Hotter plug…
Recommended if you idle a lot.
Cooler plug if you run fast a lot.
Champion Spark Plugs Decoded
Discover what the combination of letters and numbers assigned to every Champion spark plug indicates about its design.www.championautoparts.com
Or 1950 when every angler kept a least one spare set of plugs in their tackle box. One quart of Gulf motor oil to 5 gallons of gas was the mix for my motors for years. Never owned a 50:1 motor until I bought a new Mercury 850 in 1977. In 20 some years only changed the plugs (surface gap) once that I remember.Spark plugs change with fuel burn characteristics.----Fuel is now different than what I remember.----Does not smell the same as it did in 1968