Spark Plugs 1952 Johnson 25hp

[Vintage Boat Guy]

I was reading about spark plugs for my 1952 Johnson 25hp and apparently it's supposed to have NGK B8S not the NGK B6S I've been running. Would there be any consequences in running a hotter plug such as the B6S over the B8S?

 

[F_R]

There can be serious consequences if running plugs that are way too hot. That can cause engine destroying pre-ignition. But that is not likely to happen if only one heat range off, unless we were talking about high performance or race engines. Your stock Johnson certainly does not qualify as a race engine.

More to the point, a hotter plug can help burn off fouling deposits if run a lot at idle speeds. A colder plug will last longer if run a lot at high speeds. Everything is a compromise

 

[racerone]

Used to be the rule of -----J4c on motors with thermostat.------On motors without thermostat J6c-------Cross reference those if you prefer other sparkers.

 

[kbait]

B6S crosses to both J4C and J6C, so you're all good.