keep running gas treatment till you can do something with carbs, you might be surprised byit clearing up on its own,snyc pluged carbs dose nothing, usely you can take the plugs out and see the difference in plugs to see which carbs are having problems,gas treatment to me is two cycle oil or atf it dosnt have to be hi dollar stuff, sometimes the carbs are fine and its all ignition stuff bad wires, ends , ballist resister,coils or fouled plugs from being drowned by bad carbs.
in your case it sounds like you have both deals going on with that kind of gas mileage .so your at the bottom end of running right now. so if i were you id be broad minded and go for improvement in all the areas . the tank needes to be clean or at least drained and flushed
you dont need to spend a lot of money at frist just check plugs only when cold ,rotate plugs get a feel of whats going on ,keep treating the gas with somthing and ibet things will get better and you will learn what going on though observation and get to know your wing
whenever you get things worked out dialed in from where your at the difference will be like a new bike