Picked up a 2002 KDX 200 last weekend. The bike was super clean. Its bone stock and doesn't seem to be abused. I was told it has about 500 miles on it. I started it and have ridden it for a short time and it runs great. However, when it is idling, the engine chatters as if the piston knocking. It did not sound right to me. I have had a 125 two stroke in the past and it did not make this noise, but I know the KDX has a slightly different engine design from a motocrosser. I plan on pulling the top end over the winter just to be safe, but I was just wondering if this was a characteristic of the KDX or if it is a problem. I had a friend who races and he told me of a guy who raced a KX500 that always rattled and knocked as if it was going to explode, but instead it always ran great with no problems. So I was just wondering. Any help would be appreciated.