I had something like that happen on my E16 b11, it made me insane for a long time, what i finally discovered was the dizzy had fallen apart inside from vibration, and for some reason it would run 5 min maybe 10 then get odd and die, then after sitting a few minutes, maybe an hour run again, repeat.

try swapping dizzys.

yes it looks like a fuel problem but that's not it ;) which is why it took me so long.