I'm no expert but does anyone think a screw has vibrated loose? Like the one holding the carb to the case or any of the backplate screws?
It may very well turn out you are completely correct but these types of problems don't usually lead to the problems described. A loose backplate screw and carb screw usually result in a lean condition at higher speed. Abruptly quitting at idle (or near idle) is usually bad fuel. Quitting when you remove the igniter is usually a bad plug.
Bill