hi, i run a bike club and we have various moto-x bikes. eg 2 x cr125s 2004&2005, kx85s 2003&2005 two ttr125s and a pw80. when we got the bikes new all the 2-strokes needed plugs after about 1hr riding because they got black and fouled. the reason was that our track was quite tight so the revs were quite low at times causing fouling. this was fixed by putting NGK B8ES or BR8ES plugs in them. they are not racing plugs but they last for ages and they don't cost as much. also we run all our bikes on a mix of 5 LTS of petrol to 100 ML of oil. this has worked for us over the years and we don't seem to have this prob any more. hope this helps.