keep fouling plugs...need help

http://www.dirtrider.net/forums3/showthread.php?t=42618
First, you have a thread that is already started on this subject.
So, at the top of this forum is a "sticky", that thread covers jetting and how to determine whether your bike is lean or rich and in which part of the jetting needs to be adjusted. Every bike is different and there is no set figures to make your bike perfect. You might be able to get a base line but that requires more information. Read thru the "jetting" thread and buy several jets for your bike the next time you are in a shop. It takes time to jet a bike the first time. After you've done it, it is really very easy. Yamaha's web site has great diagrams and part numbers for the available jets and needles for your bike as well as the stock ones.
You'll need to remove your carb, remove the float bowl and float, and then the jets. The size of the jet is stamped into the brass. Smaller number less fuel, larger number more fuel. Following the guide, you will get it right and you will always know how from then on. Really, it is fairly easy, it is just time consuming.
http://ericgorr.com/techarticles/carbtuning.html

You know, not to sound like its a FOR SURE kind of fix, but my girlfriend has a YZ125 and she kept on fouling plugs and fouling plugs, and at the time and before I was using this WALMART 2stroke oil, after I switched to some good stuff (Maxima high rpm racing oil is what I use now), she hasnt fouled a plug since.

Plus it gives off a good racing smell ;)