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Burning of a mixture through the induction system in a reciprocating engine. It is the process of extended combustion into the air intake manifold, supercharger, and carburetor or by mechanical faults. The popping sound heard at the moment of switching off the engine is an indication of backfiring. A loud bang from a reciprocating engine is the result of the premature ignition of the fuel-air mixture in the induction system while the intake valve is still open. The flame travels through the inlet valve and along the induction manifold. A lean fuel-air mixture is a common reason for backfiring.