• Blue-tinged white or grey smoke: Your engine is burning oil.
• Thick, persistent white smoke: The engine is burning coolant, which is less common for air-cooled bikes but can happen if the bike has a liquid-cooled head.
• Black smoke: The bike is running with a fuel-rich mixture, which is unlikely to cause “a lot of smoke” but is still a possibility. 

• What they do: Valve seals and guides prevent oil that lubricates the valve stems from leaking into the combustion chamber.
• Key symptom: You see a puff of blue smoke when starting the cold engine in the morning, which then clears up. You might also notice smoke when you decelerate and then get back on the throttle. This happens because oil seeps past the worn seals into the cylinder when the engine is sitting or is under high vacuum.
• How to test: A leak-down test is the best way to confirm this diagnosis. 

• What they do: Piston rings seal the gap between the piston and cylinder wall, preventing combustion gases from leaking past the piston into the crankcase (known as “blow-by”). A scraper ring also prevents oil from moving up into the combustion chamber.
• Key symptom: The bike smokes consistently, especially under acceleration, and its performance has decreased. You will also experience increased oil consumption.
• How to test: A compression test can identify worn rings. A simple check is to open the oil filler cap while the engine is running and see if puffs of air are escaping. 

1. Confirm the smoke color and timing. Observe when the smoke occurs—on cold startup, acceleration, or constantly—to better diagnose the issue. Also, check your oil level regularly to see if it is decreasing.
2. Perform diagnostic tests. You can take your bike to a mechanic for a leak-down and compression test to accurately pinpoint the internal problem.
3. Plan for repairs.
   • Minor issue: If it’s just minor valve seal seepage, some riders choose to manage it by simply topping up the oil more frequently.
   • Serious issue: For serious smoking, worn rings or guides require a top-end engine rebuild. The YX600 is an air-cooled motor, which can be simpler to rebuild than a liquid-cooled engine. This involves removing the engine’s top end to replace the worn components. 

https://www.topspeed.com/motorcycles/motorcycle-news/why-is-my-motorcycle-smoking

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. 

https://motoxtasy.com/why-is-motorcycle-smoking-causes-solutions/