It has been said that temperature cycling will make fuels with castor oil run better. I have part of a jug of fuel that is about 30 years old. I run some of it through an engine on the bench from time to time and it runs fine. I wish some one would run an experiment to see if the problem with open fuel is more water absorption or methanol evaporation. If it is water absorption the fuel sample should gain weight, if methanol loss the fuel would lose weight. Eventually it would lose weight as both water and methanol evaporate, I suppose.