Smoke from a motorcycle's exhaust can be indicative of several issues. Here are the common causes:

**White Smoke:** This is often a sign that coolant has entered the combustion chamber, typically due to a defective cylinder head gasket or cracks in the cylinder head. It can also be normal during cold engine startup due to condensation, but it should dissipate quickly once the engine warms up[5).

**Black Smoke:** This usually indicates a rich fuel mixture, meaning there is too much fuel and not enough air in the combustion chamber. Causes include a clogged air filter, faulty fuel injectors, or carburetors that need tuning. Over-fueling or using poor-grade fuel can also lead to this issue[5).

**Blue or Grey Smoke:** This smoke is a sign that oil is entering the combustion chamber. Possible causes include worn piston rings, faulty valve guides, or a clogged PCV valve. Using the wrong type of oil can also contribute to this problem[5).

In all cases, persistent smoke from the exhaust is a sign that maintenance or repairs are necessary to prevent further engine damage and ensure safety.