Last year, I let a fairly new portable generator with low hours on sit with gas in it for 6 months and it would not fire up. It wouldn't even sputter.

That was surprising to me because it was working quite well when parked, and I'm used to doing things like leaving lawnmowers outside continuously (including over the winter) without much trouble, but that's what happened anyway.

I drained the old fuel out and replaced with fresh, and it fired up on the first subsequent half-assed pull of the starter rope.

(Which reminds me: It's been six months again already. Time to see if it still works.)

I just did this as well. Fired up my moped on 2 year old stabilized gas. Runs fine.