Hi Stormilm, good to see some activity in the forum again. ;)
Flameout may occur if you fly inverted. I quote the Flight Manual:
Flying inverted or with negative G:s is restricted to max 15 seconds to prevent fuel flow problems. The buffer fuel tanks aid in keeping the fuel flow uninterrupted, but after prolonged inverted flight you may experience flameout.
The model regards bank angles exceeding 100 degrees as inverted flight, so this may be the cause of your problems. You should be able to fly inverted for a while before the buffer tanks are dry though. If you flameout immediately, maybe the buffers are already empty. Check the fuel levels in FSX, the buffers are Center 3.