What Causes My Motorcycle to Backfire Thru the Exhaust?

When a motorcycle engine has an emission system malfunction, such as an exhaust leak or a moment of running rich or running lean, backfire occurs as a result. When an engine is running rich, there is more fuel present than air, according to DoItYourself.com. When it is running lean, there is more air than fuel. In either case, the result is an incomplete combustion causing the loud popping noise.