I can tell you what works for me with my 4 Honda EU generators for many years. I use Stabil marine (blue stuff) with mid octane ethanol laced gas and do not leave any treated gas in the tank for more than a month. When I am through with the generator I siphon all the gas I can from the tank and drain the carb. Then I keep cranking it until it will no longer even try to start. Prior to this procedure I left Stabil treated gas in an EU 1000 for a year and it would not run without the choke on until I had the carb cleaned.
I treat my lawn mower a little differently since it is used more frequently. I use the same blue Stabil but at the end of the mowing season (which for me is in December since I am mulching leaves) I fill the tank and it sits unused until March. I have never had any problem starting my mower. I get rid of the gas purchased in the fall and stored over winter by putting it in one of my vehicle's gas tank and buy fresh mid octane gas to continue the spring mowing.
