What type of fuel should never be used in a two-stroke outboard engine?

Two-stroke outboard engines are designed to operate with a specific type of fuel that is typically a mixture of gasoline and oil. Using diesel fuel in a two-stroke outboard engine is inappropriate because these engines rely on the combustion characteristics of gasoline for proper function. Diesel fuel has a higher flash point and different combustion properties compared to gasoline, which can lead to poor engine performance, inefficient combustion, and potential engine damage.

Moreover, diesel engines operate on a different principle (compression ignition) than gasoline engines (spark ignition), which means that even if a two-stroke engine could take in diesel, it would not ignite properly, leading to starting issues and possible long-term harm to the engine. Thus, using diesel fuel violates the fundamental operation mode of two-stroke engines, making it a clear choice for what type of fuel should never be used in this context.