I have recently been running champion J6C spark plugs in this motor. I just read something that had champion J68 listed as the correct plug. Could somebody tell me what the difference would be between these two plugs and which one would be better? Thanks in advance.
The original plug was Champioin J4J, Nathan, currently J4C. I believe it is still the best plug for that engine (FD-18), but many have switched to the J6C. Either will do the job, gapped at .030". The J6C is less vulnerable to fouling at low speeds and the J4C offers slightly better high speed operation.