Probably multiple fueling issues:
runs only for minute - petrol flow issue through petcock. Can't supply quickly enough to keep float-bowls filled up
dies when throttle opened - is clogged pilot circuit. Need to do full restoration job on carbs, complete disassembly and scrub w/ultrasonic soak. Not quicky spritz with spray carb-cleaner which no longer works anyway.
Check out this thread for photos and procedures:
https://www.ninjette.org/forums/showthread.php?t=375975