A friend has a 400EX. His exhaust header pipes glow red and the engine is firing back through the carb. Usually that means the valve timing is off or the valves need to be adjusted. But I guess it has done this since it was new and the valves are adjusted correctly. Anyone else run into this?

 

Yeah, or turn the mixture screw out a bit. The backfiring usually indicates a lean condition. As far as the pipes glowing red, it seems like a bad thing but have noticed the same myself on several quads. Also make sure your idle isn't set too high.