It is extremely fun to ride ATVs, but it is never a good idea to ride an ATV that has smoke coming out of the engine. What causes an ATV to produce smoke?

ATVs produce smoke when there is an issue with the engine, mechanics, or fluids. The timing and color of the smoke can indicate what the issue is. Typically, when there is smoke, the ATV requires immediate attention and should not be driven until the smoking issue has been resolved.

Here is a run-down of the different smoke colors that can come from your ATV, why they occur, and what you can do to fix the issue.

Blue-Gray Smoke

If you see smoke that is a hazy blue or gray color coming from your ATV, it is most likely being produced by burning oil. When oil burns, it produces blue-tinted smoke. To narrow down the cause of the burning oil, you will need to determine what kind of engine you have. ATVs can have either two-stroke engines or four-stroke engines. Two-stroke engines are becoming less and less popular, but older and smaller ATV models may still have a two-stroke engine.

If your ATV has a two-stroke engine and you see blue or gray smoke coming out of the exhaust, it may be completely normal. The way the engine is designed produces a small amount of smoke while it is running. A very minimal amount of smoke is normal, but if you notice an increase in smoke production, you should check it out before continuing to use your ATV.

If you have an ATV with a four-stroke engine that is producing blue-gray smoke, this is a much bigger concern. Even a small amount is cause for concern. It takes a lot of burning oil to create smoke in a four-stroke ATV.

Oil is burning because it is not where it is supposed to be. This could be because of a leak or broken part. It could also be caused by an issue with the oil itself.

If you start noticing smoke following an oil change, you will want to double-check the amount of oil in the vehicle and the type of oil you used. Use the dipstick to make sure the oil level is between the lines. If the oil level is above the top line, the smoke is likely caused by excess oil. When there is too much oil in the chamber, it is forced to find other places to go when the pressure is too high. The escaped oil then burns and produces smoke.

For some ATV engines, the type of oil makes a huge difference. If you did not use the manufacturer-recommended oil and your ATV starts smoking after you add oil, you should do another oil change and use the recommended oil.

If you put in the correct amount of the correct oil, the smoke is likely being caused by a parts issue or an issue with the valves. If the valves are not keeping the oil where it is supposed to be, it can leak into the cylinder and burn. Oil will leak out around the valves if the seals are damaged or poorly fitted. Valve seals can wear out over time. The leak also might also be caused by a poor fit between the valve stem and the valve guide. If there is too much space between the two, oil can leak through the gap and drip.

A valve issue can be hard to catch because only a very small amount of oil is let through every time the valve opens and closes. If the damage is minor, you may not notice it while you are riding. A valve issue will be most obvious when you first start the engine.

You will also want to investigate the connections to the combustion chamber, as oil can often leak into this chamber and burn. Cylinder walls and piston rings wear down over time and might allow oil to escape. In this case, the oil will drip more consistently and in larger quantities than if there is a valve issue.

White Smoke

White smoke with no tinge of color is usually steam. It is normal to see a little bit of white smoke or steam when you first start an ATV. When the ATV sits for more than a couple of hours, water vapor can build up, especially if you live in a humid area. This normal start-up white smoke clears very quickly and should never last longer than a minute.

If the white smoke lasts longer than a minute, there is a more serious problem. When the smoke is white like steam, it means that whatever is burning is water-based. In this case, it is likely coolant. When coolant burns, it produces a slightly sweet smell. This will help you tell whether what you are seeing is vapor or smoke.

Coolant can get into the combustion chamber when there are damaged or broken parts in the ATV’s engine. The combustion chamber is very hot, causing the coolant to evaporate and produce smoke.

If there is a crack in the cylinder, coolant can leak out. The crack could be on the head or on the deck of the cylinder. Cracks along the cylinder or cracks in the engine block occur as the parts get old.

Coolant also often leaks because of the gasket. A damaged or blown gasket is one of the most common culprits of burning coolant and white smoke. Whether the gasket is just damaged or completely blown, you should replace it with a new one if your ATV is producing white smoke because of it.

Black Smoke

Dark black smoke means that fuel is burning somewhere in the ATV’s engine. You will likely be able to guess that fuel is causing the smoke because of the distinct smell. Be very cautious when you see black smoke because fuel can ignite quickly.

When you see black smoke, it is almost always because the air-to-fuel ratio inside the engine is off. This means that a broken part or leak is causing the fuel ratio to be way too high. There are a few possible causes of an increased fuel ratio.

Ideally, the black smoke you are seeing is an easily resolved issue. When you first see black smoke, check your air filter to see if it is dirty or clogged. When the air filter is too dirty, it does not allow enough air to pass through into the vehicle. The carburetor requires a certain amount of air to properly control and mix the air and fuel. If the amount of air is too small, there will be excess fuel that cannot be used properly and will become smoke.

With a lack of air, the engine may begin to lose power. This is one of the quickest problems to fix, as you can fix it at home. All you need to do is clean the air filter. While you have it out of the ATV, check for tears or holes. If the air filter is damaged, it needs to be replaced.

If cleaning the air filter doesn’t fix the issue, check the fuel injector. It will drip extra fuel when it is cracked, damaged, or clogged. Clogs in the injector make the fuel flow unevenly, creating issues with the air-to-fuel ratio.

If the fuel pressure regulator is not working properly, it will not be able to regulate how much fuel goes into the engine. The electronic fuel injector may be programmed incorrectly and allow too much fuel to go into the engine. Also, if the fuel return line is clogged or broken, not enough fuel will be removed from the engine to maintain a good fuel-to-air ratio.

How you can stop your ATV from producing black smoke might depend on what kind of engine you have. A two-stroke engine can have issues with broken or cracked reeds within the engine system. If your ATV has a four-stroke engine, you don’t have to worry about broken reeds. However, four-stroke engines can have issues with the intake valve not properly regulating fuel. If your ATV has a broken or damaged intake valve, it will produce black smoke. This can also occur if the intake valve isn’t properly fitted to the rest of the system.

Smoke Only When the Engine Starts

If your ATV only smokes when you start the engine, it might not be caused by a big issue. If white, cloudy smoke comes out of your ATV’s engine when you start it but dissipates after 20-30 seconds, nothing is wrong with the engine. This is especially the case if the smoke doesn’t have a strong or harsh smell.

When an ATV sits unused for a while, it will likely accumulate some moisture from water in the air. This may be especially prevalent if you store your ATV outside, you live in a humid area, or it rained recently. As the engine and motor heat up, the water evaporates. This will happen very quickly and may not even be very noticeable in many cases.

If you see smoke when you start the ATV that goes away quickly but does not match that description, it may be caused by oil. Oil will produce bluish or grayish smoke when it burns and will be more like the smoke from a fire rather than just a cloud of vaporized water. It will have a strong, bitter smell as well.

If your ATV only produces blue smoke when you first start it, it always indicates that there is an issue with the engine valves. This issue is seen in ATVs with four-stroke engines because they have valve stems, springs, rockers, and guides above the rest of the engine. These valves slide in and out of their guides in sequence.

It is important for the valve stem to fit very tightly inside of the valve guide to prevent oil from leaking through in between them. Typically, a rubber valve seal is placed on top of the guide, allowing the stem to move through, but nothing else. These rubber seals can easily stretch, crack, or become displaced over time.

Small amounts of oil are let through every time the valves move, which is done constantly while the engine is running. However, the amount is so small that you may not notice it. Valve leaks are mostly noticeable only when you first start the engine. While the vehicle is not running, oil is still slowly leaking through.

Since the engine is cool, the oil does not burn but pools up. When you go to start it the next time, the pool of oil will burn once the engine gets hot and will produce a cloud of blue smoke. The smoke then dissipates and becomes unnoticeable again. If your ATV only produces smoke for a few minutes after you turn it on, it is likely that only a small amount of oil has leaked onto the engine.

Smoke when the Engine is Revved

If you see smoke coming from your ATV each time you rev your engine throughout your ride, a little bit of oil is leaking each time you rev your ATV’s engine. Based on the parts that move when an ATV’s engine is being revved, the smoke is most likely being caused by the piston rings. The rings may be damaged, broken, missing, or poorly fit. These rings are important for maintaining the seal on the piston. If the piston is not sealed properly, it will leak oil every time it is engaged.

This smoke will smell and look like other oil-based types of smoke. It will likely be greyish in color and smell bad. You will see small-ish plumes of smoke coming from the ATV anytime you make the engine rev. The smoke should stop being produced as soon as you take your foot off the gas pedal.

Luckily, piston rings are fairly cheap and easy to replace. You can get a few piston rings for $9-$10. You can also get rings, pins, and a piston set for $20-$25.

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