Chevron and all other gas stations all use the same gasoline. This is because no gas vendor uses a private pipeline system. Basically the only differences between vendors are the chemicals added to the gas by the companies at the stations. These additives are designed to do anything from cleaning fuel injectors to preventing carbon buildup. They do little to nothing for complicated modern engines and they surely would not effect a little two stroke.
Personally I buy the cheapest gas I find, but if it makes you feel better paying a little extra for name brand, at around 150mpg I don't think its gonna break the bank.