Which engine oil in Suzuki RM 250 1991 and how much?

It’ll be a two-stroke engine in the year of construction. So you need an oil that is suitable for two-stroke engines. You have to look or ask in the building market or car accessories store. As a rule, this is directly on the packaging, 2 clock motor oil or 2 clock universal oil.

How much oil you need to add depends on the mixing ratio of the engine. As oil and gasoline are burned at the two-strokeer. The most common mixing ratio is 1:50. That means 50 parts of gasoline comes 1 part of two-stroke oil. That would be 100 ml of oil for 5 liters of gasoline. The mixing ratio for the engine of the Susi should be in the manual, provided that there is. Otherwise, google or ask in the car/motorcycle accessory store or workshop.