I had a 2002 cr125 that fouled plugs every ride. I took it to a local bike shop and they leaned it out, meaning they rejetted the carb. Many will tell you to simply use better premix oil but trust me, it doesn't fix the problem. Even after leaning it out, I had to clean the plug with a wire brush after each ride, this got me about 5 rides per plug (NGK BR7ES). BR8ES is the standard MX Plug the bike calls for but a 7 can withstand more heat and lasts longer. I sold it in January 07 out of frustration and got a kdx200. Not saying the problem can't be fixed but cr125's are not jetted right out of the box for all climates of riding. The guy I sold mine to was very good with jetting and said he was used to changing the needles in the carb to suit any climate, dude I'm not a mechanic, I want to spend my time riding not wrenching. Hope this helps.