Smoking Lawn Mower: Causes and How to Fix It

For any homeowner who mows their lawn regularly, sooner or later they’ll notice smoke coming from their lawn mower. Naturally, this is an alarming thing to notice. But more often than not, a smoking lawn mower isn’t serious and the problem can be fixed pretty easily.

Of course, it’s important to find out what’s causing your mower to smoke. Knowing the cause will help you determine if it’s still safe to use. In today’s article I’ll explain the most common reasons why lawn mowers smoke. Then I’ll tell you how to fix the problem.

Let’s get to it!

Is a Smoking Lawn Mower a Big Problem?

Usually, when a lawn mower smokes the issue is minor and will go away on its own.

However, if it doesn’t resolve by itself, and occurs alongside an engine issue, it may be necessary to take your mower in for repair.

So how do you know if your mower has a big problem or a minor one?

The color of the smoke is the most important information that can help you learn what the issue is with your mower (and how to fix the problem).

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What Should You Have Before You Start

Before we dig into diagnosing the problem, here’s a few things you should have if you’re planning to fix your mower yourself:

• Owner’s Manual
• Cool Mower (don’t burn yourself)

Remember – before you start any repair on your mower, it’s important to consult the user manual for your specific lawn mower.

I know, I know – nobody likes to read the instructions. If you’ve owned your mower for a while you may not be able to find your user manual.

But seriously – take a minute to pull it up online. It’ll save you some time, and make fixing your mower much faster (and safer).

And finally, before you attempt to repair your mower’s engine, give it some time to cool off so you don’t burn yourself.

Go have a beer and make a PB&J. It’ll make the whole process go better if you’re fed and well lubricated.

Lawn Mower with Blue or White Smoke

Whenever blue smoke or white smoke billows from your lawn mower, it typically means the mower is burning oil that’s spilled onto the engine or into the combustion chamber.

What Causes Lawn Mower with Blue or White Smoke?

There are many reasons why this occurs, and it is most commonly because the oil has overflown.

If you:

• Tilted the Mower for Maintenance – Some mowers can leak oil if tilted on its side for maintenance.
• Mowed on Especially Hilly Terrain – If the mower was used on a 15-degree incline or more, it could leak oil in the same way.
• Recently Filled the Oil Resevoir – If too much oil was added, extra oil can leak and be burned.
• Recently Filled the Gas Tank – If you added too much gas when you filled your tank, some may have spilled on your motor, which will burn off.
• Bought a New Mower – Sometimes there’s leftover oil residue in new mowers, so if your brand new mower is smoking a bit, this could be why. Certified Horticulturist Nicole Forsyth, M.S. suggests that when you buy a new mower you plan to change the oil after 5 hours of use, saying “this will make sure all metal shards and such from fabrication of the mower are flushed out and not sitting and destroying the mower engine internally.”

Typically, these issues take care of themselves, and you’ll notice that your mower will stop smoking in 15 minutes or less.

If you just added oil and think you overfilled it, it’s easy to check. Once the mower has cooled, remove the oil dipstick, wipe it, and reinsert it to get an accurate level.

When Blue or White Smoke is a Bigger Issue

If the smoke persists after 15 minutes of running your mower, it’s likely that you have a bigger issue with the engine.

This could mean the seals on the combustion chamber have worn and oil is leaking into it.

My best guess is that either there is an air leak in the crank case or that the cylinder and rings are worn.

It could also be an issue with the head gasket, meaning it’s either blown or needs to be cleaned. These issues will likely need professional maintenance by a small engine repair service. Damage to the cylinder and piston rings can also create a leak.

If the issues still continue beyond your repairs, it could indicate a serious mechanical issue with the mower.

What to Do Next

But before you panic, check if your mower is still under warranty to be repaired at the nearest servicing dealer. Any issue relating to a factory defect or poor workmanship might have its repairs covered with no cost to you, and some of the major lawn mower brands will make it right for you in some way.

If you don’t have luck with a warranty claim, a reputable small engine repair company will be more than capable of making all the necessary repairs. If you have a good mower, this may be cheaper and a wiser use of money than buying a new mower.

Lawn Mower with Black Smoke

When there’s black smoke coming from your mower, it’s because the fuel and air mixture are not balanced.

The mixture is too rich, and the fuel isn’t getting enough air to complete combustion. The unburnt fuel in the combustion chamber turns to smoke because of the lack of air circulation.

Quick Fix to Lawn Mower with Black Smoke

Black smoke is most likely because the air filter is dirty, which is an easy fix.

With a push mower, your air filter is probably located on the side of the mower. It’s usually in a plastic box that’s screwed or clipped into place.

If you have a foam filter in your mower, it can be removed and cleaned with soap and water. Paper filters can be cleaned with a vacuum or compressed air.

Some filters are disposable and need to be replaced with a new filter. I replace mine annually as part of my spring mower maintenance routine.

Make sure there are no obstructions in the breather tube, which is located behind the filter. This and the muffler can also clog if the filter is dirty.

After removing the filter, use a wire brush to clean inside the pipe. After cleaning and replacing the filter, start the mower back up and let it run.

If the Air Filter Isn’t Causing Black Smoke

If your mower starts back up, but black smoke persists, adjust the carburetor to make a leaner fuel mixture.

You can have this done at a small engine repair service. You can do it yourself by removing the carb and turning a screw (usually). Consult the owner’s manual for more specific directions with your mower.

If Your Black Smoking Lawn Mower Won’t Start

If your mower smokes black and then isn’t starting, there’s more going on then an air filter or carburetor issue.

When the engine doesn’t start, check the spark plug. Either cleaning or replacing it will likely fix the issue. This is a job anyone can do with the right wrench.

Use a socket wrench to unscrew the plug. If you observe thick deposits on the plug, that’s likely to source of the issue. Remove it using sandpaper or a file. Or just replace the spark plug (it’ll cost about $8.50 at your local box store).

Nicole Forsyth, a member of our expert panel, adds that homeowners should “make sure you use the proper spark plug socket which has a rubber fitting inside to not break the fragile ceramic plug.”

Why this Fix Works

A mower that produces a lot of black smoke has issues running at full power. The smoke creates a carbon build up in the engine. After a significant period of buildup, the carbon buildup prevents the spark plug from starting the ignition. This is why you can get the engine running after cleaning or replacing the spark plug.

Now You Know How to Fix a Smoking Lawn Mower

It’s frightening whenever your mower starts to smoke, but more often than not, smoke will clear on its own.

Usually it’s because of an oil leak or spill, or a dirty air filter, though if the fixes detailed in this article don’t solve the problem, you may have bigger concerns or more persistent issues.

Hopefully these solutions help you get your mower to stop smoking, but if the problem persists, there’s no shame in getting an opinion from a professional small engine repair service.

It’s generally a lot more affordable than buying a new mower.