With the Ethanol in American gas these days (Thank you EPA!!) I prefer it never sit more than a week, especially in my carb. If my riding lawnmower sits for more than a few weeks (winter) with fuel in the system it completely gums the fuel pump and I have to let it soak in carb cleaner. Same go's for the fuel lines. I had to replace every inch of fuel line on it late last year because it quit running one day. Pulled the tank off and the inner liner of the fuel line had melted and basically turned into a thick black melted rubber/tar substance shutting off the fuel supply. I need to buy stock in Sta-Bil as it's now added to every fuel can I own to minimize the damage of Ethanol.