ORIGINAL: britbrat
My experience is somewhat different. While I have certainly had a few engines that needed specific plug types, I have generally found that most sport engines running on 10% nitro are not at all fussy as to the type of plug. Most of my engines can't tell the difference between an OS #3, #8, Tower generic plug, or even a Fox idle-bar plug.
I used to feel this way too. However, an experience I had in the '80s with my K&B 3.5 outboard changed my thinking. I used to race it. I had always used K&B 1S plugs. I didn't want to be bothered with high nitro, so even when I raced, it was with 15% fuel. Anyway, I got out of racing, but still had the boat. One day I decided to take it out to the lake for fun. At that time I was using Fox idle bar plugs on my plane engines, so I just stuck one of those in the outboard. When I got it on the water, no matter what I did I could not get the engine to run like I knew it should. I knew the boat trim was right, and I tried leaning the engine out as much as I could, but it was still a dog. I finally tried installing a K&B 1S plug and the engine came to life. I'm not saying that the Fox wasn't a good plug, this is more to point out that different plugs will result in different performance. That experience convinced me that I should be more careful with plug selection.