The two main reasons for stalling a K7 or later 650 are:
1. The TPS is worn so the CPU doesn't "know" where the throttle is positioned and can't supply the proper amount of fuel.
2. The clutch lever switch is bypassed and the wrong information about the position of the clutch lever is fed to the CPU.
If you can start the engine with the clutch lever out, #2 is the problem. Otherwise, you likely need to replace the TPS.