I have a 91 CR500 engine in a 06 CR250R chassis. It was put together by someone else and I bought it like it is now, so Idk whats all inside, but it seems to do alright. Im use to 2 strokes and am use to the feel and sound of them, but ever sense I bought this CR500AF it has made a heavy engine noise. Im talkin I can barely hear the powercore silencer because the engine noise is so loud. Is this normal? Do 500s just have a ton of engine noise, or is it time for a rebuild on that motor? If u guys need a better understanding, Ill try to upload a video with good sound quality so you can understand a little better.