Have you checked to see if the bike has spark after it dies when running for a few minutes? If you have a bad stator sometimes they put out enough to start the bike but as soon as it warms the stator coil stops working.
This happened on a brand new 125 pit bike we bought last year which is how I learned about this. New stator and the bike has run perfectly since that time.
I had to rejet for our altitude but that was expected and normal.
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