If your lawn mower’s exhaust pipe releases gas, you may be exposing yourself and your family to harmful air pollutants. These pollutants can cause a variety of health problems, including respiratory irritation, headaches, and fatigue. In some cases, they can also aggravate chronic conditions like asthma and heart disease.

Gas emissions from lawn mowers can contribute to smog formation, which can worsen air quality and lead to even more health problems. Like many other people, you are probably also wondering, “why is gas coming out of my lawn mower exhaust.”

It is important to make sure that your lawn mower is in good working condition and that the exhaust is properly vented. There are several reasons why this could be happening, and we will explore them below.

Why is Gas Coming Out of My Lawn Mower Exhaust : Some Reasons

Why Is Gas Coming Out Of My Lawn Mower Exhaust Some Reasons

Dirty Air Filter Passage:

The air filter helps to prevent getting dirty from entering the engine. It can re-ignite and release gas from the exhaust if not replaced or cleaned regularly. This gas can be harmful to humans and pets. Otherwise, you may end up with a lawn mower that releases unsafe gas into the air.

Damaged or Weak Spark Plug:

If the spark plug is damaged or weak, it can’t create a strong enough spark to ignite the fuel properly as spark plugs ignite the fuel mixture in the cylinder, which powers the engine. The engine may also be forced to escape gas from the cylinder and into the exhaust.

Faulty Needle Valve: 

If the fuel shut-off valve is damaged or not working properly, gas can leak from the exhaust, stopping the fuel flow when the engine is not running. If the valve may become clogged with dust and particles, gas can enter the engine and be forced out through the exhaust.

Carburetor Flooding: 

Due to carburetor flooding, gas comes out of your lawn mower’s exhaust. This typically happens when the engine is turned off while fuel is still present in the carburetor. Carburetor flooding can also be caused by a damaged gasket or a loose connection in the fuel line.

Dirty or Damaged Fuel Filter:

Dirty or Damaged Fuel Filter

The fuel filter is responsible for keeping impurities out of the fuel system; over time, it can become clogged with dirt and debris. If this happens, it can restrict fuel flow through the engine, causing the engine to run lean. When an engine runs lean, it doesn’t have enough fuel to combine with the air, resulting in unburned fuel as gas is expelled through the exhaust.

Warped or Damaged Cylinder Head:

When you see a gas leak from your lawn mower exhaust, it’s usually an indication that the cylinder head is warped or damaged. The cylinder head is what houses the spark plugs and valves, and it’s also where the air and fuel mixture is compressed. 

If the cylinder head isn’t sealing properly, it can cause the engine to run lean, which means there’s more air than fuel in the mixture. This can lead to a number of problems, including pre-ignition, piston damage, and excessive wear on the valves and cylinder walls. In some cases, a warped or damaged cylinder head can also cause the engine to backfire.

Fast Running Engine:

If too much gas is released, the engine is running too fast and not burning the fuel efficiently. As a result, not only will your lawn mower consume more gasoline, but it will also produce more harmful emissions.

Oversized Piston:

If gas comes out of your lawn mower’s exhaust, it is likely due to an oversized piston. This can happen if the wrong size piston is installed or the piston becomes damaged and enlarged. When the piston is too big, it results in too much mixture being pumped into the cylinder.

The engine can run too rich, resulting in the exhaust gas. The piston will no longer fit snugly in the engine cylinder, allowing gas to escape through the exhaust. In some cases, an oversized piston can also cause engine damage.

Leaking Head Gasket:

Leaking Head Gasket

The head gasket seals the combustion chamber and prevents engine gasses from escaping. If the head gasket is damaged, engine gasses can leak into the cooling system and out through the exhaust. A leaking head gasket can also cause your engine to overheat.

Dirty Oxygen Air Flow Sensor:

The oxygen air flow sensor measures the amount of oxygen in the engine’s exhaust. If the sensor is dirty, it may not be able to accurately measure the oxygen levels, which can lead to an overly rich fuel mixture. This can cause gas to leak from the exhaust.

Failing Catalytic Converter:

The catalytic converter is responsible for converting harmful gasses into less harmful gasses before they are released into the atmosphere. When the converter begins to fail, it can cause a build-up of pressure in the engine, which can cause gas to be expelled from the exhaust. It is also possible for a failing converter to cause excessive engine heat, which can damage other components.

Faulty Fuel Injector:

The fuel injector is responsible for delivering fuel to the engine. If it is not working properly, gas will leak into the exhaust system and be expelled through the muffler. In some cases, this can also lead to engine damage.

Fuel Pressure Sensor:

The fuel pressure sensor is responsible for regulating the flow of fuel within the engine. Fuel can leak into the exhaust. While this may seem like a minor problem, it can actually cause serious damage to your engine, letting gas come out of the lawn mower exhaust.

Throttle Position Sensor:

Throttle Position Sensor

The engine has a throttle position sensor (TPS) that tells the engine how much fuel to inject into the cylinder. If the TPS is faulty, it can cause too much fuel to be injected, leading to gas leaking out of exhaust pipes. 

Damaged Throttle Pump:

If gas is coming out of your lawn mower, it’s likely due to a damaged throttle pump. This pump is responsible for delivering the correct amount of gas to the engine. If it’s not working properly, the engine may also run erratically or stall.

Failing Fuel Pump:

If the fuel pump is not functioning correctly, gas can leak into the engine and come out from the exhaust. As the fuel pump is responsible for delivering gasoline to the engine, and if it isn’t working properly, the engine may not get the fuel it needs. This can cause the engine to run lean, leading to increased exhaust emissions.

Clogged Fuel Line:

A clogged fuel line is the most likely cause of fumes coming out by exhaust. Over time, dirt and debris can build up in the fuel line, restricting the flow of gas to the engine. As a result, the engine will run hotter than normal, causing the gas to vaporize and exit through the exhaust.

Failing Ignition Coil:

If it’s malfunctioning, gas may leak into the exhaust system. The ignition coil is responsible for providing a spark that ignites the fuel in the engine. If you notice gas coming out of your lawn mower’s exhaust, it could be a sign that the ignition coil is failing.

Spark Plug Gap:

Due to a spark plug gap, gas is coming out of your lawn mower’s exhaust. When the gap is too wide, it allows gas to escape from the engine, resulting in an increased risk of fire.

Air Intake Leak:

Due to an air intake leak, the carburetor does not get enough air, so it starts pulling gas from the fuel tank. The gas then gets mixed with the oil in the engine and ends up in the exhaust.

Worn Out Timing Belt:

The timing belt is a small but important part of the engine that controls the timing of the spark plugs. Over time, the belt will stretch and eventually break. When this happens, the engine will backfire, and gas will come out of the exhaust.

Overfilling the Gas Tank:

Overfilling the gas tank is a common mistake, raising issues such as gas leaking from the exhaust. This is because the extra gas has nowhere to go and is forced out of the engine through the exhaust.

Potential Dangers of Gas Coming Out of the Lawn Mower Exhaust

Potential Dangers of Gas Coming Out of the Lawn Mower Exhaust

Though it may seem harmless, gas coming out of your lawn mower’s exhaust can be quite dangerous. Here are 07 potential dangers to be aware of:

1. Inhaling gas fumes can be harmful to your lungs.

2. Gasoline is highly flammable, and a spark from the exhaust could ignite a fire.

3. If gas leaks onto the ground, it can pollute waterways and harm animals.

4. Leaking gas can also damage your lawn mower and other outdoor power equipment.

5. Gas fumes can cause headaches, dizziness, and nausea.

6. Prolonged exposure to gasoline fumes can lead to more serious health problems, such as liver damage or cancer.

7. Inhaling gas fumes while pregnant could harm your developing baby.

A Similar Topic: How do I know if my lawn mower has bad gas?

Prevention Steps to Avoid the Lawn Mower Smoke From Happening Again

Lawn mower smoke can be a nuisance, particularly when it happens regularly. Some prevention steps can be taken to prevent the smoke from happening again.

This will help to prevent the smoke from billowing out and affecting the surrounding area. It is important to make sure that the lawn mower is properly serviced and maintained. This will ensure that the engine is running smoothly and not producing excess smoke. 

Finally, keeping the lawn mower clean and free of debris is also a good idea. This will help reduce the amount of smoke produced when the lawn mower is in use. By following these simple prevention steps, it should be possible to avoid lawn mower smoke in the future.


1. Why Is My Lawn Mower Releasing White Smoke?

If you’ve ever started up your lawn mower only to have it release a cloud of white smoke, you may be wondering what’s going on. This could indicate that your engine is burning too much oil, which can damage the mower and cause an accident. 

One possible reason for this is that the mower’s air filter is dirty and needs to be replaced. Another possibility is that the mower’s spark plugs are fouled and need to be cleaned or replaced. If you’re not sure what the problem is, it’s best to take the mower to a qualified technician for diagnosis and repair.

2. What Is The Reason My Lawn Mower Is Emitting Black Smoke?

Black smoke coming from your lawn mower’s exhaust is never a good sign. In most cases, it indicates that the motor is overloaded, meaning that too much gasoline is burned. This can be caused by a number of things, such as a dirty air filter, an incorrect spark plug, or a clogged fuel line.

If you notice black smoke coming from your lawn mower’s exhaust, you should take it to a mechanic to have it checked out. It’s also important to make sure that you’re using the correct type of oil in your lawn mower. Using the wrong oil can cause black smoke to be released from the exhaust.

3. Do Electric Mowers Release smoke?

Electric lawn mowers are much cleaner and produce no smoke. This is not only better for the environment, but it also helps to keep your lawn and garden free of pollution. In addition, electric lawn mowers are much quieter than their gas-powered counterparts, making them ideal for use in residential areas.


The process is relatively straightforward. It’s easy and inexpensive to sort out your problems with your lawn mower. It is possible to circumvent this problem with careful preparation and good planning. 

Ensure that your lawn mower is protected from smears and will last for a long time. We hope the article on “why is gas coming out of my lawn mower exhaust” was useful to you, dear tool owners. Thanks for your patience in reading.