I've solved a couple of other guy's engine problems with them, but haven't needed to use them myself in the last few years. Got back into flying after a long layoff and have a supply that just may never be needed.

I've never experienced them costing RPM. Never heard that they would, and am guessing the idea came from sometime when one didn't suit the fuel/engine. That happens with all plugs. Seems that the Fox idlebars ran just like the Fox regulars, and K&B did the same.