Have you tried turning the idle screw? turn it all the way in, for the plugs blowing I amd told that it's common, and I'm pretty much having the same problem. What fuel:oil mix are you using? if it's 32:1 or leaner consider jetting. Hope this helps.
You shouldn't be fouling plugs, but that could be a lot of things. 2-stroke MX engines shouldn't really idle much. Your bike could be fouling plugs because it's jetted improperly. It could also be fouling plugs because of yoru riding style. 125's don't like to be lugged around at low speeds in a high gear. They don't like to be crused around at low speeds for extended periods of time. I like a few seconds of idle on my 2-strokes. This will give the best throttle response, provide some (but still minimal) engine braking going into turns, and make the bike less likely to foul plugs when running at low speeds.
I am new to this particular bike and can't seem to find the idle screw. I have been reading around the forums and someone with a 94 125 had to turn the choke knob. I did this but it didn't help. I am running 50:1 right now. THanks