What are the manifestations of engine backfire?

[AndresFitz]

Engine backfire manifests as: 1. The burned mixture escapes through the intake valve into the intake manifold and ignites some fresh mixture, accompanied by "pop" noises; 2. Decreased engine power and jerking during acceleration. Common causes of engine backfire can be divided into two categories: excessively lean mixture and abnormal ignition timing. Normal engine operation consists of four steps: intake, compression, power stroke, and exhaust. Backfire occurs when, after the piston completes the power stroke, the exhaust gases that should be expelled through the exhaust pipe cannot be discharged due to certain faults, such as the exhaust valve being closed or unable to expel the gases in time.