Run them on white gas/Coleman fuel and never worry about gas going bad ever again! A little more expensive to run, but I've never had to worry about having the carb varnished up. I had to richen my Stihl just a smidge and I mix a little extra oil to make up for a drier gas, but it is worth it!
Details? Never ran white gas, but I run all my stuff on 91 no ethanol, or the canned stuff from Stihl/Echo etc