What Causes a Two Stroke Engine to Smoke? 6 Common Issues

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Two stroke engines are some of the most common mowers in the world. They’re easy to maintain and they don’t cost too much, but they tend to get a bit leaky every now and then. Leaks lead to smoke, and next thing you know, you’re pushing a smoky mower around the yard.

When a two stroke engine starts to smoke, it’s caused by burning oil, clogged air filters, damaged head gaskets, or failed piston rings. However, new mowers often have excess lubrication that needs to be burned off, hence the bit of smoke you might notice.

Throughout this article, you’ll discover the following information about what causes a two stroke engine to smoke:

  • Various causes and solutions that will stop the engine from smoking
  • How you can treat a smoking mower without getting a new one
  • Preventative methods to keep your engine free of smoke

Pro Tip: Old or incorrect engine oil can ruin a mower in a matter of minutes. In fact, the vast majority of mowers end up getting tossed before their time. Check out the best two-stroke engine oil on Amazon.com to keep your mower alive and thriving for a long time to come.

Why Does My Mower’s Two Stroke Engine Smoke?

A two-stroke engine mower can emit blue or white smoke during mowing. Here are some of the reasons why this may happen:

Oil spills on the engine

The mower might emit white or blue smoke if you’ve recently changed the oil in your mower. This could signify that oil spills have occurred on your engine.

These oil spills could have happened when mowing on a sloppy area beyond fifteen degrees or when you tip your mower over for cleaning or maintenance.

Garden Tools Expert points out that burning oil is the most common cause of white smoke on a two stroke engine.

Clogged air filters

Enough air is vital for combustion to take place in the combustion chamber of a two-stroke engine mower. Clogged or dirty air filters hinder airflow, which makes the combustion process incomplete. The unburnt fuel that is present in the combustion chamber causes white or black smoke.

Adding too much oil to gas

An engine with less oil has a lot of friction during operation due to a lack of lubrication. If excess oil is added, it will slip through into the cylinder and start burning along with the fuel. This will lead to excess smoke being emitted from the exhaust.

Excess engine oil will also come out of the exhaust muffler. The usual air-fuel ratio for a two-stroke mower is between 50 to 1 and 40 to 1. The excess oil won’t hurt the engine, but you’ll have to change the fuel to stop the smoke.

It’s a new mower

A mower may produce white smoke on its first day because there might be oil residues left by the manufacturer. To solve this, you let the lawnmower run for a while. 

The engine of the mower will burn off the residue oil, and the smoke should stop.

Is your lawn mower sputtering more than it should, though?

Damaged or leaking head gasket

As stated by Hunker, the head gasket is a seal that keeps the engine closed off. The gasket is found in an area where the cylinder joins with the rest of the engine.

A damaged or leaking head gasket emits constant white smoke that doesn’t go away even after running the engine. Many compressions are usually present in the cylinder that sucks oil from the crankcase even if there is a small leak in the head gasket.

As oil enters the cylinder, it starts burning, causing white smoke. The smoke continues to increase if the engine keeps running since more oil is sucked into the cylinder.

You may hear the sound of air being blown from the leaking gasket and loss of compression, which causes low power output from the mower.

The oil flow rushing into the cylinder may cause it to stop running after a while or even fail to start.

Failed piston rings

If your mower is burning up a lot of oil and producing white smoke as it runs with very little to no power, then it can mean that your mower has bad piston rings. This is mostly seen in older worn out lawnmowers or poorly maintained mowers.

It’s the worst cause for white smoke production as fixing the mower is very involving. Piston rings control the amount of engine oil and supply very little oil to the piston to move smoothly inside the cylinder.

They also remove excess oil from the combustion chamber and flow it back into the engine block. Damaged piston rings can occur due to the following reasons:

  1. Insufficient lubrication due to dirty engine oil or lack of timely oil change could damage the piston rings.
  2. Dust entering through worn out air filters find their way into the combustion chamber damaging the piston rings.

How Stuff Works shows us that leaking oil isn’t too uncommon in two stroke engines.

How to Fix a Smokey Two-Stroke Engine

● Restart the mower

An easier way of fixing oil spills in your engine is by restarting your mower to ensure the spilled oil is burned off. It’s advisable to check your owner’s manual to determine the best way to reduce the risk of oil leaks, especially if you tip your mower over regularly for cleaning and maintenance.

● Check for overfill and drain excess oil

An overfull oil reservoir may also cause white or blue smoke. To avoid the accidental overfilling, refer to your mower’s user manual to find out the exact amount of engine oil your lawnmower needs.

Once you have put engine oil in your mower, check the dipstick’s oil level located on the reservoir. Compare the oil level with the recommended level indicated on the stick. If you’ve put excess, then you will have to drain the oil and fill the engine again to the required level.

● Replace a damaged head gasket

A damaged or leaking head gasket can only be replaced since it’s not repairable. Head gaskets are not expensive, and you can get a quality one at an affordable price.

Repairing damaged or worn piston rings are not easy as it requires a complete engine rebuild, and the whole engine will need to be opened up.

If your lawnmower has bad piston rings, then chances are the head cylinder will also have signs of damage and will need to be replaced as well.

The repairing process involves a lot of expertise, and it’s best to leave it to a professional. However, it’s advisable to purchase a new engine as a repaired one tends to not work like a new one.

How Do You Prevent It from Happening?

Maintenance is key to avoiding smoking while using your mower. The following tips should help you avoid smoking incidences;

  1. Ensure that you regularly replace dirty/old oil with new, clean oil.
  2. Ensure that you check the air filters for dirt and clean if any is found to avoid clogging that will prevent enough air from getting into the combustion chamber.
  3. Before overfilling your engine, always ensure you use the dipstick to check the amount of engine oil required.

To learn more about why lawn mowers emit white smoke, click here.

Final Thoughts

Are you tired of pushing around a smokey lawn mower? Whether it’s from leaky oil or a broken head gasket, it’s important that you get to the source of the problem as quickly as possible.

Here’s a quick rundown of everything this post should’ve taught you:

  • Smoke isn’t always a sign that your mower needs to be fixed or replaced.
  • Some parts are irreparable, which means you’ll need replacements or a new mower.
  • If you notice your mower is smoking, turn it off immediately, wait half an hour, and diagnose the problem before you use it again.
  • Most smoking two-stroke engine problems are due to burning oil or a leaky gasket.

Jonah

Jonah loves researching new ways to grow and maintain healthy plants. If he's not writing on one of his many blogs, he's likely playing acoustic guitar, watching survival shows, or mapping routes for future road trips.

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