***Definition*** :: An extremely lean mixture either does not burn at all or burns so slowly that combustion is not complete at the end of the exhaust stroke. The flame lingers in the cylinder and then ignites the contents in the intake manifold or the induction system when the intake valve opens. This causes an explosion known as backfiring, which can damage the [[carburetor]] and other parts of the induction system. ***Source*** :: [[AMT Powerplant Handbook]] #glossary