A 50/1 fuel ratio is required for any Johnson outboard motor developed after 1964. With the exception of a few fishing motors made before 1955, which employ a 16/1 ratio, motors built before that year require a 32/1 ratio.
Two-cycle engines are used in Johnson outboard motors. Lubrication is provided by a mixture of fuel and oil in these engines. The crankcase acts as a pressurisation chamber, allowing the fuel mixture to pass through the piston rings and into the ignition chamber. This supplies the spark plug with gasoline and leaves a thin film of lubricating oil on the cylinder walls. Due to a lack of lubrication, operating with an excessively high fuel-to-oil ratio causes early wear on the parts.
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