Got Shell 93 Octane and now barely idles 1973 Dart 340

Maybe your American gas ages different than our junk.lol But we haven't had 93 non-oxygenated around here since 99 or so.
Hey I just thought of something; maybe the color-change in 93 differs from the color-change in E10.Maybe that 93 doesn't lose it's potency with color change. Are you using that 93 in a newer weed-whacker by any chance; one with a non-adjustable carb? I wonder how it performs...........

Maybe one can't depend on color-change in stabilized 93, to be a potency indicator