mansvoice..
Morgan fuel has only 17% oil so switching to the Sig with 24% oil definitley means a retune is needed. I'm guessing he didn't retune so it ran leaner causing the dead stick. Any time you change fuels, even if the labels say they're the same blend, you should retune.

That Sig "2 stroke" fuel should be fine in a 4 stroke. One thing that should always be remembered is that too much oil has never killed an engine .