mmmm, from experience with other bikes, the issues your describing sounds like it's starving for either gas, or air. If you're able to describe the sound a little better, or maybe take a video, I might be able to know which one....
You might want to check:
1.) fuel filter for being clogged
2.) fuel line pinched
3.) vacuum line pinched
4.) air box - rubber boots and such for a possible blockage (although doubtful)
5.) Maybe even a leaf blocking the snorkel (more probably)
But as Felix said, when diagnosing an issue, start with the basics, and as you eliminate variables it becomes that much easier to find the problem...
