Fire up your Yamaha on the first twist of the key with Champion RA8HC Spark Plugs (810 10388)-a drop-in upgrade that keeps two-stroke and small four-stroke outboards lighting clean and strong. Champion pairs a copper-core center electrode with a nickel-alloy ground strap, pulling heat away from the tip so it resists fouling at long trolling speeds yet stays hot enough for quick holeshots.. Cut to a 12 mm thread with a 5/8-inch (16 mm) hex, the RA8HC screws straight into many Yamaha 40-60 HP classics and portable models without adapters. A factory-set 0.028-inch gap and built-in resistor tame radio noise that can scramble your GPS or digital tach, while corrugated ribs on the porcelain insulator stop flash-over in damp weather.. Why these plugs earn space in your spares box. Cooler, cleaner burn: copper core sheds heat for longer life and steadier idle.. Marine-ready build: nickel electrodes shrug off salt and leaded fuel additives.. Plug-and-play fit: 12 mm threads, gasket seat, and re