Ken, You may want to 'start' your "non-starter" investigation by going back to the last thing you did... adding the Stabil to the fuel. Was the additive well mixed with the gasoline before opening the petcock and start up or just poured in?
So, pull the float bowls and check for fuel, debris, or perhaps the Stabil went right through the petcock and into the carbs.
Hall sensors can have temperature issues but it's usually heat induced. After cooling, they're working again. Doubt that's your issue but checking for spark is an easy job.
Also, high idle rpm after a lengthy ride can be the occasional sticky advance weights or an idle air mixture issue. I'd go with a tweak of the mixture screws when the engine is well warmed.
Go back to the shed and find out why it's not starting for you. It will be something of an "Ah, Ha" deal.