Agree with mowermech, not a great chance that adding stuff to the fuel will clean out the gummed up carbs.
What you're seeing is absolutely that condition. Runs better on choke means the fuel circuit is plugged or varnished up from old gas and not providing enough fuel through the jet(s).
If they're not throwaway carbs (is you can actually disassemble them) then disassembly and cleaning the carb is what needs done.
IMO you'd have to run them too long with any additives/carb cleaners to make it worthwhile and you're also putting more wear on the engine doing that compared to it running proper A/F ratios.
Take one apart. They're pretty simple and easy to clean. If they run that bad you'll probably see the problem. Main jet will likely be clogged.
Coming from a pawn shop, they don't GAF so do your diligence and check compression before buying, since you can't test them running properly.
And idk if Yami has a built in hour meter like the hondas but may research that.