Lawn Mower Blowing Black Smoke- Causes & Solutions

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The color of lawn mower exhaust may vary. Each kind of smoke has its distinct reasons, with a particular remedy. Unburned fuel particles often produce black smoke.

A filthy air filter or a broken spark plug are two possible culprits. An oil spill usually causes blue smoke, an oil overflow, a leaky crankcase, or an engine tilted while operating. White smoke signifies that oil has entered the engine and is being burned.

When the exhaust from a lawnmower appears black, it is typically due to an overly high fuel-to-air combination. During operation, the lawnmower is most likely using more gasoline than is required.

Suppose you see black smoke emerging from your mower. In that case, oil has entered the cylinder and is burnt alongside the gasoline. Under some conditions, the lawn mower may refuse to start.

Is it Risky to Breathe in Lawnmower’s Black Smoke?

Is it Risky to Breathe in Lawnmower's Black Smoke?
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The lawnmower’s black smoke isn’t just unsightly; there are health risks associated with breathing it in. To begin, the soot from the unburned gas or fuel makes the smoke black as it is expelled via the exhaust.

Inhaling gasoline fumes is unhealthy; you certainly don’t want to breathe in all the sooty gasoline through your engine. Furthermore, if your lawnmower is emitting black smoke, there may be an issue on the inside.

Choke components, air filters, spark plugs, and even the carburetor may need to be replaced if your lawnmower is burning too high of a fuel/air ratio. The appearance of black smoke indicates the need for immediate action.

Black Smoke from Lawn Mower: Causes

Black Smoke from Lawn Mower: Causes
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The same high fuel and air combination that drives the same problem with push mowers causes black smoke from riding lawnmowers. First, ensure the choke and air filter are clean and working correctly. If so, maybe the carburetor is broken.

4 Stroke Lawn Mower

Both 4-stroke and 2-stroke lawnmowers produce black smoke for the same reasons, in contrast to their electric counterparts, which make white or blue smoke.

The only real distinction between push mowers is the choke type. If your lawnmower has a priming bulb, then the choke is not the problem, and you should check the air filter or carburetor instead.

2 Stroke Lawn Mower

As I indicated above, the same thing that causes black smoke to come out of a 4-stroke mower also applies to a 2-stroke mower.

All lawnmowers have a common source for their black smoke emission: the fuel-to-air ratio. To be clear, though, this is not always the case with white or blue smoke.

Also Read:- Why is My Lawn Mower Blowing White Smoke?- How To Fix

Why the Smoke From My Lawnmower is Black?

Why the smoke from my lawnmower is black
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Suppose the engine of your lawn mower is emitting black smoke. In that case, one or more of the following may be to blame:

  • The choke is set to or stuck in the “on” position.
  • The air filter is clogged.
  • The carburetor is malfunctioning.

When there is excessive fuel in the mixture, the engine is rich, and if there is an inadequate amount of gasoline, the machine is lean.

Let’s investigate all the potential causes of the black smoke coming from your lawnmower’s engine.

Also Read:- How to Stop a Lawn Mower From Smoking?

1. Adjusted or Fixed “On” Choke

A choke or priming bulb may be used to start a lawnmower whenever the engine is cold. When you initially start up your lawnmower, the choke allows you to increase the amount of fuel-to-air ratio.

The term “choking” refers to limiting the quantity of air entering the carburetor to increase the concentration of gasoline in the mixture.

A priming bulb pushes more gasoline into the engine, improving combustion. You may remove the choke when the engine is up and going and has warmed up a little. If the burner is left on or stuck, the black smoke comes from the rich mixture of fuel and air.

Black smoke is produced only by manual and automated chokes; priming lamps have no effect.

First, make sure the choke isn’t set too low. If the choke seems to be operating correctly, you may need to inspect the air filter or the carburetor. If that is not the case, try adjusting the choke settings and seeing if it improves the lawn mower’s performance.

2. Air Filter Clogged

The air filter on your mower is essential, and it should be inspected and cleaned at least twice every growing season. A new air filter should be installed every 100 operating hours and cleaned every 25. 

A clogged or soaked air filter might prevent enough air from reaching the engine, leading to engine failure. It is another route to the rich fuel-air combination that results in soot. Most lawnmowers, fortunately, include an air filter that is simple to access.

If you suspect that dust and debris on the air filter are to blame, you may clear it out to see if it helps. You should generally throw it away if it has become damp or greasy.

If the black smoke persists after you have cleaned or replaced the air filter, try restarting the mower. It is a quick and straightforward method for introducing unwanted debris into your engine or carburetor.

However, I would not propose removing the filter and using the mower without one to see whether the filter is the source of the issue, as others have suggested.

3. Challenges With the Carburetor

Suppose you’ve confirmed that the choke & air filter is functioning normally. In that case, the problem is likely with the carburetor, even though this is seldom the case.

The carburetor’s function is to blend gasoline and air before releasing them into the engine. Failure to properly mix gas and air might cause engine malfunction. A shortage of airflow from the carburetor causes black smoke.

Also Read:- How to Clean a Lawn Mower Carburetor?

How to Clear Black Smoke from Lawn Mower?

How to Clear Black Smoke from Lawn Mower

To fix a lawnmower emitting black smoke, you must correct the imbalance between the air and gasoline burned by the engine. So, let’s look at the three potential reasons for a rich fuel mixture and the respective solutions.

Adjusted or Fixed “On” Choke

In the case of a lawnmower with a lever-operated choke, disengaging the choke while the machine is in operation may solve the problem. However, more investigation is required if that fails or if an automatic choke is present.

Manual

When the lawnmower is running, try adjusting the choke to see if that improves engine performance. To keep the engine running smoothly, you should release the choke and vice versa.

You may need to tweak the wires that open and close the choke flap if it doesn’t function properly. Carburetor removal is often necessary for this task, despite its relative simplicity.

Automatic

A lawnmower’s automatic choke may be a feature of more recent models. They can automatically adjust to the current temperature. The temperature gauge should release the throttle when the engine heats up (turning it off). 

In comparison to adjusting a manual choke, replacing these components might be a bit of a challenge. A broken thermometer or loose links on the choke flaps are likely to blame if it’s not functioning as intended.

Air Filter Clogged

A dirty filter is simple to clean. It is possible to remove dust or debris from an air filter by blowing it off with compressed air or tapping it against a clean surface. Typically, the filter is secured with little more than a plastic clip, wing nuts, or tiny bolts.

Keeping your mower’s air filter clean is beneficial in more respects than one. You’ll need to change the filter if it’s been exposed to water or oil. Inexpensive as a replacement item, putting in a new filter is as easy as taking it out.

Challenges with the Carburetor

The carburetor is the most likely culprit if the air cleaner is clean and the choke is off. When a carburetor lets in too much air, you may adjust the airscrews or get a new one.

Carburetor airscrews are consistently tightened to the same exacting degree to regulate airflow. The proper screw setting can only be determined by consulting the owner’s handbook or technical specifications provided by the manufacturer. As a rule, you must rotate the screw and back it out several times.

Carburetor replacement is required if the removal of the unit reveals that the adjusting screw was already in the correct position. It shouldn’t be too expensive to do yourself, depending on the sort of lawn mower you have.

You should take your carburetor to a minor engine repair if you don’t feel comfortable dismantling it yourself or don’t know how to do so.

Recommendation

It should go without saying, but just in case: smoke usually indicates fire.

Carefully assessing your problems is essential, as is taking all necessary safeguards.

You can get off to a good start with the information in our gas generator safety guide. If you’d instead not read it, at least be prepared with a fire extinguisher (at a minimum).

Also, if things appear to be getting out of hand, don’t hesitate to contact the fire department. Pride should never get in the way of getting aid when needed, mainly if the danger results in injury or property loss.

FAQ’s

Why does my lawnmower belch up black smoke?

If your mower is producing black smoke, it may be “running rich” or using too much fuel. The carburetor in your lawn mower controls the fuel-to-air mixture. A more significant amount of gasoline in the mix might result in black exhaust smoke if the carburetor isn’t receiving enough air.

What is causing my lawn mower to emit smoke?

Overfilling the crankcase with oil is the most common source of blue or white smoke from the engine. The other cause can be the lousy oil quality and using a machine at an angle of more than 15 degrees.

When using a lawn mower, what happens if too much oil is used?

Injecting excessive oil into the lawnmower’s engine might hinder its performance and cause damage. Overheating the machine using too much oil may lead to ruined seals, burst gaskets, or hydro locking.

Why is my lawn mower burning after I refilled it with oil?

When oil is spilt on a hot engine or muffler, when there is not enough oil in your crankcase, or when the improper engine oil grade is used, your lawnmower will begin to smoke after the oil has been changed. Changing your oil shouldn’t cause significant smoking issues, so you can be back to mowing the grass in no time.

When does a head gasket blow, and how can I tell if that’s the case with my lawnmower?

If the mower is losing power or refusing to start, and you also detect an oil leak, the gasket is likely to blame. Even if there is no oil leak and the mower still turns off at curves, the problem might be a faulty gasket because the combustion pressure is too low to keep the engine running.

Conclusion

Mower smoke may be alarming to onlookers who aren’t aware of the potential causes of their mower’s smoke emission. Mower smoke usually indicates a minor problem that can be fixed with little effort. Let it run for a time if you see white or blue smoke from the burning mower. After a few minutes, people usually stop smoking. If your vehicle is emitting black smoke, check the gasoline, carburetor, and air filter to see if any of these might be at fault. Unless otherwise specified, please follow the preceding instructions.

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