After studying that plug some more, I would say your tuning/mixture is spot on, but it is in fact time to swap out the plug for a new one. Try .020 - .022 for the plug gap. You may have other problems for the sudden stoppage as discussed though; it's just that I would change the plug anyway. If the plug were the direct cause of the stoppage, I would normally expect much more misfiring before quitting.

AV8TOR