Stihl gasoline-engine chain saws are powered by two-cycle motors that operate on a combination of gasoline and lubricating oil. The oil and gas must be blended in the appropriate proportions or motor operation will suffer. Attempting to follow fuel-mixing instructions could also lead to piston seizing and other permanent, costly engine damage.
The gas-oil mix for a Stihl chain saw is 50 to1. That is equivalent to 2.5 fluid oz of low ash two-cycle engine oil per 1 gallon of mid-grade gasoline with an 89 octane rating and no more than 10 percent ethanol. When mixing, pour the oil into the container and then add the gasoline. Shake well to combine them thoroughly.