to adjust the carburetor until it’s in the right position.

How Do You Adjust The Air Fuel Mixture In A Carb?

The carburetor is responsible for mixing the air and fuel in the right ratio. If the mixture is too rich or too lean, it can cause all sorts of problems.

Therefore, it’s important to adjust the air-fuel mixture in your carburetor from time to time. Here’s how you can do it:

First of all, you need to find the idle mixture screw on the carburetor. Once you have found it, you need to turn it clockwise or counterclockwise until you find the sweet spot.

The sweet spot is the point where the engine runs smoothly. You need to be careful while adjusting the mixture screw because if you go too far, you might end up making the mixture too rich or too lean.

If the mixture is too rich, it can cause the engine to bog down and if it’s too lean, it can cause the engine to overheat. Therefore, you need to be careful and adjust the mixture screw until you find the sweet spot.

Conclusion

So why would a chainsaw backfire? A chainsaw backfires due to a faulty carburetor, incorrect fuel mixture, or damaged spark plug. You’ll need to adjust the carburetor or replace it entirely.

In this article, we have discussed some of the common reasons that can cause a chainsaw to backfire. We have also discussed how you can fix some of the common problems that can cause a chainsaw to backfire.

I hope this article was helpful and you were able to find the answer to your question. If you have any further questions, feel free to ask in the comments section below.

Thanks for reading!

References

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Jack Logan is a student of MS Global Navigation Satellite System who spends his free time researching and writing articles, many of which are geared towards helping people. His favorite power tools are miter saws and impact wrenches Read More About Jack