Decarbonising (Decoke)

Combustion leaves carbon deposits on the piston crown, cylinder head, valves, exhaust port and silencer. Too much carbon raises compression, can cause knock or glowing hot spots, and on two-strokes clogs the exhaust port and power valve.

Decarbonising (often called a decoke) means cleaning these deposits off. On a two-stroke this is done during top-end service: scrape the piston crown and head with a soft tool, clean the exhaust port and power valve, and repack or clean the silencer.

Avoid scratching aluminium surfaces and don't let carbon flakes fall into the crankcase. Using the right oil and mixing ratio and not letting a two-stroke idle for long periods reduces carbon build-up. Fuel-system cleaners can help four-strokes but do not replace a strip-down when deposits are heavy.