Probably not the issue here but I've had problems with a new Magnum XLS 46 the last 2 times I went flying. It was still in break in stage so running rich, became very hard to start (I no longer have an electric starter, if it won't start by hand, I don't want it), ran great for about 5 minutes in the air at full throttle then seemed to go VERY lean and unless I cut power would die. I never had a Magnum before and was about to swear to not have this one very long. I've been in the hobby since 1972 and there have been very few 2 stroke engines I couldn't tune. This was back when Fox was most popular, then probably Enya, and if you were in the "elite" group of pattern fliers you probably had a Super Tiger with a tuned pipe. But I digress, when I was just about mad enough to turn the engine into little pieces, I was in the process of refueling and trying to "tweek" it again, and found the muffler to be slightly loose so I tightened it up of course, guess what, it ran like a charm!!! Of course the adjustments I had been making had put it on the super rich side but easy to correct. before the day was over (yesterday) it was starting and running like a dream and again starts with one or two flips. Guess I'll keep it now ;-)
Dan