Any Johnson outboard motor built since 1964 requires a 50/1 fuel ratio. Motors built prior to that date require a 32/1 ratio, with the exception of a few fishing motors built prior to 1955 that use a 16/1 ratio.
Johnson outboard motors are two-cycle engines. These engines use a fuel and oil mix to provide lubrication. The crankcase serves as a pressurization chamber that forces the fuel mix past the piston rings into the ignition chamber. This provides the fuel that the spark plug ignites, and leaves a thin film of lubricating oil on the cylinder walls. Operating with a fuel-to-oil ratio that is too high causes premature wear on the parts due to a lack of lubrication.