Either will work. The J4C (replaced the J4J) is a bit cooler. . .suitable for high speed operation, and the J6C is a bit hotter. . .suitable for idle/trolling.
Either will work. The J4C (replaced the J4J) is a bit cooler. . .suitable for high speed operation, and the J6C is a bit hotter. . .suitable for idle/trolling.
On this subject, I've often wondered if the J6C was used for sustained high speed operation (or vice versa - using the J4C for low speed), would it harm the engine, or just not be as good in performance as if the other plug was chosen.