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Why Does My Lawnmower Smoke?

After using your lawnmower for quite some time, you suddenly see smoke coming out of it. All machines can break down at some point in their life cycle, and it’s handy to be aware of the problems, their causes, and how to fix them. If you are a lawnmower owner, you should know that it is always possible that your mower is blowing out smoke. If it is a lot of smoke, this can be a problem, but it can be fixed most of the time. All you need is to understand the types of smoke and why the mower blows out a specific type of smoke.

Why does my lawnmower smoke:

Lawnmower smoke can be white, blue, or black. The causes behind each type of smoke are different, and each type needs another fix. Black smoke is usually caused when the fuel is not completely combusted, and some of it turns into smoke. The reason is problems with the air filter or spark plug. Blue smoke is mostly caused by an oil overfill, an oil spill, a leaked crankcase, or because the engine is tilted at an angle during operation. White smoke is usually caused when the engine is burning oil that somehow got into the engine, and it usually ends when all the oil that went into the engine is burned. In most cases, these problems can be easily fixed.

As said above, there could be multiple reasons for your lawnmower blowing smoke, and there could be many possible fixes. Now, we’ll get into the details of these different kinds of smoke and what to do if your engine is blowing smoke.

1. Black Smoke:

● Incomplete Fuel Consumption:

A lawnmower will blow black smoke when the fuel is not being combusted completely. It is important to know that proper and complete combustion of smoke in the engine is essential for smooth working and health. In some cases, the air-fuel mixture that forms in the engine is too rich with fuel and does not have enough air to burn the fuel completely. When this happens, the fuel that is not completely combusted in the engine’s combustion chamber turns into black smoke.

– Fix:

If incomplete combustion of fuel is, in fact, the reason behind your lawnmower’s black smoke, fixing the carburetor would fix it. In an engine, it is the carburetor’s job to make the correct air-fuel mixture, and that’s why a problem with the carburetor could result in black smoke. Fixing the carburetor so that it makes the correctly proportioned air-fuel mixture is not difficult. All you need to do is to turn a screw. You should consult the carburetor section in your mower’s user manual for the right information on which screw to turn to fix the carburetor problem.

● Dirty Air Filter:

The other possible cause of black smoke could be a dirty air filter. Fixing this issue is easy. Just remove the air filter and wash it with soap and water. If it is too dirty and can’t be cleaned entirely, replace it with a new one.

● Spark Plug:

If your mower has been blowing black smoke and is not starting now, the problem must be with the spark plug. Take the spark plug out and clean its terminals off any deposits. Use sandpaper or a file to remove the deposits. If there is a buildup too big and thick to clean, replace the spark plug.

2. Blue Smoke:

An oil overfill usually causes blue smoke. If your engine is blowing blue smoke, check the oil level with the dipstick, and if the oil level is too high, adjust it so that it comes to the right level.

The dipstick is located on the reservoir. Clean the dipstick with a piece of cloth and remove the cap from the reservoir. After that, dip the dipstick for a moment, then take it out. The oil leaves a mark on the dipstick. If this mark is above the max limit mentioned on the stick or too close to it, you’ll have to drain some of the oil. For draining the oil, consulting your mower’s manual will help. So, drain the oil and check the level with the dipstick. If the level is too low compared to the manual’s recommended level, keep adding small amounts of oil and keep checking with the dipstick until it is at the right level.

3. White Smoke:

Though it is unpleasant to be surrounded by a big cloud of white smoke coming out of your mower, in most cases, it will just disappear after some minutes of the engine running. If the white smoke disappears after some time, it means that the engine burning oil was causing it.

There could be many reasons for oil being in the engine or around the engine area. You could have spilled oil on your engine’s housing or case when you serviced your mower. The heat from the engine could burn this oil to cause white smoke. Overfilling the crankcase can also result in oil in the engine and ultimately to white smoke. Oil can also spill into the combustion chamber when you turn your mower to change blades or when a riding mower moves up and down a hill or slope.

● White Smoke in Two-stroke Engines:

It is common to use a fuel-oil mixture in two-stroke engines, but the mixture’s correct proportions and fuel are significant. The normal oil to fuel ratio in the fuel mixture for two-stroke engines is usually 50:1 to 40:1. Using a little excess oil in this mixture isn’t too harmful to the engine but if you want to get rid of the smoke immediately, change the fuel with the correct mixture.

● White Smoke in New Lawnmowers:

Sometimes when you operate a new lawnmower for the first time, it produces white smoke. As bad as white smoke coming out of a mower that you have just bought sounds, there is no need to take your mower to a repair shop right away. This white smoke is probably because of oil residues left by the manufacturer. Just let your mower run for some time so that all of the oil residues get consumed. Once that happens, the white smoke will disappear.

4. Other Causes of White/Blue Smoke:

  • Tilt angle: Using or operating your engine in a tilted position can cause leaks and send oil spills to your engine resulting in your mower smoking. Engine operating at an angle greater than 15 degrees can result in white or blue smoke. Make sure your engine is operating within the prescribed limits.
  • Problems with oil: As mentioned before, oil problems such as overflowing or using the wrong grade can cause white or blue smoke. To troubleshoot this problem, change the oil, shift to the correct grade for your machine and fill the correct oil amount.
  • Problems with crankcase: Crankcase leaks can also cause white or blue smoke. If your engine is blowing smoke of these colors, check the crankcase for any leaks.
  • Obstruction in the breather tube: Breather tube is located behind the air filter. Obstructions in the breather tube can also cause white and blue smoke. Checking the breather tube and removing any obstructions could fix the problem too.

5. When Do White/Blue Smokes Become a Serious Problem?

If your engine does not stop blowing white or blue smoke after an extended operating time and after you have checked for basic issues, this could indicate worn seals. Worn seals mean that the engine’s oil has found a way to the combustion chamber and is burning non-stop. If this is the case, your engine won’t stop smoking on its own and will sputter and/or stop. If this happens, take your mower to a mechanic for repair. Sometimes a blown head gasket can result in the air filter being soaked in oil, which causes white smoke. Just like worn seals, this problem will require the attention of a mechanic. It is important to remember that the repair shop’s visit is only advised if your engine hasn’t stopped after enough time of use.

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 distress. 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.