1978 Johnson 4HP outboards Service Manual, Page 14Get this manual
ENGINE FUEL AND LUBRICANT RECOMMENDED GASOLINE: Use gasoline with the following minimum octane numbersPUMP POSTED OCTANE NUMBER Research Octane Number Most Commonly Used in the Past 86 91
Below 32 (0 Portable Tankour approximately one gallon (4 litres) gasoline into tank, add required lubricantReplace filler cap securelyThoroughly mix by shaking tankAdd balance of gasolineBuilt-in TankIn separate container mix all lubricant needed with one gallon (4 litres) or more of gasolineUse large metal filter funnelPour this mixture slowly with fuel as tank is filled
Automotive gasolines regular-leaded or leadfree meeting these minimum octane numbers may be used; however, best results will be obtained by using lead-free gasoline
A SAFETY WARNING