My lil bro's 96 RM 125 won't run on the cheap BR8es's and it's jetted properly I know I did it myself must of gone threw a dozen of those cheap plugs trying to find out what was going on. It would foul them out in like half an hour of riding, but put one of those expensive NGK Racing plugs in it and it's run excellent ever since. My '04 KX 125 is using that plug now, the main reason they run those plugs is the harmonic hum of the motor is breaking off the electrodes. Just compare it to a normal BR8EG or something and you can see how much more beefier it is. You can get them for the RM's threw parker yamaha for alot cheaper than $26 a plug. The one for the KX is new, so i'm having trouble finding them cheaply good thing my local kawie dealer sells them to me just alittle bit above his cost so they are like $22.