Correct spark plugs for a 1972 20 hp Johnson

[sbassman]

I have recently purchased a 1972 20 hp Johnson outboard (20R-72R). The plugs that were in it were a Champion JC8. Is this right. If it is not right has it done any damage to the motor I ran it at the lake for about 10 min. I have a 1969 20 hp Johnson and it ran J4C Champion plugs. What are the correct plugs for my 1972 Johnson. Thanks in advance

[Vic.S]

'72 20hp J4C gapped 0.030" same as the '69.
Damaged it in 10 mins be amazed if you did but they are too hot.

[sbassman]

thank you I appreciate it

[lindy46]

If you troll alot, you can run J6C. They will be less apt to foul out. That was the problem I had with my 1972 18hp Rude with J4C's - went to J6C and solved the fouling problem.