Been doing a LOT of reading of the FAQ and the forum (and some googling) and I haven't run into a solution just yet. If this question's been answered, feel free to point me in the right direction to find the post.
I recently purchased an '01 Ninja 250 that was not running. The bike looked in pretty good shape.
I pulled out the carbs, cleaned them thoroughly with cleaner and a small copper wire, measured and adjusted the floats, put the idle mixture screws at 2.5 turns, reinstalled the carbs, and then used a jumper battery to get it started (bike battery was dead).
The bike starts strong, but idles around 3000 rpm, and then (after about 3-5 minutes of running) starts to die unless I open the throttle.
I thought I had adjusted the floats wrong, so I pulled the carbs again, re-measured (everything looked good), and cleaned a few jets again just to be sure. I reinstalled the carbs, and this time it wouldn't start and had gas coming out the carb overflow tube. I figured some debris had gotten under one of the float needles, so I pulled the carbs one last time, and cleaned again.
Now the bike is doing the same thing as I mentioned earlier. Starts, idles at 3k for a few minutes, and then dies.