"Identifying the Source of Engine Popping Noises in General Aviation"
An expert on engines suggests that a popping sound from the exhaust when reducing the throttle quickly may be caused by a lean fuel mixture. The idle mixture setting should be checked at idle, and if little or no rise is noted, the maintenance facility should adjust the little star wheel on the side of the fuel injector body a couple of clicks towards the rich side. Slowly reducing the throttle allows the system to accommodate the change in the mixture better.