i think the key is that both cylinders read the same. anything catastrophic would probably only affect one jug. i guess if the cam chain jumped timing you could see this but it looks like you checked this out ok.
raw gas dumped down its throat could cause the intake backfire in a normal engine. i think spark occurs on the exhaust stroke as well and there is probably valve timing overlap so raw gas sitting there is going to go poof back through the intake
I would keep hunting for a fuel problem but if you have the opportunity, test your compression gauge on a known good running cylinder
sorry if i sounded annoyed, i was merely confused