Holley Carb help

One other thing to check is that when it back fired that it may have bent the throttle blades a touch and this will make it rpm higher, depending on what rpm's the engine was turning at the time of backfire. We have had them backfire and blow out the small teflon seals out of the throttle shafts and create a vacuum leak, makes it hard to find but with some carb spray will definitely show where.