The 1957 model, 18 hp Johnson outboard, requires an Champion J4C, or NGK B8S, gapped to .030 in.
Johnson 6hp spark plug gap
The 25 hp Johnson outboard runs a plug gap of .030 in.
.03
The 1955 model, 3 hp Johnson outboard, requires a spark plug gap of .030 in.
The spark plugs on a 1988 model, 70hp Johnson outboard, should be gapped to .030in.
The recommended plug gap for the 1972 model, 20 hp Johnson outboard is .030 in.
1984 Johnson 6 HP
The correct spark plug gap for the 1979 model, 100 hp Johnson outboard is .030 in.
.030
.030
The plug gap for a 70 Johnson would be .035 - .040.
.030 .030