Exhaust smoke colour: what it tells you about the engine

Smoke from the muffler is the cheapest diagnostic you have: its colour often reveals a problem before it becomes a major failure. Judge it on a warm engine, not just a cold one.

• Warm the engine to operating temperature, then watch the exhaust at idle and when you snap the throttle open.
• Thin white vapour that vanishes quickly, especially in cold weather, is condensation. It is normal until the engine warms up.
• Thick white smoke with a sweetish smell that does not clear after warm-up can mean coolant is entering the cylinder. Stop riding and go to a workshop.
• Bluish smoke means oil is burning: worn rings or valve stem seals. Check the oil level and compare it with your last reading.
• Black smoke and a smell of fuel mean the mixture is too rich: a dirty air filter, or a carburettor or injection fault. Check the filter yourself, but leave the fuel system to a mechanic.