After beating the tar out of my arm last week, I'm thinking that the magneto is suspect. Spark strength has become erratic and the engine doesn't want to stay lit. No change in air gap and you'll notice no kill switch, so it wasn't that either. I've had problems with these weed wacker ignitions on weed wackers. The eBay Tillotson clone is also junk, so this part of the experiment was fun, but over.
There's one thing I have have had excellent results with, and that's the combination of an inductive coil, 12v power, and a microcontroller. Different engine;