Hey Rez,
I had the same exact problem with my daughters raptor 80, And so did my Brother-in-law with my Niece's raptor 80!!!
Mine happened last year, 3 weeks after the warrenty expired. I took it to the Yamaha dealership and the mechanic told me that it was the 4th one he had seen with the same issue. He added that the carburator was designed with a flaw.
Needless to say I had to contact Yamaha directly to see if they would at least meet me half way with the repairs. They picked up the labor charges which I was pretty happy with, since I only had to pay for the bent valves and a piston. approx $150.
My Brother-in-law had the same issue last month! Although when he saw what had happened with mine, he purchased the extended warranty for $99.00. Cheap insurance since his bill was almost $1000.00.
First thing I did when I picked it up was pull out the carb and locktite the screws!!!