it all depends on how it was stored, I've had fuel in my dark cool basement for 3 years and it was good, I've had fuel for less than a month that went bad because the cap didn't seal properly, id say if it was sealed right and was stored in a cool place out of the sun/heat it could be good for awhile. id get fresh fuel and use the old fuel, if it doesn't run or its hard to tune, or rig seems to be running rich and you lean it out and it dies then its bad fuel