the mandated ethanol (corn subsidy) is a big part of the problem with modern gas. it chokes engines and corrodes them. i learned recently that adding a little 2 stroke marine oil with an additive called tcw-3 cleans up the ethanol mess on pistons and rings. really helps an old engine run by breaking up up deposits and cleaning the pistons and rings. i ounce of oil per every five gallons of gas.
i also noticed at the hardware store recently that they sell pure gas (no ethanol) in cans in the lawnmower sections, for the weed-eaters... same issue, ethanol gas kills motors.