♻️Catalytic converter

How it works

The catalytic converter is the emissions device fitted in the exhaust system of recent four-stroke motorcycles. Inside it sits a ceramic honeycomb coated with precious metals (platinum, palladium, rhodium) which, once hot, chemically convert much of the toxic gas (carbon monoxide, unburnt hydrocarbons, oxides of nitrogen) into far less harmful ones. It only works at temperature, and it assumes the combustion feeding it is healthy. Its worst enemy is a mixture that stays too rich, or a persistent misfire: the surplus of unburnt fuel finishes burning inside the converter, drives its temperature through the roof and can melt the honeycomb until it crumbles. Once melted it breaks up and blocks the exhaust, which shows up as power that has gone missing, an engine that bogs down and dies, and a rattle like loose gravel in the pipe; persistent black smoke and a sharper smell often come with it. The key point is that a converter never destroys itself. Fix the engine-side cause first (rich running, the lambda sensor, injectors, ignition), then fit the new part, otherwise that one melts too. Diagnosis and replacement are shop work, the part is expensive and emissions are regulated: on a road-legal bike you do not delete the converter.

Maintenance tips

• ✓Deal with black smoke or an over-rich mixture straight away: running rich for any length of time overheats the converter and kills it.
• ✓Fix the engine-side cause (rich running, lambda sensor, misfires) BEFORE you replace a converter, or the new one will melt just the same.
• ✓Fill up with good-quality fuel and steer clear of dubious additives, which can poison the precious metals coating the honeycomb.
• ✓Never delete the converter on a road-legal bike: it is illegal on public roads and it will fail you at the roadworthiness test.