Distributor or timing device sticking

Ignition in an internal combustion engine requires specific timing for optimum power. If the timing is off, it will reduce engine power. A spark plug that fires too early will hit the piston on its upward stroke. This can cause knocking. On the other hand, if the spark plug fires too late, the power will hit the piston after it has started its decent. Depending on the type of ignition system, a timing device that is not optimal can cause stalling, backfiring, and a reduction in fuel efficiency. If the timing is only slightly off, the engine may backfire while starting, but run fine afterward. See four stroke power cycle.