I ride a ZXR250, and was going down the street in first gear, revving at 18,000 (which I rarely do) and when I fully closed the throttle It went into neutral, the oil hasn't been changed for about 5000 km, what could It be? It only has 20,000km on the clock which isn't a lot for these bikes. Should be able to go around the clock at least once on original engine parts.