I used to think spark plugs were “one size fits all.” I learned the hard way that picking the wrong ones can cause rough starts, poor idling, or even engine damage.
The first thing I check is the manufacturer’s manual for my outboard. Mercury, Johnson, and Yamaha all have specific plug recommendations. I also pay attention to the heat range — too hot and you risk pre-ignition, too cold and you’ll foul the plug quickly.
I usually carry a spare set of plugs onboard, because I’ve had trips cut short by a single bad plug. I’ve also learned to gap them myself with a simple gauge instead of trusting they’re ready out of the box.
Ever since I started being picky about spark plugs, my outboard has run smoother, started faster, and burned fuel more efficiently. It’s one of those small details that makes a huge difference.