How to Stop a Lawn Mower from Smoking?

In Brief: How to Stop a Lawn Mower from Smoking

Grey smoke from a lawn mower engine is usually caused by problems with the oil. Start by checking the oil levels, changing the oil, or flushing the system. Next, check the fuel filter and the crankcase. If the mower is producing black smoke, it’s more likely a fuel issue. Spray carb cleaner first or try replacing the air filter.

Although the engine on a gas lawn mower is small, it can have a variety of issues in any of the systems. If your mower is smoking, whether it’s a little bit or a lot, there are steps you can take to fix it yourself.

Here, you’ll learn how to stop a lawn mower from smoking by addressing some of the most common causes. If you try the solutions here and your mower is still smoking, you may need to visit a repair shop.

6 Ways to Stop a Lawn Mower from Smoking

Lawn mowers smoke for many different reasons. Smoke is a symptom that indicates a problem but doesn’t show you the exact issue until you look closer. There’s often a simple solution to a smoking mower that you can fix easily at home.

The very first thing you want to do is identify the type of smoke you’re seeing. Based on the color of the smoke coming out of the mower, you can narrow the list of problems down.

Here are 6 ways to stop a lawn mower from smoking, based on the color of the smoke coming out of the engine.

Watch this quick overview of some of the most common problems:

Fixing White or Bluish-Grey Smoke

When the smoke coming from your mower is white, bluish, or light grey, you are more likely to have a problem with the oil.

Method 1: Engine Oil Fixes

A number of different problems with the engine oil can cause white, bluish, or light grey smoke. The first and simplest thing to check is the oil level.

When the engine oil is overfilled, it can cause a large amount of smoke to spew out of the mower.

You might also notice oil spitting out of different parts of the engine. Remove the dipstick to check the oil levels. If it’s overfull, empty the oil and refill it to the correct amount.

Another common problem with engine oil is using the wrong type. Check the manufacturer recommendations for oil grades and types. Only use the oil recommended by your manufacturer or a direct substitute.

Lastly, oil might leak if you tilt your lawn mower for any reason, or if there are any leaks within the engine.

If the first two oil problems don’t solve the smoke issue, check for signs of oil leaks. Usually leaks are caused by tilting the mower onto the wrong side, or by worn our seals and O-rings.

Method 2: Fuel Filter Replacement

An old or clogged fuel filter can cause smoke to come out of your mower. If your mower has a fuel filter, it should be located along the fuel intake line leading to the carburetor.

By removing the carburetor cover and air filter, you should be able to access the fuel intake line on most mowers.

Check the fuel filter by looking for visible debris. If you hold up the filter to a light and you can’t clearly see the light through it, you should change the filter. Here’s a simple guide to changing your fuel filter:

Method 3: Crankcase Maintenance

The crankcase helps to remove fumes from the mower’s engine. If crankcase oil has impurities or sludge buildup, this can cause it to smoke. An oil flush helps remove any buildups around the engine.

Pour an oil solvent agent into the oil fill valve. The manufacturer specifications should say how much to use. Turn the mower on and leave it running for 3-5 minutes so the oil and solvent can move around the entire engine.

Once you’ve left it running for a few minutes, turn it off again and drain the oil and solvent mix. Refill the mower with clean oil.

Fixing Black or Dark Grey Smoke

Black or very dark smoke points toward problems in the fuel mixture or the engine burning oil. There are a few ways to diagnose and correct these issues, if the first 3 solutions were not effective.

Method 4: Carburetor Cleaning

Lawn mowers run on a fine mix of gasoline and filtered air. If the balance of gas and air is disturbed, it can result in smoke coming out of the mower. Because the carburetor is responsible for mixing the right ratio, it’s the first place you should check for problems.

First, try spraying carb cleaner onto the carburetor. You should be able to see the carburetor underneath the air filter. Spray the carb cleaner thoroughly onto the carburetor and let it sit for a few minutes before testing it again.

If carb cleaner doesn’t solve the problem, you may need to remove and clean the carburetor. This is a more complex process detailed here.

Method 5: Air Filter Replacement

Other than the carburetor, the air filter is the other piece involved in mixing the fuel and air ratio. If the air filter is clogged, there may not be enough air getting into the carburetor. Check to air filter to make sure it’s clean and free of debris.

If it looks dirty or shows visible clogs from debris, oil, or something else, you need to clean or replace it. Foam air filters can be cleaned, oiled, and replaced. Paper air filters cannot be cleaned and need to be replaced.

Method 6: Breather Tube & Crankcase Replacement

Sometimes black smoke shooting out of the engine is a sign that the engine is burning oil inside the crankcase. This is usually caused by a broken breather tube that’s allowing oil to leak out of the crankcase.

When this happens, you’ll need to replace the breather tube.

If the crankcase is also broken in any way, you’ll need a new crankcase as well. Both the crankcase and breather tube are specific to certain types of mowers, so check to see which one you’ll need before you buy a replacement.

In many common mower brands, the breather tube and crankcase are located just below the muffler. The breather tube will be visible from the outside of the mower because of its function as a vent.

A visual inspection should reveal any warping, cracks, or otherwise damaged areas of either part.


Because there are so many things that can cause a mower to produce smoke, you should start with the simplest problems first. Check the oil levels, change or flush the oil, and clean or replace the air filter before you look at more complex solutions.

Give these methods a try! If you run into any problems or you have additional questions, leave a message in the comments.

About Linda Johnson

Linda has been working with power tools since she was 13 years old. As DIYer she works on wood and metal to develop artworks that she puts on sale. She loves traveling.

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