I have a 99 KX 250 that starts to cut out sporadically after about 5 minutes of riding. It sputters at both low and high rpms, and once in a while it will even die and it takes a few minutes to get it started again. Sometimes it will accelerate strongly through all the gears, but it will lose it's strength again at any moment. When it is started cold, it will usually run fine for about 5 minutes. The engine does not feel any hotter than normal.
I've changed out the plug, checked the air filter and put brand new gas in it, to no avail. Any thoughts before I start pulling it apart? I really don't know what I'm looking for, but I figure it couldn't hurt to clean out the carb. I have not performed much maintenance on it since I bought it two years ago (besides changing the filters and fluids, of course).