I recently bought a '99 WR400. All stock. I have trail ridden a couple of times and ridden around the yard quite alot. While getting ready for a ride tommorrow, I was warming the engine to check my oil level in a dimly lit garage and noticed the exhaust pipe was glowing orange for the first 4-6 inches out of the head. Normal????? Or should I be looking to rebuild. All fluid levels good, water in radiator flowing.