Just a data point, but the gasoline that's in my tank now is about 2 years old and I just started and ran the generator the other day. It started up easily and ran okay. I rarely use the generator so the tank is never full, which is not a good idea, but I just can't see hauling a full tank of gas when I may use it every two or three trips. Usually about a half-tank or less. I always drain the carb after every use so that may help.
I'm seriously leaning toward changing it over to propane to avoid problems with gasoline. I use it so infrequently that a 30# tank would last me forever, and probably a 20# tank would be all I would need.
As far as the green balls in the filler tube, I also lean towards the anti-spill/slosh devices.
