If the fuel in the tank isn't the up to 5% ethanol premium type then I would suspect you will have water in the fuel after that long as well as reduced octane levels.Dont rely on the water separator helping out,mine didn't and I got water in my injectors cost me a fair bit to get it sorted and I dumped the fuel in the tank.This happened on a couple of occasions as I was using the non premium fuel at the fuel berth. I ended up removing the 100 litre stainless steel tank and converting to portable 25 litre plastic tanks that I could fill with Esso premium at my local garage which had Zero Ethanol.
No further issues and fuel was always good enough to start and run even after many months without use.