What is the gas oil ratio for a 1997 2 stroke 25hp Yamaha outboard?

Most two stroke engines in general run on a 50:1 ratio (Gasoline to oil). This means 0.5 liters of oil to 25 liters of fuel. Modern two strokes usually have an oil pump and inject the oil into the fuel at different rates according to rpm, however the pre-mixing of the fuel oil will still work fine in these engines. (However, you must disable the alarm for an empty tank if you do not use the automatic lube system on these engines) On Two Stroke Mercury engines pre-mixing is a good idea as the oil pump drives are prone to failure if the engine gets to hot!