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Lawnmower smokes when running, this is how you fix it

A moment of concern occurs using your lawnmower when the machine starts to blow smoke. When you give your Lawnmowers regular maintenance, this should not happen often, but like all mechanical machines, there is always a chance that something does not work as it should. There can be many reasons for the smoke problem that we will discuss in more detail. In most cases, the problem can be fixed easily. But some issues are tough to fix. But leaving the situation untreated can cause many future issues and costly repairs. 

Lawnmower smokes when running, this is how you fix it:

When your lawnmower smokes when running, this can be due to several reasons. The first step is to check the color of the smoke. Black smoke is typically caused because the fuel is not entirely burnt, and part of it transforms into smoke. Blue smoke is often caused by an excess of oil, an oil spill, a leaking crankcase, or a tilted engine at an angle during operation. White smoke is generally caused when the engine burns oil that somehow gets into the engine and usually comes to an end when all the oil that went into the engine is burnt.

After identifying the smoke color, you can look at the various reasons why your lawnmower smokes. If you can not judge the smoke color, you will need to look at the causes for more than one color. Also, understand that older lawnmowers will often smoke more than younger ones. Talking to a lot of lawnmower owners clearly shows that the lack of maintenance is an important factor in a lot of cases. Always make sure that you are regularly cleaning and maintaining your machine. And at the end of the season, you should do an even more thorough inspection. You can do this yourself or bring your machine to a good mechanic.

The Key Components Causing a Lawnmower to Smoke

Knowing all of the key components will help you understand the reason and fix your lawnmower smoke problem.

● Component 1: Carburetor

The carburetor is the part of the lawnmower that controls the proper supply of air and fuel for combustion. It takes in fresh air from intake and fuel from the storage tank. Combining fuel and air in appropriate proportion moves the mix forward to the intake valve for entering the engine to burn.

● Component 2: Head Gasket

The Head gasket’s role is to provide a seal for fluid inside the engine and outside or around it. And to keep the high pressure of combustion inside to get a maximum energy transfer as good blade rotation.

● Component 3: Air filter

Filter the incoming air before mixing it with the fuel in the carburetor. The lawnmower has to work in very dusty conditions, and an air filter plays an important role.

● Component 4: Oil filter

Filters the oil so that the lubrication process does not cause any rashes. Even if oil gets to combust engine remains safe. It has a more critical role in a 2-stroke engine.

● Component 5: Breather Tube

The tube that is clogged will hinder the working of the carburetor and hence the lawnmower.

● Component 6: Fuel filter

This component filters the fuel for any undissolved carbon or metallic particles that will cause engine damage.

● Component 7: Oil rings

Present around the piston of an engine. These seals provide an obstacle to oil film trying to get in the combustion chamber.

Moving further, we will discuss the cause of the smoke, categorize it, and provide a fix for them.

Lawnmower Black Smoke:

● Carburetor: Incomplete Fuel Consumption

It is necessary to note that proper and complete combustion of smoke in the engine is crucial for smooth operation and health. In certain situations, the air-fuel mixture that forms in the engine is too rich in fuel and does not have enough air to burn the fuel thoroughly. When this condition occurs, Blacksmoke is blown from the exhaust.

Category: Black smoke, Danger level: Average  

– Fix:

Blocked air filter:

A dirty air filter may be another possible cause of black smoke. This task is a day-to-day repair process that you can review during each session of use.

Category: Black smoke, Danger level: Average  

– Fix:

  • Step 1: Take the air filter out from under the cover
  • Step 2: Examine the health
  • Step 3: Wash the dirt off using soap and brush
  • Step 4: Let it dry
  • Step 5: If the air filter is in terrible shape, replacing it is a better idea

● Dirty Fuel Filter:

Right by the side of the carburetor between the fuel line and venturi, a fuel filter is present. A dirty fuel filter will result in smoke.

Category: Black smoke, Danger level: Relatively high  

– Fix:

  • Step 1: Block the fuel supply using clips
  • Step 2: Carefully pull out the supply
  • Step 3: Remove the strainer and wash it thoroughly
  • Step 4: Drain old gas and filter it through a sieve
  • Step 5: Refill with filtered gasoline

● Lousy Sparkplug:

If your mower has been blowing black smoke and is not starting now, the problem must be with the spark plug.

Category: Black smoke, Danger level: Average  

– Fix:

  • Step 1: Remove the wire from terminal
  • Step 2: Unscrew the plug
  • Step 3: Check for the appropriate condition
  • Step 4: Clean the carbon from head
  • Step 5: Gap the plug and insert back
  • Step 6: If the sparkplug has abnormal insulation or resistance changing it is the right thing

● Breather tube

Breather tube is generally considered to be a part of carburetor but mostly neglected. If there is a blockage in the tube, it will cause smoke from the lawnmower.

Lawnmower White Smoke:

● Blown head gasket:

Suppose the head gasket of the engine is lousy or is completely blown. Oil and coolant seep into the combustion chamber, causing white smoke.

Category: White smoke, Danger level: Relatively High  

– Fix:

  • Step 1: Open the engine compartment and examine all components
  • Step 2: Clean the surfaces
  • Step 3: Clean the carbon deposits
  • Step 4: Check the condition of the gasket
  • Step 5: If completely blown, replace it
  • Step 6: If partially damaged; use gasket-sealant paste around

● Oil rings:

Oil rings refrain the oil from between the piston and cylinder to seep into the combustion chamber. If oil rings wear out, the oil will get into the chamber and burn with fuel. This problem will cause smoke. If not treated, many problems can arise.

Category: white smoke, Danger level: Average  

– Fix:

  • Oil rings: It is customary to check for oil rings health in every engine check-up
  • Piston rings: Replacing the piston rings is the only option
  • Complicated repair: Self-repair should be avoided if the expertise level is low
  • Check the correct size: Proper size and fit should be chosen as per the instruction manual

● Crankcase leaks

Crankcase leaks can also cause white or blue smoke. If your engine is blowing smoke of these colors, check the crankcase for any leaks.

Lawnmower Blue Smoke:

● Excessive Lubricant:

Overfilling oil produces blue smoke. If your engine is blowing blue smoke, check the dipstick’s oil level, and if the oil level is too high, change it to the right level.

Category: Blue smoke, Danger level: Relatively Low  

– Fix:

  • Step 1: The dipstick is located on the reservoir. Clean the dipstick with a piece of cloth and remove the cap from the reservoir
  • Step 2: Dip the stick for a moment and take it out again
  • Step 3: Check the level corresponding to marks
  • Step 4: If the level of oil in excess, remove the oil by draining through the plug present below the oil sump

● Tilt angle: 

If the lawnmower is operated at very steep slopes, it will cause oil seepage into the engine block and cause smoke.

Category: blue smoke, Danger level: low  

– Fix:

  • Try using at less steep paths and nominal level

The Lawnmower smokes when running causes and remedies in a handy table:

To summarize all of the above mentioned causes and fixes in a handy table:

Blue smoke:
Overfilled oil
Reduce the oil by draining
Tilt angle
Operate on straighter paths
Black smoke:
Incomplete fuel combustion
Check the carburetor
Bad Sparkplug
Clean or change
Dirty Air filter
Clean or change
Clogged fuel filter
Please clean it
Breather tube
Remove dirt particles carefully
White smoke:
Blown head gasket
Replace or repair
Crankcase leak
Get the case repaired with a sealer
Bad Oil ring
Change the rings

Related Questions

1. Is it okay for the 2-stroke engine to smoke?

No, for any engine blowing smoke is not normal. Although a two-stroke engine burns oil, the proportion of oil added in fuel should be maintained. If not appropriately maintained, blue smoke will be produced and will result in damage to the engine too.

2. What if a brand-new mower blows smoke?

There is still nothing to worry about. Brand-new engines have some leftover oil from the manufacturing phase left inside the cylinder. The smoke will go away after a few usages. If the smoke clouds persist, then exchanging the mower or getting it checked is the only option.

Final Remarks

For people who have no idea of the nature of issues resulting in their mower blowing smoke, mower smoke could cause significant worry and stress. The mower blowing smoke is mostly caused by problems that are not too serious and can be fixed easily. Let your smoking mower run for some time in case of white and blue smoke. In most cases, it will stop smoking after some minutes. Otherwise, follow the instructions mentioned above. In the case of black smoke, all you have to do is ensure that your fuel is correct and the carburetor and air filter are in the right shape.