Why is My Motorcycle Exhaust Smoking?

Here, we take a closer look at why your motorcycle exhausts is smoking.

We have been working on bikes for over a decade and riding for another decade still. We want to use our wealth of knowledge and experience to help you figure out why your motorcycle’s exhaust is smoking and what you can do to fix it. 

A motorcycle exhaust could be smoking for many reasons, and different types of smoke could mean different things. We’ll  break down why a motorcycle exhaust smokes, how it affects your bike, and how to remedy the problem. 

The reasons for smoke from a motorcycle exhaust range from lousy fuel and a bad tune to more serious problems like mechanical issues. 

Keep reading for more information about smoking motorcycle exhausts. 

Why Might A Motorcycle Smoke?

There are a couple of different reasons why a motorcycle exhaust may be smoking. 

  1. The engine is running too rich 

This is one of the most common reasons behind smoking motorcycle exhausts. ‘Running rich’ just means that there is too much fuel and not enough air being combusted in your motorcycle’s engine. 

The air-fuel ratio can be incorrect for several reasons: The exhaust may have been replaced recently, and the bike was not correctly tuned. There may be an exhaust leak leading to more unburnt fuel in the exhaust. 

2. Coolant has leaked into the engine

Your motorcycle’s coolant can leak into the engine because of a faulty gasket or a damaged engine component. Coolant in the engine is bad for obvious reasons.

With motorcycle exhausts, you can get smoke ranging from black and white to blue and gray. Each of these colors means something different, and the fix for each will also vary accordingly. 

3. Oil has leaked into the combustion chamber 

The engine oil may have started leaking into the combustion chamber. This could be due to worn or damaged piston rings, clogged PCV valves, or worn valve seals. It is also possible that you have used the wrong engine oil for your motorcycle, which could lead to the exhaust smoking. Besides that, it is always recommended that you warm up the engine well before riding. 

How To Tell What The Issue Is By The Type And Smell Of The Smoke?

White Smoke

If you noticed white smoke coming from your motorcycle’s exhaust, it could be completely benign. In fact, it is perfectly normal for most engines to give off a bit of white smoke on a cold start. 

What you see is water vapor that is visible to the naked eye. Under normal circumstances, this type of ‘smoke’ should subside after a few minutes as the engine warms up. 

If the white smoke persists, it could signal that coolant has leaked into the combustion chamber. 

Black Smoke

Heavy black smoke coming from the engine indicates that the engine’s air-fuel ratio is not optimally tuned. The engine is probably running too rich, meaning excess unburnt fuel goes into the exhaust. It burns up because of high exhaust temperatures and comes out the other side as black smoke. 

Blue or Gray Smoke

Bluish gray smoke coming from the exhaust can be quite concerning. This type of smoke is only seen when engine oil has leaked into the combustion chamber and is burning up. It is also harder to diagnose what is causing the leakage, but nothing we can’t help you figure out. 

How To Fix Smoking Exhaust Issues?

The different types of smoke coming from your motorcycle’s exhaust have different causes. That means the fix for each is also different. Let’s see what you can do to remedy the different types of exhaust smoke. 

How To Fix White Smoke

So we know excess white smoke is due to a coolant leak in the engine. But what causes this leak? The leading causes of coolant leaks are damaged gaskets or cracked cylinder heads. Both will require you to find the damaged parts and replace or repair them ASAP. 

If there is, in fact, a coolant leak, you can also expect the coolant reservoir to be discolored. Furthermore, engine oil may also have leaked into the coolant reservoir, so definitely check for that. 

How To Fix Black Smoke

With black smoke, it is usually because the engine is running too rich. So all you have to do is retune the engine so that no more excess fuel gets into the exhaust. If your bike is carbureted, you can tune the jets to send the right amount of fuel to the combustion chamber. If the bike is fuel injected, you will need to remap the ECU. 

While you can do these yourself, we recommend getting them done professionally for the best results. 

How To Fix Blue/Gray Smoke

As we mentioned, blue smoke is usually a sign that engine oil is leaking and burning in the combustion chamber. You can easily confirm this by removing the air cleaner and looking for any engine oil that may have leaked into the air filter. Another method is to remove the spark plugs and see which cylinder exhibits abnormal fuel burning. 

In some cases, a simple oil change could be the answer to the problem of blue/gray smoke. 

Conclusion 

If you see your motorcycle exhaust smoking, note the type of smoke it emits. Different colors will mean different problems in the engine, so this information will be indispensable for figuring out where the problem originates. 

In most cases, a smoking exhaust signals that some fluids that should not be there have leaked into the combustion chamber. Be it coolant, engine oil, or excess fuel, you can pretty quickly figure out the problem and address it accordingly.

Author
Cooper Higgins

Hi, I'm Hugo, I'm a motorcycle enthusiast who’s been riding for the last 10 years. I'm passionate about all things motorcycles and started Bikes Future to help other riders make the right motorcycle moves. I ride a white Kawasaki Ninja 400, and enjoy adventure riding on country roads when I get the chance.