6 Reasons Your Motorcycle Exhaust Is Smoking – (Easy Fixes!)

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Excessive smoke from your motorcycle exhaust pipe could put you in a catastrophic situation. But it doesn’t mean something extremely bad with your motorcycle.

Sometimes, moisture condenses inside the exhaust pipe and evaporates when you start the engine.

But how do we know if this smoke is due to moisture condensation, not a major engine fault?

In this guide, we’ll discuss everything in detail. My engineering background and years of expertise in engine repairs will help you rectify the cause of excessive smoke on a motorcycle.

Black Smoke from Motorcycle Exhaust Pipe

Why Is My Motorcycle Smoking? – 6 Common Reasons!

There are several reasons why a motorcycle exhaust releases excessive smoke. The color of the smoke will help in diagnosing the cause.

Generally, white smoke comes out from your motorcycle exhaust in cold weather. It happens because of the moisture condensation inside the exhaust pipe. When you start the engine, the moisture evaporates. It automatically goes when you ride for a few miles.

But, if it doesn’t go automatically, it’s alarming. There might be some major fault with your motorcycle.

Let’s look at the various reasons for smoking motorcycle exhaust.

1. The engine is running too rich

The most common reason for smoking exhaust is your engine running too rich. It indicates incomplete combustion of fuel in the combustion chamber.

As you know, to burn any hydrocarbons, the presence of oxygen is very important.

Look at the chemical reaction that happens inside the combustion chamber:

Combustion Reaction

For the complete burning of 2 moles of gasoline, 25 moles of oxygen is required. But, this is a theoretical value.

So, engineers performed various practicals and found 14.7:1 is the perfect ratio for complete combustion.

That’s why engine manufacturers recommend a 14.7:1 ratio (stoichiometric ratio) for gasoline engines.

If you supply a mixture that is too rich to the combustion chamber, some parts of hydrocarbons come unburned, resulting in black smoke from the exhaust pipe.

Causes: The clogged air filter is the primary cause of the air-fuel mixture being too rich. If you haven’t changed/cleaned your air filter in the last six months, the pores might have been blocked, which results in a lesser oxygen supply to the engine.

Other reasons, such as faulty O2 sensors, bad fuel injectors, outdated ECU firmware, and incorrect carburetor tunning, could also lead to a rich air-fuel mixture supply to the engine.

Symptoms: If your engine runs too rich, you’ll see black smoke from the motorcycle exhaust. You’ll also get lesser mileage when a mixture that is too rich in A/F is supplied.

How to fix: If black smoke comes from your motorcycle exhaust, first replace the air filter and tune the carburetor (if your motorcycle has one). Most probably, replacing the air filter will fix the issue.

If it has a fuel injector, please inspect the O2 sensor with an OBD2 scanner. I advise you to visit a mechanic garage and get the ECU tuned.

2. Oil leakage to the combustion chamber

During the power stroke, the combustion chamber temperature goes between 1500°C to 2000°C.

Engine oil helps in heat dissipation and lubrication, keeping the engine cool. But, if the oil finds a path to the combustion chamber, it burns with fuel and creates bluish-gray smoke.

So, the oil leakage to the combustion chamber is another reason your motorcycle exhaust is smoking. Generally, you will see black/blue smoke from the motorcycle exhaust.

Oil leaking to combustion chamber

Causes: The worn piston ring, blown cylinder head gasket, and cracked piston are the main reasons for oil leakage to the combustion chamber. If your motorcycle is too old, the piston rings are probably worn.

Symptoms: You’ll see black/blue smoke from the exhaust pipe.

How to fix: Perform a cylinder leak-down test, check if pressure leaks from the crankcase, and replace the piston rings.

3. Engine oil problems

Bad quality and excess engine oil could also create smoking problems on motorcycles. If you have filled bad quality or expired engine oil, it could be why your motorcycle exhaust is smoking.

Causes: If you put too much oil into the engine, it will find a path to escape. Due to high exhaust temperatures, the excess oil will burn and cause gray smoke from the exhaust.

Symptoms: You’ll see black/gray smoke from your exhaust pipe. Also, too much oil will cause hard gear shifting.

How to fix: Drain all the engine oil and refill it with the manufacturer’s recommended oil in the right quantity.

4. Moisture condensation

As mentioned, moisture condensation is the most common reason for smoking motorcycle exhaust. If you live in cold weather, the moisture condenses inside the exhaust pipe, evaporating when the motorcycle engine temperature increases.

Causes: The leading causes are cold weather, flooded motorcycles, and water inside the exhaust pipe.

Symptoms: You’ll see white smoke coming out from the exhaust pipe, and it goes away after riding a few miles.

How to fix: Nothing is required. Just ride your motorcycle for a few miles to evaporate moisture from the exhaust valve.

5. Coolant leakage

Higher engine size motorcycles are water-cooled. The water is passed through cylinder jackets to maintain the optimal temperature.

However, if the coolant finds its way into the combustion chamber, it causes smoking exhaust.

Causes: Coolant leakage happens due to a cracked cylinder head, defective gasket, or manufacturing defects.

Symptoms: Coolant leakage can reduce the bike’s performance and mileage. Also, black and blue smoke will come out from the motorcycle exhaust.

How to fix: Take your motorcycle to a mechanic garage. Because it requires leak-down tests and other repair work done by skilled mechanics.

6. Aftermarket exhaust

The stock exhaust system has a catalytic converter that filters harmful gases before emitting them into the environment.

If you’ve installed aftermarket exhaust with no catalytic converter, this could be another reason why your motorcycle is smoking.

Click here to read my other guide on the effect of decating a motorcycle exhaust. I’ve explained the advantages and disadvantages of removing the catalytic converter from the exhaust.

Causes: Free flow exhaust system has no catalytic converter and passes all harmful gases to the environment.

Symptoms: The exhaust gases will smell very toxic.

How to fix: Install stock (OEM) exhaust that comes with your motorcycle.

Also Read: Do Motorcycles Need Smog Checks?

Why Is My Motorcycle Exhaust Releasing White Smoke When Cold?

If the weather is too cold, the moisture condenses inside the exhaust pipe and various engine parts.

When you start the motorcycle, this moisture condenses into water vapors and releases through the exhaust pipe, resulting in white smoke.

It automatically turns normal when you ride for a few minutes.

Why Is Black Smoke Coming Out From My Motorcycle Exhaust?

The most common reason is too rich air-fuel mixture. It happens due to a clogged air filter, inaccurate carburetor tuning, faulty O2 sensor, and bad ECU programming. You should visit a professional mechanic garage for carburetor tunning and ECU programming.

Why Is White Smoke Coming Out From Motorcycle Exhaust When Accelerating?

If you washed or parked your motorcycle in the rain, the water must have gone into the exhaust pipe. When you accelerate the motorcycle, this water evaporates into steam and is expelled on the exhaust tip.


If your motorcycle is smoking, see the smoke and note its color. Different smoking color has different meanings. White smoke indicates the vaporization of moisture, while black smoke indicates a too-rich air-fuel mixture. Read the above guide to fix the issue.

I hope this guide helped you. Don’t forget to share your valuable feedback in the comment box.

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