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 - Third Brush Generators - by Chris Pratt. While I love straightening sheet metal, cleaning, and painting old tractors, I use every excuse to avoid working on the on the electrics. I find the whole process sheer mystery. I have picked up and attempted to read every auto and farm electrics book with no improvement in the situation. They all seem to start with a chapter entitled "Theory of Electricity". After a few paragraphs I usually close the book and go back to banging out dents. A good friend and I were recently discussing our tractor electrical systems when he stated "I figure it all comes back to applying Ohms Law". At this point
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