This is a new one to me and I have no idea how it happened. I was riding my recently restored 99 WR400 when the engine started racing for no apparent reason. The engine sounded good with no weird noises, just running at almost full throttle. I killed the bike and looked it over. I could see nothing wrong and figured I'd ride it back to the truck. However, when I tried to re-start it, it wouldn't start and felt like I had no compression. When I tore it down I found that the aluminum plate that covers the slide had somehow broken/tore off a part of it and got sucked into the intake, wedging an intake valve open. I was able to retrieve the piece of aluminum and there doesn't appear to be any serious damage, so I'm going to ride it and keep an eye on things. Anyone have that happen to you or hear of that happening? Or, any idea why it would do that?