I have been running into this same problem for about 2 months now. It has been in the shop 6 times in that span, and they have cleaned the carburetor (first time) and then adjusted the air intake screw the subsequent times. About a year ago, the spark plug and the air filter were replaced.
The bike will run for about a week or so after the screw is adjusted, then it will either not start at all or it will just die on me once it gets up to full speed. At times, it will also stop running when idling at a stoplight (30 seconds or so).
This is a frustrating problem and any advice I could receive would be very appreciated.