RE: Glow plugs... need some suggestions
Are you running a bladder tank? If not isolate the tank on foam rubber. You could be foaming. Don't let it run out of fuel, shut it down. I you were using a fuel cut off, that would be sudden, but you are getting a lean run for a bit before it dies. Try the K&B HP plug, my OS DF engines are getting at least 25 flights on 30% before I replace it due to the performance drop (the wire looks dull & frosted).
Food for thought, my 8oz. tank last only 3 minutes, you are getting 6 or 7? True you are useing 15% but thats still a lot of run time. Too lean???