Store-bought premix is already stable. Homemade premix needs help.

If you bought a branded ethanol-free premix, skip the stabilizer; if you mixed it yourself, add it.

Commercial ethanol-free premixes like TruFuel, VP Racing, and Stihl MotoMix are blended to sit for years. They already contain stabilizers, and there’s nothing in normal storage that will break them down in six months or even two years. Read the label if you want proof — most say something like “up to 5-year shelf life.”

Homemade premix is a different story. Even ethanol-free premium pump gas starts oxidizing after a few months. It doesn’t phase-separate like E10, but it does form gum and varnish that can clog a carburetor. Premium octane doesn’t make it last longer. For your own premix, a fuel stabilizer is cheap insurance, and six months is right around the point where oxidation becomes a real risk.

One shortcut: store it in a full, sealed metal container in a cool place. That slows oxidation more than anything else, but stabilizer still makes it bulletproof.

Stabilizer is the cheapest carburetor insurance you’ll ever buy.