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11 Reasons Why Your Dirt Bike Is Smoking & How To Fix It

Is your dirt bike smoking out the exhaust and you’re wondering if it’s normal or safe? Whether you have a 4 stroke or a 2 stroke that seems to be excessively smoking, you’re in the right place!

Whether it’s smoking black, white or blue, this article will cover all the top reasons why your 2 stroke or 4 stroke is smoking, whether it’s okay or not, what the causes might be, and how to fix the smoking that’s not supposed to happen.

What Does It Mean When A Dirt Bike Is Smoking?

Smoke can come from various areas on your dirt bike. Some or perfectly normal, and others are a cause for concern.

Smoke usually comes out the exhaust of a dirt bike, but it can come off of or out of the radiator.
Let’s look at the most common causes of why it’s smoking.

XR600 dirt bike smoking excessively out the exhaust
4 stroke dirt bikes aren’t supposed to smoke this much…

Should A 4 Stroke Dirt Bike Smoke?

Naturally, a 4 stroke dirt bike should not be smoking because there is no oil added to the gas. However, there are times when you may see a brief amount of smoke that is okay, which I’ll cover in just a moment.

What Does White Smoke Mean From A Dirt Bike?

White smoke coming out your dirt bike exhaust can be from a few different things. As previously mentioned, 2 strokes naturally produce at least some amount of smoke. 

2 stroke dirt bikes smoke because of the oil that’s mixed in with the gas. This oil lubricates the cylinder, but it comes out as smoke when it’s not fully burned from the engine combustion.

2-stroke dirt bike pre-mix
2 stroke pre-mix causes smoking out the exhaust – especially on cold start-ups

Bad crank seal

2 stroke dirt bikes have crankshaft seals that separate the crankcase from the transmission. If a crank seal goes bad, transmission oil will leak into the crankcase and mix with the fuel, causing a worse oil-burning smelly smoke out the exhaust.

Fixing a crank seal is a pain because you have to split the cases to get at it. To help prevent this problem, you want to always use proper gas and 2 stroke oil mix.

Don’t let your dirt bike sit for long periods of time either. Corrosion will build up on parts that don’t get used. The corrosion can and will eventually cause problems when you go to ride it again.

What Causes An Engine To Have White Smoke On Startup?

A 4 stroke dirt bike when started may have a little bit of white smoke coming out the exhaust on a cold start for a few seconds. This is often due to water condensation built up in the exhaust system.

If you let your dirt bike sit out overnight in a higher humidity climate and start it the following morning, there will probably be a “soft white” smoke when you first start it up. 

2002 Honda XR250R 11 Reasons Why Your Dirt Bike Is Smoking & How To Fix It

It’s nothing to worry about and will eventually go away in a few seconds or a couple minutes depending on how much moisture is in the engine and exhaust. It shouldn’t have any different smell than normal exhaust.

Coolant Burning

Burning coolant in the engine comes out as white smoke. This is usually caused by a blown head gasket

You can tell if coolant is burning by the smell. Burnt coolant will have a strong, sweet smell to it and is very distinct. 

Cyl. Head 1 11 Reasons Why Your Dirt Bike Is Smoking & How To Fix It
Blown head gasket from CR125

Spark plug symptoms from your dirt bike smoking

If your dirt bike is smoking excessively, checking the spark plug is one of the easiest steps to troubleshooting the cause. Your spark plug can sometimes tell you what the problem is or a better idea of what’s causing it.

When your dirt bike is smoking:

  • A spark plug that’s wet and oily is caused by a rich fuel mixture or oil leak.
  • A super clean spark plug is caused by a coolant leak
A wet fouled spark plug that's oily
Troubleshooting this oily wet spark plug

How Do You Fix White Smoke From A Dirt Bike?

It depends on what is causing the white smoke. There’s nothing to worry about if there’s a little bit of white smoke from condensation on first start up. 

White smoke from burning coolant is fixed by repairing any damage or warping on the cylinder head and replacing the gasket. 

Why Does My Dirt Bike Have Black Smoke?

Black smoke or dark grey smoke is generally the result of a rich air fuel mixture. A rich fuel mixture is simply when your dirt bike is getting too much fuel into the engine and not enough air or spark to properly ignite and burn the mixture efficiently.

Dirt Bike Black Smoke Out The 11 Reasons Why Your Dirt Bike Is Smoking & How To Fix It
Blackish grey smoke out the exhaust

Is the choke still on?

Whether you have a 2 stroke or 4 stroke dirt bike, if it has a carburetor then it has a choke. The choke allows more fuel to get into the engine, which is helps it start easier when cold, but this can also cause problems.

A stuck choke knob or lever is also a cause, although less common. You can test your dirt bike choke pull pulling the knob/lever on and pushing it back off.

TTR125 carburetor with a cable mounted choke
This “cable-mounted” choke is a weak point on a stock TTR125

You should be able to hear and feel a difference in how your dirt bike runs. If there’s no difference, then your choke is either stuck in the On or Off position.

Rich jetting mixture

Having a correctly jetted dirt bike is so important for many reasons, including how much it smokes, whether the engine is cold or hot.

Properly jetting the carb or tuning the fuel injection will get rid of any black smoke if everything else is working properly. When the fuel screw on a 4 stroke is opened up too much, it will allow too much fuel through.

This will make your 4 stroke harder to start when hot, and can cause black smoke, especially if the pilot jet is too big/rich.

Fuel Screw On XR250 Carb 11 Reasons Why Your Dirt Bike Is Smoking & How To Fix It
The fuel screw location on an older trail bike

Clogged air filter

Cleaning or replacing the air filter can also fix a rich fuel mixture. A dirty air filter doesn’t allow enough air to get through the engine – essentially richening the jetting.

Not only will a dirty air filter cause richer jetting, but it will lead to more engine wear and damage. The filter is the main part preventing dirty getting sucked into your engine.

If the filter is too dirty to keep sand and mud out, then it will get sucked into the engine and wear out the top-end parts much quicker. You’ll end up needing to rebuild it much sooner than if you just clean it when it gets dirty.

Dirty Air Filter causes spark plug to foul
Dirty Air Filter

Why Does My Dirt Bike Have Blue Smoke?

Blue smoke means that the engine is burning oil. This usually happens because the piston, rings, and/or cylinder is worn out of spec. Every engine burns at least a small amount of oil over time due to necessary clearances.

Excessive clearance due to wear or improper parts or installation will allow oil by and reach the combustion chamber where the fuel is being burned. It then goes out through the exhaust as blue smoke. 

Another reason why you are seeing blue smoke is because there’s oil getting into the air box. Oil gets into the air box if the oil level in the engine is too high.

Why Is There Blue Smoke On Startup?

A leaking valve seal will also cause blue smoke. This is usually just when you first start the bike.

If the smoke goes away after the engine warms up, this is a good sign that a valve seal needs to be replaced. 

Dirt Bike Blue Smoke 11 Reasons Why Your Dirt Bike Is Smoking & How To Fix It
Bluish smoke out the exhaust

Why Does My Exhaust Smoke When I Accelerate?

A worn top-end is the most common cause of exhaust smoking when accelerating. Rich jetting is also a cause of smoking when you turn the throttle. 

A worn piston, rings, or cylinder will allow oil into the combustion chamber. This oil won’t properly burn with the fuel, so it goes out the exhaust as smoke. 

Rebuilding the top-end will fix the smoking issue if the parts are worn out of tolerance. 

Why Is My Dirt Bike Steaming A Cloud of Smoke?

Did you just ride through a puddle? The engine block is hot and water splashing on it will turn to steam, which looks like smoke. 

The other reason for your bike steaming is that it is boiling over from overheating

Are 2 Stroke Dirt Bikes Supposed To Smoke?

We’ll kick this off with a solid yes and no…

A 2 stroke engine isn’t designed to purposefully smoke. Smoke coming out the exhaust means that something isn’t fully burning or there’s something that shouldn’t be burning. 

Why Does A 2 Stroke Smoke?

Most 2 strokes will inherently smoke, especially at start-up because they have a mixture of gas and oil that is being burned. The oil that doesn’t get fully burned comes out of the exhaust as smoke.

Until technology changes, even a current 2 stroke dirt bike will smoke a little bit on first start-up. This is because there’s a small puddle of residual oil at the bottom of the crankcase.

A 2 stroke dirt bike engine needs oil to keep the engine lubricated, so after you shut off the engine the excess oil runs down to the bottom of the cases and sits there until the next time you start it up. 

2 Stroke smoking a lot

When you first start your 2 stroke dirt bike, it’s naturally going to smoke a lot more. This is due to the choke adding more fuel to the mixture, and a cold engine that can’t efficiently burn all of the fuel going into the engine.

When you have a 2 stroke that’s smoking a lot even after being fully warmed up, it’s because there’s too much fuel and not enough air or compression to ignite and burn it off. This could mean your top-end might need a rebuild, or one of the simple factors I list below.

How To Reduce 2 Stroke Smoke

The 3 factors that affect the amount of smoke your 2 stroke makes are: jetting, oil premix ratio, and type of 2 stroke oil you use. 

Jetting It Right

Tuning the jet circuits can not only reduce the amount of smoke, it can increase power, throttle response, and fuel mileage. This article will show you how to tune each jet in the carb

When the jets are too big, they allow too much fuel through the carburetor and into the engine. This causes a rich air fuel mixture and results in smoke and poor engine performance.

motocross bike mods jetting
Rich Jetting Causes Spooge


Using too much oil in the premix can cause more smoke if it’s not jetted properly. The oil ratio you use should depend on what bike you ride and how you ride it. That’s what This Article is all about. 

Which Oil You Choose

The flash point of an oil makes a difference as well. You should run an oil with a higher flash point if you’re riding your 2 stroke hard in the upper RPM range. 

Using an oil with a lower flash point is great for trail riding at lower RPMs to reduce smoke. 

How Do You Know If Your 2 Stroke Is Running Lean?

A leaning running 2 stroke can have a few different symptoms. A lean bog, abrupt throttle response, and detonation are the most common signs of running lean. 

What Happens If I Put Too Much Oil In My 2 Stroke?

Putting too much oil in your premix will make it run leaner. This is because there’s less gas to burn in the mixture. 

If you put in a couple extra ounces in your tank, just pay attention to any new sounds or symptoms. If it runs like normal, there’s nothing to worry about. Just stay consistent with your ratio in the future. 

When Does Steam Happen?

Once the coolant reaches boiling point (water is 212 degrees Fahrenheit) it will turn to steam and spit out of the overflow tube. 

Overheating 11 Reasons Why Your Dirt Bike Is Smoking & How To Fix It
Steaming from getting too hot on the trail!

This happens the most often at low speed riding. For one, there might not be enough air blowing past your bike to cool it down. You might also be slipping the clutch a lot, which creates even more heat. 

Ride faster to prevent steaming?

Riding faster isn’t always possible unless you trade yourself for a better rider on your bike! 

So, learning how to more efficiently use the clutch is a great skill to learn and will keep your dirt bike running cooler!

For more help on why your dirt bike has coolant coming out the overflow read this. 

Bottom line

Your dirt bike may naturally smoke out the exhaust, but it depends on when it does it, how long, and if there’s a smell to it. If it didn’t used to smoke before and it’s doing it now, then you’ll want to look into it, although it may just be due to moisture in the engine and exhaust on a cold start-up.

The top reasons why your dirt bike is smoking:

  • It’s burning off the condensation
  • It’s a 2 stroke
  • Piston rings are worn
  • Cylinder is scored
  • Leaking valve seal
  • Blown head gasket
  • Running rich
  • Too Much Oil
  • Bad crank seal
  • Overheating
  • Water is steaming off

How to prevent catastrophic bike failures

Whether you’re trail riding on your farm or out in the desert or mountains, do you worry about having a major bike failure? Well, most of the time it can be prevented, and I want to show you how.

I put together a simple 3 step system to help prevent catastrophic dirt bike failures that could leave you stranded and with a blown up engine, and it’s based on the most common mistakes I see people making with their bike. Click here to grab your FREE guide now.

Drew Larson

Monday 9th of May 2022

Dirty air-filter can make an engine smoke too, it's like running with the choke partially on.

Kelley Fager

Wednesday 11th of May 2022

I don't normally let my air filters get that dirty, but yes, I agree that it can run rich enough to cause smoke. Thanks for reading and sharing, Drew!


Monday 28th of March 2022

I bought a venom x22 when i got it clutch had problems so i took time an learned how to fix that now ive barley rode it 100 miles and it smokes from engine maybe the exaust or vaulves but it gets got really quivk so im not sure

Kelley Fager

Tuesday 29th of March 2022

Hey Michael, sorry to hear about your bike problems. What exactly did you do to it?


Thursday 29th of April 2021

Hi I have yz450f 2009 drove it for +/- 15km and the engine locked up so I open it and found the conrod went so installed new conrod kit and timing chain the piston was new so I left it and did shims and valvetem seals.start the bike up and drove for about 500meters and it was smoking real bad exhuast was full of oil.check the oil level and it was on the full mark.please help

Kelley Fager

Thursday 29th of April 2021

Hey dale, sorry to hear about your bike troubles. It sounds like you could've overfilled it with oil. If the engine has too much oil, it can get sucked into and through the airbox from the crankcase vent hose if that's where it is.