Why Is My Lawnmower Shooting Flames? Expert’s Interview


Lawnmowers are sensitive machines, and every part plays an important role in running the engine smoothly. If anything happens to any of the components, it may prevent you run the machine smoothly.

Why is my lawnmower shooting flames?

One of the main reasons could be that the exhaust system is filled with unburnt fuel, ultimately causing firing issues. Since it is a serious issue, you want to address it soonest to prevent damaging the exhaust manifold and other components.

Why Is My Lawnmower Shooting Flames?

Lawnmower Backfiring

There could be several reasons your lawnmower is shooting flames. Since it could lead to dangerous accidents, you want to address it soonest. Here are all possible reasons when you want to know about “Why is my lawnmower shooting flames?”

1. Giving More Pressure

Are you giving more pressure to the lawnmower? When you mow grass for several hours without any single break, the engine becomes excessively hot.

As a result, the piston moves slowly, and it fails to comply with the firing cycle of the spark plug. Some portion of fuel fails to burn and moves to the exhaust system without burning.

Finally, when the ignition system starts, your lawnmower is likely to shoot flames. The earlier you stop the machine, the better it is.

2. Cutting Tall And Thick Grasses

Cutting Tall And Thick Grasses

Do you cut tall and thick grasses often? Have you checked whether the mower deck doesn’t stick anything?

If the blazing hot muffler is completely filled with grasses, your lawnmower has a probability of shooting flames. At worst, this may burn out the lawn too.

3. Fuel Hazards

The normal stability of a lawnmower motor is compromised if fuel leaks in the engine. This can lead to flame. In addition, if a hot muffler is surrounded by fuel vapors, it can also cause a flame.

4. Excessive Fuel

Initially, if excessive fuel exits inside the combustion chamber, your mower may shoot flames. So, why it occurs? It occurs when the air-fuel mixture becomes excessively rich from the adjustability of the carburetor.

5. Poor Performance Of Spark Plugs

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Are the spark plugs performing the way they should be? If there is a lack of oxygen, incomplete combustion occurs, making the spark plug weak or misfiring.

At first, this will lead to smoking. Then extra heat is generated, making the exhaust hotter. At last, flames will come out from the exhaust pipe.

6. Using Old Fuel

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Are you using too old fuel for your mower? Changing fuel is necessary once a month. Old fuel may lose its quality when it sits idle for a long time. Using this old fuel can cause smoking issues and ultimately shoot flames.

So, these are the possible causes you want to check out if you wonder, “Why is my lawnmower shooting flames?”

What Does It Mean When Your Lawnmower Backfires?

Is your lawnmower backfiring? Not taking immediate action will lead to heavy damage to your mower.

What does it mean when your lawnmower backfires?

When your lawnmower engine backfires, it is failing to generate the same amount of power it used to do. As a result, fuel inefficiency occurs, and the machine uses more fuel to produce energy. You may also hear loud popping noise coming out from the mower.

So, what are the signs of misfiring a lawnmower? You can understand whether your lawnmower is misfiring or not by checking out these symptoms:

  • The unpleasing smell coming from the mower
  • The mower makes unusual sounds when it runs on
  • The engine is losing its power
  • You may struggle to start it
  • the exhaust pipe is releasing an excessive amount of smoke

You have already learned about “What does it mean when your lawnmower backfires?” and “What are the symptoms of misfiring lawnmower?”

Here are the possible reasons you should check to learn to find the reason behind misfiring issues in your lawnmower.

1. Imperfect Air/Fuel Mixture

You should neither have a high or low air/fuel mixture. The ratio should be stable — not too low or too rich.

If there is a low air/fuel mixture, the engine has less fuel but high air. Imbalanced ratio. This may happen due to low fuel pressure. It is also known as “lean mixture.”

When it happens, some fuel and air fail to reach inside the exhaust valves at the right time as they burn slowly. As a result, backfiring occurs.

2. Bent Valve Or Valves

Bent Valve Or Valves

A lawnmower has several cylinders, and each cylinder includes one exhaust valve and one intake valve.  The job of an exhaust valve is to pass burned gases from the cylinder.

On the contrary, the intake valve enables an ideal air-fuel combination to enter the cylinder.

However, when a valve vent, it doesn’t have a perfect close or opening. As a result, the fuel fails to pass through the exhaust or intake valve to combust. This leads to backfiring issues.

3. Wrong Ignition Timing

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When wrong ignition timing occurs, the spark will fire either too late or too late. In both cases, the intake or exhaust valve may combust, causing backfiring. You can’t diagnose this problem unless you are a professional mechanic.

4. Older Lawnmower

Are you using an older lawnmower? Latest lawnmowers are tuned up finely through computer systems. That’s why they can constantly adjust their internal system to make the mower run smoothly.

However, the older lawnmower may not do this like the latest models. They often fail to control the sparks when it is fired and the perfect air-fuel ratio.

Read More – What Are The Best Lawn Mowers For Small Yards?

5. High Engine Temperature

High Engine Temperature

Commonly, your lawnmower temperature will rise when you use it. But if the temperature increases unusually, there is something concerned.

When this happens, you may notice the engine is backfiring and automatically shut down after running for several minutes.

Can A Backfire Damage An Engine?

The backfiring issue occurs for several reasons, which we have already discussed above. It will prevent you from running the machine normally.

Can a backfire damage an engine?

A backfire can damage the engine heavily if neglecting the issue for a prolonged time. You want to address the problem as early as possible to prevent damaging it completely.

How to stop backfiring issues for your lawnmower? Here are a few points you want to apply if your lawnmower is backfiring and save from extra damage.

1. Adequate Oxygen

Does your lawnmower have the perfect amount of oxygen? An ideal amount of air fuel is required to run the mower smoothly. It should be neither too rich nor too low.

When the oxygen level drops, excessive fuel will enter the system. Also, a high level of oxygen (air) will prevent entering an adequate amount of fuel.

2. Air leakage

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Is Your Mower Has Air Leakage? If there is any leakage issue, you want to solve it soonest.

3. Replace Spark Plugs

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Replacing spark plugs after a certain time is necessary. Over time, its construction weakens due to long-time use.

Using new spark plugs ensure perfect spark firing at the right time, also preventing backfiring issues.

4. Maintaining A Healthy Exhaust

Maintaining A Healthy Exhaust

The exhaust system is one of the most common parts where backfire occurs. This mainly happens when the exhaust system is unhealthy.

Proper functioning will be carried out because of this. That’s why maintaining a healthy exhaust system for your lawnmower is necessary.

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Hopefully, you have learned about “Can a backfire damage an engine?” and how to stop this issue.

Can A Lawn Mower Explode?

Can A Lawn Mower Explode?

Explosion for any engine can damage it and even make the owner heavily injured.

Can a lawnmower explode?

Yes! A Lawnmower can explode if it is a gas-powered rotary mower. If a leakage issue is seen in the gas tank, it may fire and create a small explosion.

While filling the gas tank, you want to make sure no spelling issues. Being uncareful, you may splash it on the hot muffler, causing firing issues and explosion.

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The tall grass is one of the primary reasons that could lead to a fire in the lawnmower. That’s why it is better to mow your lawn regularly, ensuring good conditions for your lawn and mower.

So, why do tall grasses cause firing and explosion issues?

The taller the grasses, the bigger the grass clippings. As a result, bigger grass clippings will stick inside the deck and enter the hot motor, muffler, or exposed parts.

When the clippings contact with the hot parts, they start to burn. After a certain time, they will catch fire and may result in an explosion.

Weather condition is another important thing you should note down. You need to choose a perfect time to mow your lawn, especially in the summer season.

During the season, the temperature becomes excessively hot, especially in the afternoon hours. That’s why you want to either mow the lawn in the early morning or evening hours to prevent excessive heat.


Everyone wants to run their machine without any issues. Sometimes unwanted problems pop up from the engine. Resolving it soonest is what we are supposed to do. Hopefully, you have learned everything about “Why is my lawnmower shooting flames?” and how to deal with the problem.

Last update on 2021-09-30 / Affiliate links / Images from Amazon Product Advertising API