I've seen this happen twice believe it or not. a rag was put in an airbox and missed during assembly. enough air to idle but dies above that. thats my only experience with your symptoms.hope someone has a better answer.
Ross..
My Rides
1985 250R original (Garage Queen)
-under restoration
1985 250R black and blue full rebuild ( Daily Rider)
-Paul Turner pipe
-+2" Westcoast
1985 Red and White Tecat-EH Sold
1985 Green Tecate Sold
My Wife's Ride
-2003 Suzuki LTZ 400 Showroom fresh and completely stock
My Kids Ride
-2004 Yamaha Blaster, Completely Stock
-2006 Yamaha Blaster, Completely Stock