how long for fuel to go "bad"?

[philipp10]

It all depends upon the container and how well it is sealed. High temperatures factor in as the volatile components will evaporate, but only if the container leaks. Another issue is temperature swings, they drive the internal tank pressures up and down, potentially pulling air in when its cold and driving it out in the heat. But again, not if the tank is sealed. Like I said, this old jetski sat out in Minnesota for 5 years. We have very cold winters but also very hot and humid summers. The gas was just fine. 5 years!!!

 

[Nyogtha]

The main issue is not letting the olefins in gasoline polymerize or oligimerize into chains long enough to create higher levels of gums in the gasoline than when it was produced. Increasing temperature also helps drive this reaction.

Gasoline blending streams containing olefins are typically dosed with a gum formation inhibitor (or antioxidant) before they're routed to storage / tankage, as exposure to oxygen increases the potential for gum formation. For prolonged storage, it helps to have an extra dose of such chemicals. This is especially true if the container 'breathes' with changes in temperature as phillip10 has noted, as this renews the oxygen content of the vapors in contact with the liquid each time it 'breathes' in.

Jet fuels typically get a dose of antioxidant when produced as well. A good thing there too.

 

[Tundragod]

I have a 1 gal fuel mixed for my 2-cycle Poulan weed wacker since 2005. Fuel is still working in the Poulan but it ate all the fuel lines because I never winterize or dump the fuel out. I replaced the fuel lines. I barely use the wacker hence, I still have the fuel. Fuel looks black. It takes forever to start the wacker now......Probably needs new fuel mixture.

 

[Nyogtha]

It has likely lost all the lower-boiling components in the gasoline blend that readily vaporize allowing some vapors in the carb intake at this point. You can overcome this with some spray starting fluid if you're set on continuing to use it - obviously it runs once you get it started or you would have mentioned that.

I don't think black is a hip color for gasoline though. In all my years of dealing with it that's a shade I've never seen.

After 9 years of this diet I agree you should reward the weedwacker with some new, improved 2 cycle mix.