Why Your Lawn Mower Blows Blue Smoke.
It’s a beautiful day and you head outside to mow the lawn. Probably thinking that you could be doing better things. This feeling is compounded when you start to see smoke rising from your mower. Although this is annoying it pays to do a few simple checks before running off to the local fix-it shop.
There are a few things that can make your mower smoke and although it may appear to be something major it is normally a simple fix.
A lawnmower blows blue, white or black smoke for the following reasons.
- oil reservoir has been overfilled.
- The mower has been tipped on its side.
- Choke needs adjustment.
- The air filter is blocked.
- The carburettor needs adjusting.
- The spark plug gap is wrong.
- The engine is worn.
The colour of the smoke is a clue about the problem and in my 30 years of commercial lawn mowing I have encountered all of them.
This is a simple list I would give to my employees to go through before they contacted me. If you run through this simple checklist you should be able to self-diagnose the problem, fix it, and get back to that lawn.
The mower blows out Blue or White smoke.
This is a sign that the engine is burning excess oil. The excess oil in the engine causes incomplete combustion which will create smoke and a carbon buildup. The engine may run like this for a while but eventually, it will foul up and become increasingly hard to use and eventually die.
Has the oil reservoir been overfilled?
The first thing you should do is check your dipstick. If you cannot find a dipstick then you have a two-stroke engine go to the bottom of this post and I talk about two strokes there.
If the oil is above the maximum full lever on your dipstick then is a problem. You will need to drain some oil out of the mower. There are a few ways to do this.
- Unbolt the sump plug. This is usually the engine manufactures recommendation. A word of warning here. Not all engines have a sump plug so if you cannot find it go to step two. Remember to access under the mower by lifting the front wheels up, not by flipping the mower on its side. (you don’t want to compound the problem). In most cases, you will need to remove the blades.
- Remove the dipstick and tip the mower on that side. I know that in step one I said don’t tip the mower, but it is ok if the dipstick is removed. As long as you do not tip the mower on the filter side you will be fine. It is a good idea to run the mower for a few minutes first (this makes the oil flow better). Drain out a bit of oil and check the level again. Do this until it is on the right level on the dipstick and then run the mower for about five minutes until the smoke clears.
- Use an oil extractor pump. This is the tool that most mower shops will use. I would suggest method two but if you are going to be doing this a lot then an oil extractor may come in handy in the future. This is a good one made by Briggs Stratton on Amazon. Again run the engine for a few minutes before draining the oil.
If you are not sure how to use an extractor pump then the Briggs and Stratton website has a video that walks you through this procedure.
Do remember that if your mower was smoking you have probably fouled up the spark plug as well. You will need to clean or replace it.
Finding the sump plug.
Has the mower been tipped on its side?
If your mower has been tipped on its side then this could be the problem.
This can happen if you flip the mower without thinking if something tangles up on the blade or cleans under the mower. It is even possible for this to happen when you are mowing on a slope if the angle is great enough. This is more likely when you are mowing across a steep lawn rather than up and down.
If you flipped the mower with the muffler side towards the ground then you may have got oil in the muffler. Provided it wasn’t left like that for too long this should burn off. Let to mower idle for five minutes and see if it clears up.
If you tipped it on the air filter side then that is not as easy. First, check your air filter. If it is full of oil you are going to have to clean out the holder and replace the air filter. If you do not have access to an air filter immediately don’t worry too much, the mower will run ok without it while you finish the job. Just make sure to replace it before you use the mower again.
Now top up your oil, clean or replace the plug and you should be good to go.
Is the choke working correctly?
Check the cable attached to the on/off switch. Make sure it is not sticking in the choke position. This can cause too much fuel to get through which will create smoke and a badly running engine. Spray the top and bottom cable with Lubricating Oil and work the on-off lever.
Check to see if this has solved the problem.
If this does not solve the issue or you have an automatic choke then you will need to get this checked at your local mower shop.
Ware and tear on the engine.
If you can find none of the causes above it may be the engine and you will need a compression test.
This could be any excessive wear on the engine but it is usually a worn cylinder, rings, or the sign of a blown head gasket. All of these things will need to be done by an experienced mechanic so do not attempt to fix this unless you know what you are doing.
The mower blows out black smoke.
This is caused by the engine burning more fuel than air. Too much air leads to partial combustion and the excess fuel can turn into smoke.
The air filter may be blocked.
Pull off the air filter. Clean it by tapping it on the ground or by using an air compressor. Clean out the housing and replace the filter if it is too far gone. To test simply pull the filter out and start the mower. If the mower starts and doesn’t smoke then it is the filter.
If you have a foam air filter then you could wash it in warm water with a few drops of dishwashing liquid. Wring the water out and leave it to dry naturally. When dry I put it in a plastic bag with a little bit of Foam air filter oil then I squeeze the bag to evenly distribute the oil. This last step is not necessary but I prefer doing it as it catches dust better, especially if you work in dusty environments.
Your air mix on your carburettor needs adjusting.
This is normally a screw that you can adjust on your carburettor called the idle adjustment. You can turn the screw and it will adjust the idle on your engine. You can slow the engine down if it is idling too fast or vice visa.
How to Adjust your carburettor video
I normally just throw a new plug into the mower if I have any problems. This is the first thing a mower shop does when you bring a lawnmower in. They are only a few dollars each so its always worth having one on hand.
A Faulty crankcase breather.
If you have ruled out everything else excessive oil consumption and smoke can be the sign of a blocked crankcase breather.
Unless you are handy with engines then you would probably want your local mower shop to do this.
Two-stroke engines blowing smoke.
The first thing you would want to check with a two-stroke engine is that you have used the correct two-stroke oil at the right mix. If the oil mix is too heavy then it will cause the engine to smoke.
You do not want to just add petrol to dilute the mix because if you dilute the mix too much you will risk seizing the engine which is even worse.
You can check that you have the correct oil easily enough but there is no easy way to check the mix in your tank. I always say “if in doubt then throw it out” better safe than sorry.
There is normally a small fuel hose that attaches underneath the tank held on by a butterfly clip. Unclip that and drain your tank. Reattach it and put it in the correct oil/gas mix. If the engine stops smoking then you have found the problem.
If there is still smoking go through the list above starting at “Is the choke working correctly?”
Nobody likes a smokie mower and hopefully, by now you no longer have one.
Now that your mowers are fixed, you can get back to that lawn. Time to mow the lawn while daydreaming about all the fun things you could have done today instead of fixing a mower.
Bad Boy Mower Is Smoking [4 Possible Reasons]
YardSimply is supported by readers like you. We may earn an affiliate commission if you purchase through links on our site. Learn why you can trust us here.
I bet you despise hearing bad news. especially when you’re in the middle of cutting the grass and suddenly notice your lawn mower blowing of white smoke; it’s understandable if you have a lot of questions, the most important being: is this a serious issue? Will this problem be an easy fix?
You need to relax and take a few deep breaths because we have a straightforward answer for you. It doesn’t make a difference whether you have a 2-stroke mower or a 4-stroke mower; you shouldn’t run the mower and start looking into the common reasons for this issue.
Common Causes Your Bad Boy Mower is Smoking
Bad boy mowers contain an internal combustion engine, which can have many problems, one of them being smoke emitting from the engine or muffler. There are several reasons this may happen:
- Air Filter is Plugged
- Insufficient Engine Oil Level
- Bad Gasket in Engine
- Internal Engine Damage
Insufficient Engine Oil Level in Your Bad Boy Lawn Mower
Not only is it crucial to ensure that your Bad Boy lawn mower has enough engine oil, but it’s also crucial to avoid overfilling it. Your engine may suffer severe impacts and start to smoke if either of these oil levels is too low. Clean the foam air filter element of a Bad Boy.
Your Bad Boy Mower’s Engine Oil Level Is Too Low
Running the mower with insufficient engine oil is one of the most frequent issues that might happen. Although it appears to be a little problem, your laptop could suffer significant damage.
The engine’s moving parts start to produce friction when insufficient oil is present. As a result of this heat buildup, the oil itself may eventually begin to burn. Additionally, the engine parts may start to melt, resulting in white or blue smoke from the exhaust. In some circumstances, the damage can be irreparable, necessitating a complete engine replacement.
It’s crucial to give your mower a thorough checkup, including checking the engine oil level, before each mow: Checking the oil level in your lawnmower takes a few minutes, but it could prevent you from having to make costly repairs later. Before each usage, make sure to check the oil and add extra if necessary.
It’s also crucial to pay attention to the oil’s color; if it begins to appear black or abrasive, it’s time for a replacement.
It’s best to identify this issue quickly and avoid operating your mower under these circumstances: As with most things, it’s considerably simpler (and less expensive) to remedy an issue as it first arises than it is once it has already caused significant harm.
If you have any reason to believe your mower might not have the recommended amount of oil, proceed with caution and wait to use it until you’ve checked (and potentially replaced) the oil.
You should send your lawnmower to a qualified small engine mechanic for analysis and repair if the level lowers quickly once more because there might be a leak somewhere in the system.
The Engine Oil Level in Your Bad Boy Mower Is Too High
Generally speaking, you should always check the oil level in your lawnmower’s engine before using it. However, a lot of individuals are unaware that using too much oil might lead to issues.
Too much oil in the crankcase increases the pressure, which can then push oil into the cylinder and even into the air intake through the valve train. Your lawnmower may sustain severe harm as a result, necessitating pricey repairs.
If you discover that your crankcase has too much oil, adjusting the quantity as quickly as possible is critical.
You can accomplish this by draining a little amount of oil through the oil filter or drain plug. A tiny amount of oil from the fill area can also be sucked out using an oil evacuator or turkey baster.
After removing some of the extra oil, check the level again with the dipstick and drain the oil as necessary until it is at the proper level.
It’s crucial to check your air filter to make sure it isn’t clogged with smoke or covered in grease. If so, swap it out for a fresh air filter to stop your lawnmower’s engine from suffering any more harm.
Bad Gasket in Your Bad Boy Mower Engine
If your mower’s gasket is damaged and engine oil leaks, it may be the cause of the smoke coming from your Bad Boy. A heated surface, such as your muffler, will burn off any excess oil that has spilt onto it and emit a lot of smoke.
Internal Engine Damage on Your Bad Boy Lawn Mower
Without disassembling the engine and carrying out leak down and compression checks, it might be challenging to pinpoint the precise cause of an internal engine issue.
However, there is a straightforward test you may perform to see if your internal engine is malfunctioning.
Remove your spark plug(s) and look for any evidence of oil to finish this inspection. Oil on the spark plug may indicate a piston ring or valve train issue. Even though this check is unable to diagnose your specific issue, it will let you know that a mechanic is required to fix it.
Taking your lawnmower to a small engine repair is crucial to assess the issue and determine the cause if you carry out this inspection and discover oil on your spark plugs. Ignoring an internal engine issue could cause major harm or possibly the engine’s demise.
Your Bad Boy Mower’s Piston Rings Have an Engine Problem
Your engine must be disassembled in order to detect a piston ring issue. Damaged piston rings or scoring is found inside the cylinder wall, oil could enter and burn off, which could cause your Bad Boy lawnmower to start smoking.
Your Bad Boy Mower’s Valve Train Has An Engine Problem
An overheated Bad Boy lawn mower can have a burned valve. Only the cylinder head may be removed and tested for leakdown, which is the only technique to detect burn valve problems.
This examination and repair should be done by a small engine mechanic. The technician must precisely cut the seat and the valve to finish the combustion chamber.
You Bad Boy Mower is Blowing Black, White or Blue Smoke: What’s the Difference?
I always advise using the aforementioned techniques to locate the source of smoke coming from your lawnmower. By examining the hue of the smoke, you might be able to determine most likely its source.
Blue or white smoke is frequently produced when burning excessive amounts of oil. Oil leakage from a harmed piston ring, the valve train, the combustion chamber, or an engine gasket might cause this.
A clogged air filter may potentially be the reason oil is being driven into the cylinder.
When changing the oil, don’t forget to look for oil burning off the muffler or engine as a result of an oil leak or spill.
Black Smoke: Black smoke is produced when fuel is burned too thoroughly. This happens as a result of a clogged air filter, which permits a higher fuel concentration in the fuel-to-air ratio.
The Bad Boy lawnmower can produce dark smoke when operating heavily. Check your mower for another air limitation if the filter is not the problem.
Mowing your lawn should be a relaxing and satisfying experience, but it can quickly become a nightmare if your lawn mower is blowing white, black or blue smoke. If you’re experiencing this problem, you can do a few things to diagnose and fix the issue.
First, check the oil level and grade to make sure that they’re correct for your model of mower. Next, inspect the air filter to see if it needs to be replaced.
Finally, take a look at the angle at which you’re mowing—mowers can start smoking when tilted at angles greater than 15 degrees.
If all else fails, remember that regularly conducting an oil change is one of the best ways to prevent smoking issues (and extend its life overall).
FAQ (Frequent Asked Questions Bad Boy Mower Is Smoking)
How do I fix white smoke from exhaust?
There may be a few possible causes for white smoke coming from the exhaust of your lawn mower. According to two possible explanations, your engine is burning oil or coolant has entered the combustion chamber.
How do I fix blue smoke on my lawn mower?
If your lawn mower is smoking blue smoke, it may be because the oil is too old or dirty. Try changing the oil and see if that fixes the problem.
Can spark plugs cause blue smoke?
Spark plugs that are damaged or worn out can cause blue smoke.
Can low oil cause smoking?
Yes. If the oil level is low, it can cause the engine to run hotter than normal and this can cause increased smoking from the exhaust.
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.
This post may include affiliate links. Purchases made through these links may provide a commission for us, at no extra cost to you. As an Amazon Associate, we earn from qualifying purchases.
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.
Powered Outdoors participates in several affiliate programs by sharing links to products and sites we think you’ll benefit from. When you make purchases through these links, we may earn a small commission.