Why Your Troy-Bilt Lawn Mower Is Smoking (White, Black, Blue Smoke)

Mowing your lawn when suddenly you notice smoke coming from your lawn mower can be alarming. All you can envision is the money going up in smoke when you think about the repairs you are going to need.

A Troy-Bilt lawn mower can begin smoking as a result of a plugged air filter, insufficient engine oil level, or a bad gasket. It may also smoke because of internal engine damage like a valve train or piston ring problem.

I’ll go through the simple things to check on your mower and let you know when it’s time to get a small engine mechanic involved.

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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.

Why Your Troy-Bilt Mower is Smoking White, Black or Blue Smoke

Clogged Air Filter

An air filter is a simple part that keeps dirt and debris from entering the air intake and your engine. Even though your mower will run without an air filter, you should never operate your Troy-Bilt mower without a filter.

When you do so, your engine will be compromised and its life span will be shortened. The amount you’ll save by not using air filters will be significantly less than the cost to repair or replace a damaged engine.

Now that you know you should always use an air filter, it’s important to keep it clean. When your air filter becomes plugged, your engine is starved of air.

The engine can begin running rich because of the lack of air being mixed with fuel. This can cause black smoke to emit from your Troy-Bilt mower because more fuel is being burned than air.

Another result of a plugged air filter is when your mower pulls air out of the crankcase because it is the only air supply it can find. When air is pulled out of the crankcase, oil is also pulled into the cylinder. It emits smoke when the oil burns off.

Check your air filter at least a couple of times each mowing season. You should check it more often if you are operating your mower in dry and dusty conditions.

Here are steps to clean your paper air filter:

• Remove your Troy-Bilt air filter by removing your filter cover from the air filter housing and gently pulling out the filter. Be careful so you don’t knock dirt into the air intake.
  
• Wipe any dirt that remains in the housing with a clean dry rag.
  
• Tap your air filter against a solid surface to knock as much loose dirt out of your air filter as possible. Never use an air compressor to blow out your paper filter.
  
• Hold your filter up to the light. You can reuse your air filter if you can see light shine through the paper element. You need to replace your filter with a new one if you can’t see light.

Some Troy-Bilt mowers will use a foam filter. Follow the instructions in this article to clean your foam filter or pre-cleaner.

Insufficient Engine Oil Level

Most engines in a Troy-Bilt mower use a dipstick to help you gauge the correct level of oil in your mower. You need to make sure your engine’s oil level registers on your dipstick to the full level.

Do not put too much or too little oil in your lawn mower as it can result in engine problems and smoking.

Low Engine Oil Level

Oil is required in your engine to lubricate your engine’s moving parts. When there isn’t enough oil in the crankcase, the lack of lubrication can cause increased friction.

Your engine will run very hot which can melt your engine parts. In addition to your parts melting, your oil will begin to burn off creating smoke.

Oftentimes, once your mower becomes this hot, extensive damage is done. Your engine will need to be repaired by a small engine mechanic or replaced.

You can try to add fresh oil to your engine to see if it will run, but most likely, you are well past the point to have this simple solution work.

High Engine Oil Level

Too much oil in your Troy-Bilt mower can cause increased crankcase pressure. This increased pressure will cause oil to get into your cylinder and even up to the air intake through the valve train.

The oil in the cylinder will begin to burn off creating smoke in your Troy-Bilt mower. Learn more about the effects of running your mower with too much engine oil in this article.

To correct the amount of engine oil in your crankcase and bring it to the right levels you need to drain a little engine oil. There are several different ways you can drain some oil from your Troy-Bilt mower:

• Loosen the drain plug and then quickly tighten it to only allow a little oil to drain

• Remove the oil filter and take some excess oil from the filter.
  
• Use a turkey baster (like the one from your kitchen) to suction out some oil from the oil fill area. Don’t reuse the baster for cooking purposes.
  
• Use an oil evacuator to vacuum out a little oil

Piston Ring Problem

If the prior causes are not the reason your Troy-Bilt mower is smoking, you need to identify if you have an internal engine problem.

There is an easy troubleshooting procedure you can do to help you determine you have an internal problem, but it will not let you know exactly what the internal problem is. For that, you’ll need to have a small engine mechanic perform further diagnostics.

For this easy check that can be performed to find internal damage, you’ll want to inspect your spark plug. Use either a 3/4” or 5/8” socket, depending on the mower you own, to remove the spark plug.

You’re looking for oil on the spark plug which indicates an internal engine failure.

Oil on the spark plug may indicate you have a piston ring or valve train problem. To identify either problem, you will need to have your engine torn down and checked.

There may be scoring inside the cylinder wall causing oil to enter the combustion chamber and burn off.

Valve Train Problem

Another internal problem that you could have is in the valve train where you can have a burnt valve. This is where the valve gets burned by being overheated.

A muffler that is red hot can also indicate you have a burnt valve or timing problem. The only way to verify your valve train problem is by removing the cylinder head and performing a leak-down test.

This test should be performed by a small engine mechanic at your local repair shop. If a burnt valve is found, the mechanic will have to cut the valve and seat at certain angles so it seats correctly and makes good contact with the engine block.

The valve seat needs to be installed correctly so it can complete the engine combustion chamber.  

Bad Engine Gasket

When your Troy-Bilt’s engine has a bad gasket, oil can leak onto your hot muffler causing your mower to smoke when the oil gets hot enough to burn off.

Sometimes the gasket isn’t that hard to find and replace, but it can become increasingly more difficult depending on the location of the gasket.

Difference Between Black, Blue and White Smoke

I recommend going through the list above to identify your smoking problem. However, the color of the smoke can give you a clue as to what area on your mower you need to focus on.

Black Smoke

This color usually is due to your Troy-Bilt’s engine running very rich. This is when there is more fuel being burned than air so the first thing to check is the air filter and clean or replace it. If this isn’t the issue check for another air flow restriction.

Blue or White Smoke

This color of smoke is due to the burning of 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.

You invested a considerable amount of money in your Troy-Bilt lawn mower. Checking your engine oil level and air filter before each mowing could prevent costly repairs.