Lawn Mower Blowing Black Smoke (Why How to Fix)
If you’re out cutting the grass, the last thing you want is to send up a smoke signal letting everybody know that something is wrong with your lawn mower. Still, you can’t always prevent it. Smoke coming from your lawn mower is a telltale sign that something is going (or has gone) wrong. Mowers can produce either white/bluish smoke or black smoke. If your lawn mower is blowing black smoke, there are usually just a few major reasons for it.
Why is My Lawn Mower Blowing Black Smoke?
A lawn mower blowing black smoke means that the engine is running rich and is usually caused by the choke set/stuck “on”, a blocked air filter, or a carburetor that isn’t working correctly. Combustion engines depend on a mixture of fuel and air, and when there is too much fuel in the mix, it is considered rich (when there is too little fuel in the mixture it is considered lean).
Let’s take a look at each reason why your engine could be getting a rich mixture resulting in your lawn mower blowing black smoke.
Choke Set or Stuck “On”
Lawn mowers use either a choke or primer bulb to help get them started when the engine is cold. The choke on your lawn mower is used to enrich the gas and air mixture that the engine gets when first starting the mower. It’s called choking because the fuel/air mix is enriched by restricting the amount of air that can enter the carburetor. A primer bulb enriches the fuel/air mix by pushing extra fuel into the engine. Once the engine is running or warmed up a bit, the choke should be turned off. If it isn’t turned off, or it gets stuck on, the rich fuel and air mix will produce black smoke.
Only manual and automatic chokes can cause black smoke, primer bulbs will not. Double-check that your choke setting isn’t the issue first. If it isn’t, then run the mower and see if changing the choke settings affect how the lawn mower runs. If the choke seems to be working correctly, you’ll have to look into the air filter or carburetor.
Blocked Air Filter
Your mower’s air filter is super important and something that should be checked and cleaned off a couple of times a season. Technically it’s recommended that you clean your air filter every 25 hours of operation, and replace it every 100 hours. If your air filter is overly dirty or wet it can block air from getting to the engine. This is another way that you can end up with a rich fuel and air mixture creating black smoke. Luckily, it’s pretty easy to get at your air filter on most lawn mowers.
To tell if this is your problem, take a look at the air filter and if it has a bunch of dust or debris on it, try and clean it off. If it is wet or oily you should probably replace it. Then, once you have your cleaned or new air filter reinstalled, run the mower and see if the black smoke clears. Some people recommend taking the filter off and running the mower without an air filter to see if it’s the problem, but I wouldn’t advise doing that. It’s an easy way to suck a bunch of gunk into your carburetor or engine.
This usually isn’t the case but if you know that your choke and air filter are working correctly, the cause of your black smoke is probably due to the carburetor not working properly. The job of the carburetor is to mix fuel and air and shoot it into the engine. If the fuel and air aren’t being combined in the right ratio, the engine won’t run as it should. In the case of black smoke, the carburetor isn’t supplying enough air.
How to Fix a Lawn Mower Blowing Black Smoke
Fixing a lawn mower blowing black smoke means bringing the air and fuel mixture that the engine burns back into balance. Each of the three causes of a rich fuel mix has a different fix, so let’s check them out.
Choke Set or Stuck “On”
If your lawn mower has a manual (lever) choke, fixing the choke may be as simple as turning the choke off when the mower is running. But if that doesn’t work, or you have an automatic choke, you’ll need to dig a bit deeper.
Adjust the choke when the mower is running to see if it changes how the engine runs. Turning the choke off should make the engine run smoothly (and without black smoke) and leaving the choke on should cause the engine to run roughly. If the choke doesn’t seem to work as it should, you will have to adjust the cables that control the choke flap opening and closing. This isn’t a super complicated job but usually requires the removal of the carburetor.
If you have a newer lawn mower, it could have an automatic choke. These adjust themselves using a thermometer reading. As the engine warms, the thermometer should force the choke flap to open (turning it off). If it isn’t working properly it is usually because the thermometer is broken, or the links attached to the choke flap aren’t allowing it to open and close. Replacing these parts can be a bit more tricky than dealing with a manual choke.
Blocked Air Filter
Cleaning off your filter can be done relatively easily. Usually, there is just a plastic clip or a set of wingnuts or small bolts holding the filter in place. Blowing off the air filter with compressed air, or tapping it down on a clean surface will usually shake off any loose dirt or debris.
But if the filter has gotten wet or soaked up any oil, you’ll need to replace it. The part isn’t expensive, and installing a new filter just requires reversing the steps you take to remove it. It’s worth maintaining a clean air filter because it will help your mower in more ways than one.
Again, if the choke is turned off, and the air filter is clean, the carburetor is now your prime suspect. Fixing a carburetor that is mixing too much air in means two things: adjusting the airscrews, or replacing the carburetor. The airscrews on carburetors are always screwed in a precise amount to control the air intake. You’ll need to reference a service manual or manufacturer’s specifications to determine how far the screw should be set. Usually, you need to turn the screw all the way and then back it out a set number of turns.
If you go through the trouble of removing the carburetor and find that the screw was already set correctly, you will have to replace the carburetor. Depending on what type of lawn mower you have, it shouldn’t be too costly to do yourself. If you don’t have the tools or know-how to tear into your carburetor, you should have a small engine mechanic tackle the project for you.
Why is My Riding Lawn Mower Blowing Black Smoke?
Riding lawn mowers blowing black smoke do so for the exact same reason that push mowers do: a rich fuel and air mixture. Check the choke, and air filter first to see that they are functioning as they should. If they are, you will have to check for carburetor malfunctions.
Causes of 4 Stroke Lawn Mower Blowing Black Smoke
Unlike a lawn mower blowing white or blue smoke, 4-stroke and 2-stroke mowers blow black smoke for the same reasons. The type of choke is essentially the only thing that will differ between push mowers. Again, if your mower has a primer bulb, the choke is not the issue and you’ll need to look at the air filter or carburetor.
Causes of 2 Stroke Lawn Mower Blowing Black Smoke
As I mentioned in the section above, a 2-stroke mower will blow black smoke for the same reason as a 4-stroke mower. Because black smoke is related to the fuel and air mixture, all lawn mowers produce black smoke for the same reasons. But, to be clear, this isn’t always the case for white or blue smoke.
Is Black Smoke from Lawn Mower Dangerous?
Black smoke from a lawn mower isn’t only bad to look at, it can actually be dangerous for a number of reasons. First off, black smoke is basically just soot from unburned gas/fuel being pushed out through the exhaust. If inhaling gas fumes is bad for you, you definitely don’t want to breathe in a bunch of sooty fuel that has run through your engine. Also, black smoke coming from your lawn mower can signal damage occurring within the mower. A lawn mower burning a rich fuel/air mixture can lead to you needing to replace choke parts, an air filter, spark plugs, or even the carburetor itself. If you see black smoke, be sure to address the problem right away.
About Tom Greene
I’ve always had a keen interest in lawn care as long as I can remember. Friends used to call me the “lawn mower guru” (hence the site name), but I’m anything but. I just enjoy cutting my lawn and spending time outdoors. I also love the well-deserved doughnuts and coffee afterward!
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Why Does My John Deere Smoke? [Causes Solutions]
You’re bound to get some anxiety when you notice smoke spewing from the exhaust or elsewhere on your expensive John Deere Mower. How bad is it? How much is it going to cost to get it fixed? Is the damage permanent? These are all reasonable questions, but there’s no reason to panic.
There are several potential causes behind smoke pouring out of your John Deere. Low coolant levels, low engine oil levels, too much oil, bad injectors, plugged air filters, and leaking head gaskets are some of the most common reasons for a smoking John Deere.
Fortunately, all of the above is repairable, and although a leaky head gasket sounds complicated, it’s not as bad as you think, and it’s also one of the rare causes on the list.
There are also cases where there may be white smoke, and nothing is wrong with your mower.
Potential Causes and Solutions
Nobody wants to see smoke spewing out of their lawnmower, especially if it’s a new John Deere, but it happens. So, the next step is ascertaining the problem. Where it’s coming from and how to fix it, hopefully on your own.
DIY repairs are the best way to go if you have the tools and capacity, especially when it comes to a John Deere because they don’t just hand out repairs for free.
However, if you have it under warranty, that’s a different story. Warranty or not, what could be the source of the smoke?
Low Coolant Level
Low coolant levels are easy to ascertain as you can simply check your coolant level and ensure that it is where it’s supposed to be. Of course, you want to let your mower cool down before you pop the cap.
When the coolant gets too low, overheating occurs throughout the engine, and while it won’t smoke like crazy, you will see some white smoke coming from the engine. If you own a relatively new John Deere, there’s a chance that you have low coolant because there is a slow leak somewhere.
You should top your coolant off, but you should check all of the connections in and around your radiator and observe it carefully while it is running.
There are three things required for combustion: air, fuel, and spark. If your engine isn’t getting enough air, then it is probably running “rich,” a term for too much fuel and not enough air for proper combustion. This will cause black smoke rather than white, and one of the first suspects is the air filter.
You should remove it and clean it thoroughly (use compresses air to blow it down if you can), but you should also include your air filter in your routine maintenance procedures.
Oil Level is Too High or Too Low
Lack of lubrication will certainly produce smoke, as you will have an increase in friction and heat from moving parts within the engine that are not properly lubricated.
The problem with low oil levels is that by the time you notice it (thanks to all of the smoke), there will likely be side effects throughout the engine.
Also, like the coolant levels, if your John Deere is relatively new or well taken care of, a low oil level is likely a sign of a leak somewhere.
Too much engine oil is nearly as problematic as the reverse. Excess oil burns off and increases pressure in the crankcase. The burning off creates smoke and, as a side effect, will damage or clog your air filter as well.
You’ll need to drain the oil and change or clean the air filter. Whenever you put oil in the mower, always use only the recommended oil type and the exact amount specified in the user manual.
If your injectors aren’t working correctly, you will not get the right amount of fuel. This usually leads to fuel that isn’t burned away and leftover fuel that isn’t ignited. The typical result is white smoke. However, the John Deere will also show signs of sluggishness, vibration, or otherwise just not running right.
Depending on what John Deere you have, the process for changing the fuel injectors can be drastically different. Fortunately, there are a lot of YouTube videos on the process. Also, if your John Deere is under warranty, you will want to take it in rather than risk voiding the warranty trying to repair it yourself.
There are also several fuel injector cleaners you can try first, as that might be enough to resolve the problem without having to get it repaired.
Leaky Head Gasket
If your John Deere is pretty new, a leaky head gasket is undoubtedly something that will be covered under warranty, so long as you haven’t done anything that would directly cause damage to a head gasket.
This is probably one of the more difficult things when it comes to a DIY fix, so if you are not a John Deere Tractor or Mower mechanic, it might save you a lot of headaches to just take it in for a repair.
It may be on the expensive side, but it’s not as bad as purchasing a new John Deere.
White Smoke, Black Smoke, and Blue Smoke
White, black, or blue smoke might not tell you exactly what the problem is, but they will point you in the right direction if you know what they mean.
Black smoke is usually caused by burning too much fuel without enough air. Most of the time, that indicates bad injectors or, more commonly, a clogged-up air filter. If your air filter is relatively clean, there is an air restriction somewhere, which might be a problem with the choke.
Blue smoke is usually the direct result of burning oil. It’sIt’s just the color that tends to come from it when it is burning rather than lubricating the moving parts throughout your engine. Sometimes, the blue can be really dark, and that might mean that you have multiple issues going on.
If you see blue smoke, check your oil levels to ensure that the reservoir wasn’t overfilled during your last oil change or that there is plenty of oil there.
It’s mostly going to be a problem from excess oil. However, leaking oil can find its way into places hot enough to burn it off, and you’ll notice a low oil level.
You get white smoke from leaky head gaskets and gas in the oil or vice versa. Diesel engines are more prone to white smoke, but that doesn’t mean you will never see it in gasoline engines.
Diesel fuel filters that aren’t working properly can cause white smoke, and out of three colors of smoke, this one will be the most prevalent, especially in diesel engines.
Signs of smoke emanating from your John Deere aren’t the end of the world. However, there is always cause for concern.
The best thing to do is address the smoke immediately and locate the cause, even if you discover that the cause is nothing damaging.
- Why Does John Deere Use Yanmar Engines?
- Are John Deere Tractors Worth The Extra Money?
- Why Are John Deere Mowers So Expensive?
- Is A John Deere Gator Considered An ATV?
- Why Does My John Deere Gator Grind When I Put It In Gear?
- Can I Use Synthetic Oil In My John Deere Riding Lawn Mower?
Yard Troop is owned and operated by a project lover and is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. Susan also participates in affiliate programs with Bluehost, Clickbank, CJ, ShareASale, and other sites. Susan is compensated for referring traffic and business to these companies.
I love working in the yard and coming up with projects around the house. In addition, I am blogger. I’ve decided to start this blog to share stuff I learn about yard work, or any projects that are house related. These days I blog about everything related to anything pertaining to the outside of the home. Everything in this blog should be used for educational purposes only.
Why is My Lawn Mower Smoking – 5 Reasons Why!
Mowing your grass can bring great pleasure to us lawn connoisseurs and is a great way to keep your yard looking neat and tidy. It can be frustrating when your mower might not want to keep up its end of the deal, though, and especially you start seeing smoke.
Why is my lawn mower smoking you ask? Here are five common reasons why.
Why is My Lawn Mower Smoking?
The wrong fuel type
There are three types of push mower motors available for everyday folk to purchase; Electric motors, two-stroke, and four-stroke.
Two-stroke and 4-stroke are the two combustion engine types. Here’s a quick explanation of the difference between the two. So why is my lawn mower smoking?
Because the engines work in different ways, they require slightly different fuels.
- 2-stroke engines need their oil mixed into the fuel to keep the motor lubricated.
- 4.stroke engines get their oil from a separate reservoir in the mower, and they run on regular unleaded fuel.
If you use a 2-stroke oil and fuel mix in your 4-stroke engine, there will be too much oil during combustion, and your mower can billow with smoke.
If you use regular unleaded fuel in your 2-stroke engine, there’s no oil present, which causes your engine to struggle, strain, and seize.
You can also get too much oil in your fuel if you use the wrong ratio when mixing your 2-stroke fuel.
As a side note, electric motors should never smoke unless something catastrophic has happened. You should immediately stop work and take your electric mower to a repair shop if you see any smoke when using one.
Fuel and oil getting onto your mower
Another possible reason why your lawn mower is smoking again comes back to fuel and oil.
When filling your mower with fuel or oil, make sure you don’t spill any. Not only will spilled fuel kill grass, or stain anything it’s spilled on, it also runs the risk of igniting when your engine gets hot.
If you’ve ever seen fuel or oil on fire, you’ll know that it’s a smoky affair.
If you do happen to spill anything when refueling, wipe it off as best you can with a rag. Always give your mower a visual check over before mowing to check for any leaking fuel or oil as well.
Built-up grass is burning
Depending on where you live, dry grass and leaves that get caught up in between the engine and the body of your mower can catch fire and begin to smoke.
While not a common scenario, it can be a reason why your lawn mower is smoking.
Dry organic matter that is pressed hard against a hot combustion engine can begin to smolder and smoke as you push your mower along. If it catches fire it can cause grease and oil on your mower to ignite. This can then even begin to melt any plastic parts of your mower.
To help stop this, always wash or blow down your mower after use. Having a nice lush green lawn, and avoiding mowing on hot dry days can also help stop this from happening.
Dirty air filters.
Your combustion engines run by igniting a fuel and air mixture via the spark plug to make the motor turn your mower blades. But why is my lawn mowing smoking?
Oxygen gets into the combustion chamber through air-intakes in your mower. The engine sucks in air for use in combustion as it turns over. Air intake inlets are covered by air filters, which stop dust and grit from getting inside the engine and causing damage.
If your air filter is dirty and is becoming blocked, your engine won’t get enough air, and the air-fuel mix with be too rich with fuel. This will mean that the fuel won’t burn properly. Too much fuel in your mix will cause the engine to begin to smoke, and eventually, it will stop running.
You can help solve this by removing and cleaning your air filter regularly. You can also have your mower serviced by a mechanic every year.
If you’d rather keep it to DIY, you can easily find replacement air filters for your mower.
Obviously, smoking mowers can be from something more serious and harder to fix than just some poor fuel or a bad air filter.
Internal components of your mower that become worn or damaged over time can have smoking as a symptom.
Damaged piston rings, carburetors, exhausts, or head gaskets can all cause smoke to waft out of your mower.
Unless you’re a mechanic, a lot of these issues will need professional repair. To help avoid your mower getting to this point it’s important to do proper lawn mower maintenance. It also really pays to get your machines serviced by a professional regularly.
Summing it all up.
If your asking yourself the question “Why is my lawn mower smoking” consider these five things.
Make sure you’re using the correct fuel for your mower. Two-stroke engines need fuel with oil mixed in. Four-stroke mowers need regular unleaded but need their oil added to a separate reservoir.
Check that your two-stroke fuel blend is the correct ratio for your mower.
When filling up your fuel or your oil, make sure you clean up any spills so that they can’t ignite and smoke while you’re mowing.
Clean your mower after each cut to make sure no caught grass can dry out and build up in the nooks and crannies of your mower body. If these get stuck against a hot part of the engine, they can begin to smolder or even catch fire.
Have your air filter checked, cleaned, and replaced regularly to ensure that the engine can get the correct airflow for proper ignition. Blocked air filters will cause your engine to sputter, smoke and stall.
Get your mower regularly serviced to keep on top of any issues before they become serious.
Internal problems like worn rings and seals, damaged carburetors, and exhausts can cause smoking.
So over to you? Do you have any other reason why your mower might be smoking? Let us know below!
Posted on Published: March 5, 2022. Last updated: April 5, 2023
Why Your Lawn Mower is Smoking (Black, Blue or White Smoke)
The first thing you should do when you notice smoke coming from your mower is to stop the engine to avoid potential engine damage.
A lawn mower is smoking due to a plugged air filter, low engine oil, too much engine oil, a bad engine gasket, a blown seal, an oil spill, or problems with the valve train or piston ring.
You should start with the simple items to check before moving on to the more complicated diagnostics. Wait for the engine to cool and remove the spark plug boot(s) before making repairs.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
Reasons a Lawn Mower is Smoking (Black, Blue or White Smoke)
Clogged Air Filter
If my engine was smoking the first Item I would check is the air filter system. This is the easiest thing to check so why not start there?
- First, remove the air filter cover. The cover is always located above the carburetor so that it can pull in clean air. Depending on the type of mower you have, the cover usually has a single screw or two knobs holding it down.
- Some air filters will be along the side of the engine next to the carburetor.
- Pull the filter out being very careful not to let any dirt fall into the intake pipe when you remove the filter.
- Inspect the filter and check to see if it is full of dirt and grass. If it is, the engine will not be able to breathe. Instead of pulling in the fresh air, a clogged filter will bring in air from the engine crankcase or the internal part of the mower engine.
Insufficient Engine Oil Level
If the air filter is not the problem, the next thing you are going to check is the engine oil. Now you may be asking yourself why you are checking the oil. If your engine oil is lower or higher than the manufacturer’s recommended oil level it can result in a smoking lawn mower.
Low Engine Oil Level
If your engine oil is low, you could be burning up the engine due to extreme heat causing lawn mower engine to smoke. In this case, the engine is having a meltdown and burning up the small parts in the engine.
You can try to add fresh oil to see if the smoking stops, but most of the time, at this stage, it is often too late for this simple solution.
High Engine Oil Level
Having too much oil can cause too much crankcase pressure which causes oil to get back into the cylinder or even up to the air intake through the valve train.
In this case, the oil is getting into the cylinder and begins to burn off when the engine is running at full speed creating smoke. You need to drain some oil out of the engine to resolve this problem.
Piston Ring Problem
After checking the easier troubleshooting steps and not finding any problem with the air filter or oil level, the next thing to do is check for oil on the spark plug. To do this, you will need a socket to remove the spark plug.
You may need a 3/4″ or 5/8″ socket to remove the plug. Inspecting the plug isn’t going to tell us a lot about the type of engine problem you have but pulling out the spark plug and checking to see if there is excessive oil buildup on it indicates you have a larger internal engine problem.
If you are mechanically inclined, you could check for internal engine damage. I recommend bringing your mower to a small engine dealer repair shop if you are not. If you find a lot of oil on the spark plug you may have a piston ring or valve train problem.
Either problem will result in you having to take the engine apart. A spark plug with oil build-up can indicate there is a ring problem and a score inside the cylinder wall.
If the cylinder has a score in it, the engine can bring up the oil to the combustion chamber and begin burning it.
This will create your lawn mower to begin smoking while in use. You may have to replace the engine in this situation.
Valve Train Problem
Sometimes having a valve train problem is not that bad of a problem to have. The only way to detect this is by removing the cylinder head or performing a leak-down test. This should be completed by a small engine mechanic.
The cause of a valve train problem is the result of the valve getting burned by being overheated. The edges of the valve begin to fall apart due to the heat. This is what is often referred to as a burnt valve.
You can also see a burnt valve or timing problem if the muffler is glowing red from heat while the engine is running. In this case, you will need to replace the valve and grind the seat.
The seat is where the valve contacts the engine block to complete the combustion chamber.
Both the valve and the seat will have to be cut at certain angles in order to make the valve seat correctly.
Bad Mower Engine Gasket
A bad engine gasket may leak oil onto the muffler and make the lawn mower engine smoke as it burns. You will need to find the bad gasket and replace it.
This may sound easier than it actually is. It becomes increasingly more difficult depending on the location of the bad gasket.
Difference Between White, Blue and Black Mower Smoke
Sometimes the color of the smoke can give you an idea of what kind of engine problem you are dealing with. It is best to go through the checklist above to narrow down the issue, but here is a quick list of items that could be causing the smoke.
Blowing Black Smoke
This color usually is due to the engine running too rich. The ratio of fuel to air is incorrect with more fuel being burned than air.
If you see black smoke coming from the mower, the first thing to check is the air filter. A plugged air filter must be cleaned or replaced. If the filter isn’t the issue check for another air flow restriction.
Blowing Blue or White Smoke
This color smoke is due to burning excess oil. It is best to follow the steps above to identify the root cause starting with checking the engine oil level followed by checking for damage to the piston rings, valve train, or engine gasket.
It is essential to continue to check your engine oil level and air filter before each mowing use to avoid large expensive repairs. For a checklist to perform before each mowing, I explain it in my Lawn Mower Checklist.
Complete Regular Engine Oil Changes
It may seem like a lot of work to change your engine oil, but changing your oil is necessary. To keep your lawn mower running and not shorten the life of the mower’s engine, you must change the engine oil regularly.
Read more about the damaging effects of skipping your oil change, Engine Damage is Likely if You Skip Mower Oil Changes.
Still Having Problems with Your Lawn Mower?
Lawn mower ownership doesn’t come without its frustrations. Own a mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting, and overheating.
For mower troubleshooting, check out my guide Common Lawn Mower Problems: Solved.
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