Nah...stick with NGK's for a Japanese model...trying to cross over Euro plugs to a Jap moped or vice versa is a real headache and never seems to work.
The heat ranges are just...well...different.
Plug fouling is usually the sign of an overrich mixture, which prolly is cutting into your performance as well - check that first, and if that doesn't help....you can try going up a heat range on the plug, but that's really risky if you don't know exactly what you are doing.
See if you can lean your mixture some, and do a couple of "plug chops" (running flat out for a while and then hitting the kill switch without throttling down) - pull the plug and look at it....should have a nice, tan/coffee kind of color....if it's whitish, yer too lean, if it's real dark, yer too rich.
If you can get the mix just right, not only will you not be fouling plugs, you should find a small increase in performance as well.