Troubleshooting - idling

So I've been working on reviving a friend's bike that hasn't been used for 10-15+ years. I pulled the carbs and cleaned all the jets in my ultrasonic cleaner, and I blew compressed air through allthe passages in the carbs. Got the carbs mounted back on the bike, engaged the choke, and fired it up. It started up and warmed up to about 4krpm. I turned the choke off slowly and the rpms dropped to 1k. Giving it any throttle with the choke off kills the motor. If I leave the choke on and let the bike idle at a high rpm, the throttle response is great and it doesn't bog the bike down.

Also, after warm up, when idling at 1krpm for maybe a couple minutes, the motor sputters out and dies, and I can't seem to get it to start back up.

Any ideas what's going on with this bike?

 

where is the fuel float level?
where did you set the mixture screws?
did you do a running sync?

 

I didn't touch the fuel float level from when the bike was last running. I did check the mixture screws, it looks like they were set to 3-1/4 turns out. I did try putting them at 2-1/4 turns out, but the motor died out with that, so I returned them to 3-1/4 turns out. Running synch not done yet, due to time constraints. Can the running synch be done at 3 or 4krpm?