Why is my 2003 Yamaha Big Bear 400 backfiring through the carberator and header pipe glowing red. It just started doing this all of a sudden. It's all stock with only 465 miles on it. Help!

That sounds like it is running too lean. You may need some carb adjustments to account for your altitude.

Definitely DO NOT run this engine in its present condition. Sounds like you have developed a air leak somewhere, you shouldn't have to rejet your carb just "all of a sudden"... unless you moved from sea level to the high mountains - 8,000ft. or higher!!.. there is an assignable cause for the backfiring and the exhaust getting red hot ..RED HOT IS WAYYYY TOOOOO HOT!!!!! ,,, you have probably already damaged the engine.

Take this thing to a PROFESSIONAL!!!!

Carb is ajusted to lean it needs to be richend the reason for the pipe glowing is its running hot due to the fact the carb is to lean discontinue use or you might burn up the motor!