50:1 gas to oil ratio
The 18 hp Mercury outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.
The 1971 model, 18 hp Evinrude outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.
Your 1958 Johnson uses a 24 to 1 mixture.
You have to check with the serial number that is on the engine.
A 1960 model, 18 hp Evinrude outboard requires a 24:1 ratio.
50 to 1
The fuel tank capacity is 18 gallons
24:1 Manufacturers recommendation. You can go up to 32:1 with the newer oils available. The FD-12 is a 1958.
18 gallons ( U.S. ) / 68 liters
About 18 inches behind the coolant tank that sits next to your battery.
10 volts minimum,18 max.
The 1957 model, 18 hp Johnson outboard, requires an Champion J4C, or NGK B8S, gapped to .030 in.