I've used the NorVel tankmount on a couple of trainers and it works flawlessly, but delivers very short runs. These things are very thirsty, but all that power requires fuel. It's actually a pretty good idea on trainers, as if you aren't using really long lines, a novice will be spindizzy in short order!
If the check valve on the tankmount isn't sealing properly (maybe a teensy bit of crud?), it might cause just this problem. Engine starts, runs, and launches OK, but as soon as it tries to lean out in a maneuver, suddenly the fuel flow just isn't sufficient, and it dies. My best guess . . . .