I have a 2002 Mercury 115 hp, 2+2, 2 stroke outboard. After putting premium gas and iridiums in my small mowers (along with my regularly added Sea Foam) after your suggestion worked so well I thought I'd try them in my outboard since the lower 2 cylinders don't generate power at low rpms and as a result the plugs, although firing, aren't causing the cylinders to come up to the temperature required to burn off contaminants on the plug insulators.
Pulled up my NGK catalog, and somewhere around page 268 (recollecting) I got into the "IX" (Iridium) plugs section and cross referenced my OEM recommended plugs to IX. In the process I decided to go to a hotter plug too so I dropped down from 8 to 6 on the heat range. I was already using 91 octane gasoline as fuel so I didn't need to change that....engine is rated for 87 octane minimum but with 20-22* BTDC at WOT, pre-ignition could be a problem anyway so I already had that addressed.
Water testing revealed starts faster than you could operate the key switch and contrary to reports of rough idling with these engines, with the engine tilted up slightly so that any un-ignited fuel wouldn't puddle in spark plug area, idling around in the no-wake zone and all, you could have placed a full glass of water on the engine and not spilled a drop.
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Today's Featured Article - Earthmaster Project Progress Just a little update on my Earthmaster......it's back from the dead! I pulled the head, and soaked the stuck valves with mystery oil overnight, re-installed the head, and bingo, the compression returned. But alas, my carb foiled me again, it would fire a second then flood out. After numerous dead ends for a replacement carb, I went to work fixing mine.I soldered new floats on the float arm, they came from an old motorcycle carb, replaced the packing on the throttle shaft with o-rings, cut new ga
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