Backfiring through the intake happens every once in a while to me and I don't think it's attributed to a lean condition. My A/F ratio is 13.5 to 1 and it still happens to me. However exhaust popping on decel or afterfiring is a sign of a lean condition.
DougL did some datalogging a while back and this "recipe" that was created and has worked very well for me and some others in reducing the afterfiring.
http://www.r3owners.net/showthread.php?t=1804
