While I was out on the rounds this morning I got to thinking... how are you filling the tank after it's all assembled? As in, through the fill port on the bottom? Holding at an angle? How much liquid are you putting in there? I'm wondering if you're getting a slight vacuum inside the tank which is necessary for it to work. If you cover the air hole, take a few deep draws w/o firing it & then draw with the air hole uncovered, does it gurgle slightly (like it's starting to flood)? Just a thought. It shouldn't be too hard to get this working, so I'm wondering if we're overlooking something simpler.