What Is the Proper Fuel-Oil Mixture for a Mercury 15-Hp Outboard?

Two-stroke 15-horsepower Mercury outboard motors require a 50:1 fuel-to-oil mixture. However, not all 15-horsepower Mercury outboards are two-stroke engines; many newer models are four-stroke designs. Four-stroke engines have a lubrication system similar to a car, with a separate oil reserve, and don't use pre-mixed fuels.