Bob, 3W are a very efficient 2C engines, well ported, well made, well field proved.PERIOD. About spark plugs, please don't try to reinvent the wheel NGK are the best spark plugs availables at reasonable price. I`m also in the world of go-cart racing and outboard racing, and every engine is a particular requirements. For example, there are by 34$ special spark plug (NGK) for carting racing, but also the 4$ plug will work but only the first two or three laps, and after that the heat start to build up and oil deposits too, engine start loosing power and every laps time goes up, but hey run at 13000RPMS wow is like a glow plug. In our case a 3W is a torque engine schneuler and boost ported like modern bikes and race outboard but always is but, you should have your best power range(torque) between 6500 and 7500RPMS engine can goes more up but is really a waste if you dont need that(stock engine not TOC engines) also 3W engines have a relative high compression, and as air fuel mix is more dense inside combustion chamber, more difficult for the spark to JUMP the electrode, but for this reason the have a well and strong ignition which deliver a strong pulse.The gap that our friends recommend .018 to .025 is OK Remember this engines use a lower oil ratio than conventional two cycles engines so if you add this with a well ported engine and good compression you will find a much better and easy to explode mixture and at the right spark time. What you have to be carefully with the gap is the oil quality are you using and of course the right ratio recommended. Be worried about your engine idles OK instead to reach full WOT rpms, small gaps are much easyest to cause problems at idling specially with high oil ratios and junk oils.

Hope this helps and please guys correct me if I`m wrong