So here's the deal. I added a drop-in K&N filter, rejetted my carb (20/60/137.5), and swapped out a couple valve shims to bring everything into spec. After putting it all back together, I can't get it to start up.

when i first tried to start it up, I had the air/fuel screws at their stock setting. After no luck getting it started, i turned them all the way in. I still couldn't get the bike to turn over. I then tried partially covering the air intake with my hand, and got it to turn over. It ran (but rev'd high) until I took my hand away.

I take this as i am way lean. Which surprised me. I thought that the rejetting would have more than compensated for the air filter. I tried turning the air fuel screws one full turn out, and tried to start it again. No luck.

I haven't been able to get it to fire again. Even when i was trying to replicate the first (with the air/fuel screws all the way in), nothing. I have a strong spark, air is being pulled through the air filter, and there's gas in the carb bowls.

Any idea what i did messed up?

I likely won't be able to try it again tonight since i killed my battery this afternoon. It's currently on a charger...

After looking around the site, I'm having the this exact problem. Exact sound when it's running

http://gstwins.com/gsboard/index.php?topic=66695.0

The mixture screws should never be fully seated as that results in no fuel to the pilot circuit; min is ~1.5 turns out.

Also, the idle adjust knob should be set such that the butterflies can never fully close (always slightly ajar).

With the stock pipe and K&N drop-in (no restrictor ring) I was jetted to 20/60/142.5 with 2.5-2.75 turns out; she was running superbly.

Ok so i tried several different turns out. First i tried 1 turn, then 1.5. Both with no luck starting. Then i tired 2 turns; after holding my hand over the intake for a second or two, i moved my hand to cover half, and it fired. I was able to keep it running for a min or so, but i had to keep the intake partially covered and it ran really rough (like the video in the thread i linked above). I then tried 2.5, and 3 turns but couldn't get it started at all. I went back to 2 turns, and couldn't get it started again.

I have no idea what's going on... Any other thoughts?

How about the idle adjust knob (aka throttle stop)?  Have you tried turning that in any?

Ok so quick update. I had the vent line from the top of the carbs attached to the drain line on the bottom of the gas tank. I guess i had a flash back to my old bike that needed a vacuum line on the tank petcock... boy do i feel dumb.

After remedying that situation, i was able to get it started in the fashion i described above; 2 turns out, some coverage on the air intake. I'll need to do some more tweaking to get the idle, air/fuel screws adjusted properly since I once again killed my battery trying to get it going.

I hope that this was the only problem. I'll update after i get it running steady...

Ok so another update.

Once again, can't get it started. The swapped hose apparently was not the issue. I'd really like some input on what the problem might be. I have a strong spark, can feel air being pulled through the intake, gas in the bowls, and i can smell gas vapour at the exhaust. I've tried all manner of fuel/air screw positions together with combinations of throttle and choke.

I would think it would still start if the air/fuel mixture was off. I can't figure out why it's not firing.

If no one has any ideas on what could be wrong, I'll be pulling the carb and rechecking valves.

Atomized fuel (at practically any mix), adequate compression and spark at the right time will fire just about anything. You're getting fuel and spark. All that's left is compression and the timing of the spark. I'd have a look in that direction. Good luck!