Old Gas in Tank

7 months is not too old for the tank. You most likely just have stale gas and a drain and refill should cure this.

The ethanol/varnish problem usually arises from cars that have sat unused for many years (before ethanol was in the gas) and then refilled with fuel containing ethanol.

Ethanol attracts water, and also separates from fuel after 30 days. After 6 months or a year, you could have a nasty combination of stale gas, and water soaked ethanol in a tank.

Ask anyone with an old boat what happened to their inboard fuel tanks after ethanol was added to gasoline.