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I looked up a plug for my 1969 25hp Johnson on the Champion Spark plug website. It shows that I should be using J8C. Crowley Marine shows J4C. Anyone know which one works best ????
Rule used to be J6J ( now J6C ) without thermostat in the motor.-----Motors with thermostat from the factory were J4J ( now J4C ) ----Is the thermostat installed on yours and is it working properly ?---They are often stuck open.------Any other running issues ?----Does spark jump a gap of 5/16" on a tester ?
Champion plug charts will tell you to use anything that fits the hole. Don't believe them. That is a high performance, high revving motor, designed for J4J (C) plugs. J8 is way too hot, and can cause pre-ignition and piston destruction. JMHO.
I have not checked/tested the thermostat or spark yet. did do a compression test cold before I bought it...127,128lbs. The head gasket, exhaust gasket and thermostat gasket look to have been replaced at one time. Pumps water good. Once started and warmed up she runs out darn good for a 50 year old. I hit 28.1 mph on my gps yesterday running on my 14' Alumacraft. Would like to try an 11" pitch prop if anyones got one laying around. And would like to try to get her to idle a little smoother/slower but its pretty good right now...
The correct autolite plug was an A-21-X, which is a 353 under their new numbering system.
A 303 equates to the autolite A-3-X under their old system. One heat range hotter than recommended.
You have about the best outboard ever made in that power range, I have a couple 20's (see recent posts) The 22 CID engine is tough but use a lot of gas. I use NGK B7HS with no problems at all.
Yes, I wondered how to tighten steering also. Look under the lower cowling above the steering bracket, there is a screw there. You have to look up from below to see it.
