I wouldn't say the ethanol is the problem, but perhaps the brand of gasoline. I can tell you that many cars including my own run crappy on certain gasolines (even though all gasoline contains 10% ethanol), when they get older. For example I get horrible gas mileage on Exxon gas, while I get wonderful mileage on Shell or BP gas. Experiment with that a little and if there is no improvement you (or if your not sure how a shop that deals with generators can do it for you) can adjust the idle and check any filters that may be one the generator.
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I wouldn't say the ethanol is the problem, but perhaps the brand of gasoline. I can tell you that many cars including my own run crappy on certain gasolines (even though all gasoline contains 10% ethanol), when they get older. For example I get horrible gas mileage on Exxon gas, while I get wonderful mileage on Shell or BP gas. Experiment with that a little and if there is no improvement you (or if your not sure how a shop that deals with generators can do it for you) can adjust the idle and check any filters that may be one the generator.