Two-stroke mix ratio
The proportion of petrol to two-stroke oil that a combustion chainsaw runs on, expressed as a ratio such as 50:1 or 40:1. The engine has no separate oil sump, so this mixture is the only lubrication the crankshaft and piston receive.
Always use the ratio in your own manual: modern saws commonly specify 50:1 with a quality two-stroke oil, while some older or air-cooled designs call for richer mixes. Getting it wrong is expensive in both directions — too little oil seizes the engine, too much fouls the plug, coats the exhaust and costs power. Mix in a clean, marked can rather than by eye, and use fresh fuel, because pump petrol with ethanol separates and degrades within weeks; premixed alkylate fuel avoids that entirely and burns much cleaner. Never run straight petrol, even briefly.