Correct Spark Plugs for '58 Evinrude 18hp

[RSchendel]

I added this question to a different post, but should have created a new one.

'58 Evinrude 18hp 15024

Original Parts Manual specifies Champion J6J.
New substitute for J6J is J6C according to Champion site.
Champion Application Guide indicates J8C.

Other posts on this site and others specify J4C. My motor currently has J4Cs installed, but they are a bit black. I have no idea how long they have been installed as I just acquired the outboard.

I am inclined to try the J6C as the heat range is between the two others.

Also, is there any harm in using Resistor plugs to prevent interference with my depth finder?

 

[jimdd810]

Re: Correct Spark Plugs for '58 Evinrude 18hp

i beleive the correct plug is the j4c. Put in a new set of plugs and see how she runs. Hotter plugs can damage an engine. If they turn black again then the motor is running to rich. Might be time for a carb overhaul.