I have a 1974 mercury 650 with thunderbolt ignition and was wondering what is the right spark plug is the right one for this motor? the ones in it are just flat not like ones in cars,smother small engine are these right? thanks
The engine and ignition system have to be designed for them..... They are just a spark plug, like any other.... Want more 'performance'? Make sure the prop you have is letting the engine spin at the top end of the recommended max revs....