VZ800 ran rich, now lean under acceleration

A few weeks ago, I got the bike out for the first spring ride for a couple hours. The engine ran rich, and after highway runs, I had to babysit the throttle to keep it from stalling. I parked it in the garage and made no adjustments.
Last weekend, I tried to run it up the street, expecting the same situation. When I accelerated, it pulled hard, but then immediately fell on its face. After some investigating, I found a lean condition now. I pulled both carbs, checked for debris, and cleaned them thoroughly, checked float levels, and reassembled the bike. When I started and revved the engine, it ran strong then rpm dropped and lots of backfiring from the exhaust. Several times today, I did this same process, thinking there's something I missed. I found nothing amiss with either carburetor. If I cover the main air jets with my fingers, it seems to perform properly. I even swapped a spare rear carb, and got the same results. I'm about to lose my mind...
Does anybody have an idea of what to do now?

Have you put fresh gas in?

Yes.

I posted my situation on another site. As it turns out, my folly was running with the carbs open. It was explained to me, that the filter boxes act somewhat as restrictors, and the engine shouldn't even run without them. That explains why it wouldn't do much more than idle. Once I put the filters back together and synchronized the carbs, it ran great!

Glad you got your answer :) 
Lots of members on here have fuel injected bikes, so may not have known the answer...