It sounds like you may be running too lean. Here's what I read on another forum:
1. You can't run it without the airbox lid on. Its way too lean
2. If it's still lean, check for water in the bowls, Cracked boots, tight valves or weak fuel pump.
3. If all that checks out, try running it with the tank cap loose. If its good, replace the vent check valve.
4. Check your fuel pump