for best preformance of your motor use the recommended plug specified by the manufacturer. venturing into different territory, can cause irrepairable damage. this are recommended, for Johnson/Evinrudes.
Ignition systems on outboards are designed around a specific spark plug and you should not mess with a proven system. There are very few instances where a different plug can help but it generally involves the way you operate the engine more than anything else. Spark plugs are like fishing lures. Fishing lures catch more fisherman than fish.
I was told by an old timey OMC mechanic that the wrong plug can cause ignition/engine damage so why tempt fate to gain an imperceptable amount of power.
I really doubt any plug would increase HP to where you could notice and it may thrash your motor, JC's are cheap, stick with them.
I would use the standard plug with a few exceptions. Changing the plug to a different type is not going to boost power. Gapping different will also not make any different either.
The one exception is if the motor is used only for trolling or slow speed operation then you can go 1 or 2 heat ranges higher. Again it will not boost power but it can help it to burn off the 2 stroke oil the same way the standard plug would do at WOT. Also use the products like OMC Engine tuner to remove excess carbon and free the rings for cleaner running and higher compression. You will have to change the plugs after done so use some old plugs while useing engine tuner and when completed put in a new set.
