7 Reasons Your Lawn Mower is Smoking (and How to Fix It)

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Seeing smoke come out of your lawn mower is enough to alarm anyone. Smoke means there is a problem, but in most instances you don’t have to take it to an expert. As I will show you, the solution – whether it is white, black or blue smoke -is something you can often do without professional help.

If a lawn mower emits blue or white smoke, there is probably too much oil in the tank and has spilled over. Black smoke means the fuel mixture is too rich or the air filter is clogged.

The smoke color gives you an idea of the cause and how to resolve it. Smoke often affects gas lawn mowers, but it can also happen to electric models. Keep in mind the location for specific parts may vary from one model to the next. Check your owner’s manual if you are not sure.

Before starting, take all precaution necessary. Wear protective gear and be careful when handling fuel or electrical wires.

Fuel Spill on the Engine

Blue or white smoke usually means oil has spilled out on the engine. There are three scenarios where this can happen.

  • The first is if you changed the oil. You might have put too much and the fuel spilled over.
  • You flipped the mower on its side to fix something. This caused the oil to spill over. This can happen if you put too much in the tank.
  • You are mowing at a 15 degree or higher slope. At that angle and with a full tank, fuel could seep out.

Solution. All you need to do is turn the lawn mower on and let it run. This is going to burn the excess fuel until it is gone. This might take a few minutes or more depending on how much excess oil there is.

Eventually the smoke is going to evaporate. You can continue mowing or turn it off and clean the engine first. I use Desin Engine Cleaner because it is effective for lawn mowers and other garden tools.

Too Much Fuel in the Tank

This is pretty self-explanatory. Too much fuel in the tank and it will spill over. When the engine starts, there is going to be a lot of blue or white smoke. Overfilling usually happens after a refill, but it is easy to fix.

Solution. Open the tank and pull out the dipstick. Clean it and put it back in. Take the dipstick out and compare its level with that of the stick.

If it is higher than the stick, drain the fuel tank. Pour fresh fuel until it is about 70% of the recommended volume. Now put the dipstick in and pour small amounts of fuel until it reaches the stick fill line.

Wrong Fuel

Lawn mowers require specific types of oil to run. Check your owner’s manual for information about this. If you use the wrong oil, the engine will stall and emit blue or white smoke.

Solution. Many four-stroke lawn mowers use 10W30 oil like Pennzoil. Yes, lawn mowers use regular gas, but they also need motor oil to run.

In most cases 10W30 will work but you should look into the manual to be sure. But in my experience, if the motor oil works for cars, it will work on lawn mowers too.

Fuel Mixture is Too Rich

Lawn mowers need the right air to gas ratio to work. If there is too much gas and not enough air, the mixture is “rich”. This usually produces black smoke and a strong gassy odor. This can also be one of the reasons why your lawn mower won’t run after winter.

Solution. The carburetor is responsible for the gas and air mix. Before you tinker with the carburetor, I recommend cleaning or replacing the air filter first.

If the filter is dirty, air won’t be able to get in the carburetor. Clean or replace the air filter and turn the engine on again. Let it run for a few minutes.

If it continues to emit black smoke, you have to adjust the carburetor. This video shows you how it is done.

Carburetors have adjustment screws. You have to turn these in increments and observe the effect on the engine. Keep adjusting until the engine no longer has black smoke. That means the gas and air mixture is now correct.

Defective Lawn Mower Belt

The belt makes it possible for the blade to work. If the belt is defective, worn out or damaged, the blade cannot spin. This causes the motor to overheat as it tries to make the blade run. After a while the motor will start to smoke.

Aside from smoke, there are other signs of a broken mower belt. These include loud noises when you run the mower and the blade will not spin.

Solution. The only option is to replace the belt. Any physical damage to it requires replacement. Check your manual for the right belt size and type. You can buy a replacement online or in a brick and mortar shop. If you decide to buy in person, take the broken belt so you can point out exactly what you need.

Overheating Electric Motor

Electric lawn mowers like those today have powerful motors. But even these can overheat and produce smoke.

The most common causes of an overheating motor are:

Very thick and tall grass. If the grass is too thigh and/or thick, the motor could smoke and overheat. The lawn mower might not have enough power to mow overgrown grass.

Clogged motor. As you mow, grass clippings and dirt accumulate under the deck. This can clog the mower and prevent it from cooling down. So even when you turn off the motor, it remains hot Eventually it starts to smoke.

Jammed blade. The blade might be jammed. Turn the mower off and check if there is something stuck on the blade.

Worn out motor. If you have an old electric lawn mower, it probably doesn’t have enough power left. The older the components, the more vulnerable they are to overheating.

Solution. It depends which problem your lawn mower has. A clogged motor or jammed blade requires cleaning. For protecting thea blade I prefer Stab-bil Blade Guard because it is cost effective and efficient.

If the motor or other parts are worn out, take it to a repair shop. However if the motor does not have enough power to mow your lawn, you have to buy a new lawn mower.

Wiring Problems

Frayed wires lead to shorting, which is dangerous. Not only does it smoke and cause heat, but this can start a fire.

Wires get damaged for various reasons, such as improper storage. If you leave a lawn mower outdoors, it will be exposed to the elements.

Solution. If you suspect this is the case, follow these steps. Warning: be careful when handling electrical wires.

  1. Turn off the lawn mower. Disconnect from the power source.
  2. Take a look at the wires. Remove all frayed or damaged wiring. Do not repair them, get a replacement.
  3. If there are no more frayed wires or damage anywhere else, install the new wires.
  4. Plug into a power source and turn the lawn mower on.

Do this only if you have knowledge handling electrical wiring. Otherwise I suggest let a professional do it for you.

When to Take a Lawn Mower for Repairs

The suggestions above usually fix lawn mower smoke problems. If you tried them all and nothing worked, it’s time you take the lawn mower to a repair shop. Your lawn mower has some major issues.

Most likely there is a busted seal or crankshaft. Or other engine components might need to be replaced. If you have an electric lawn mower, some electronic or motorized parts may be damaged.

If you see smoke come out of your lawn mower, try the solutions here first. You should only take it for repairs if none of the techniques here worked.