Burning smell while riding

A burning smell appears while riding or at a standstill with the engine hot. Depending on its nature, it points the diagnosis: an acrid 'friction' or burnt-lining smell after a hill or a lot of slipping suggests the clutch; a smell of hot plastic or rubber, sometimes with a wisp of smoke, suggests a brake staying on or oil dripping onto the hot exhaust; a sharp electrical smell (hot insulation) is the most worrying because it signals a harness or component overheating — a fire risk. Some of these causes are harmless and easy to fix (spilled oil burning off, a clutch that overheated briefly); others require stopping immediately. If there's a strong electrical smell, smoke or abnormal heat: switch off the ignition and have it checked before setting off again.