Those of you who have battled your way through this can probably appreciate the photo. What an ordeal. Happy to say that it ended in success. I tried several different methods including left hand drill bits and EZ-outs, but ultimately used a "hammer in" extractor to finally get my stuck mixture screw out of my #4 carb. Fantastically nerve-racking... This guy was really stuck, but the hammer in type extractor proved to be worth the $20 cost for a Chinese made tool. Just wanted to share my success for anyone else mired in this dilemma.