Nothing like a 500 with a stuck throttle to get your attention!! I should have added that, as other have pointed out, a stuck throttle cable will also do this, but in that situation the kill button should work (I know that lean it will not). I have not encountered the KX throttle sticking (yet?) but it certanly can happen to any bike. As a check, before I ride I always snap the throttle and listen to hear the sound of the carb slide bottoming with a nice solid clear "click". Repeat with the bars turned full lock. If it does not sound solid, then some repairs or lube may be in order. In the old days we used to lockwire the cable into the top of the carb adjuster so it couldn't jump out, but old euro bikes were really prone to that. Haven't done the KX. If you don't ride with barkbusters, a small RHS layover can jam the plastic throttle tube against the bar end making it stick, but at least then you can force it closed it by hand. Cam.