I have not changed a thing on my m500, but all of a sudden the fuel tanks are becoming pressurized. I put new gas caps on, but it did not help. It will actually spew gas out from the gas caps.
those machines are to use two vented gas caps if I remember right , you might get away with one vented and the other non-vented to keep evaporization down but as the weather heats up this pressure will become moreso unless vented.