1975 Johnson 4HP 4R75, 4W75 Outboards Service Manual, Page 11Get this manual
ENGINE FUEL AND LUBRICANT RECOMMENDED GASOLINE: Use gasoline with the following minimum octane numbersRESEARCH OCTANE NUMBER Most commonly used in the past PUMP POSTED OCTANE NONumber posted on gasoline pumps since September 1973 91
Built-in TankIn separate container mix all lubricant needed with one gallon or more of gasolineUse large filter funnelPour this mixture slowly with fuel as tank is filled
IlIA SAFETY WARNING
Gasoline is extremely flammable and highly explosive under certain conditionsAlways stop engine, and do not smoke or allow open flames or spark near the boat when refueling or changing fuel tanksFUEL MIXTURE part Lubricant to 50 parts Gasoline OR: (6 GalTank) pint lubricant to gallons (5 Imperial) of gaSOline (3 GalTank) 1 pint lubricant to gallons (2-1 Imperial) of gaSOline IMPORTANT: Additive compounds such as "tune-up" compounds, "tonics," "friction reducing" compounds, etc are unnecessary and are not recommendedThe use of OMC engine cleaner, OMC rust preventive oil and OMC 2+4 Fuel Conditioner is recommended