Just listened/watched the latest video you posted. It is definitely rich on the low end. The high speed miss is questionable. I would still try a new ignition. If it runs fine on the ground from idle to half throttle, but goes rich in the air, then it is pressurized air in the cowl as described by Adrian. You can plug that Stihl rectangular regulator cover vent with something like epoxy, (I use Seal All), then drill and tap it for a fitting and run a vent line into the fuselage. I do this on all my planes.
If you can't get it to run lean enough to not four stroke while flying at low to mid range power, but still give good throttle response, then try a larger prop. It sounds like your prop unloads quite a bite even in a mild dive, which makes me think you have plenty, if not too much pitch. Try going with a larger diameter. It will load the engine harder, possibly help with leaning the low end/mid range out, and give you a thrust boost as well.
AV8TOR
Last edited by av8tor1977; 09-24-2016 at 02:01 PM.