all motors need FRESH fuel
HOW long fuel lasts depends on many things, , first starting with what type of fuel is it?
ethanol or NON ethanol?
NON ethanol last longer in its basic form?
BOTH can last longer if its treated.
general rule of thumb I go by, is if its NON ethanol fuel, I give it 6 months before it can be IFFY or on its way out(fuel looses Octane as time goes by too)
ethanol fuel, can go BAD in weeks or less! Its JUNK if you ask me., ANY thing I have that sits often, I never use ethanol fuel in it, or NOT unless I treat it first!
Also, keep in mind JUST cause YOU have it say 3 weeks, DOESN"T mean its ONLY 3 weeks old, as you NEVER know how long it sat in tank at fuel station??
simple rule to maybe to go by, if your questioning it, REPLACE IT!, old fuel makes for running or NOT running problems,
drain tank, clean carb, and go new fuel!,
better safe than sorry no?