Most generators spend far more time in storage than running, and most of the ones that fail to start on the day of an outage failed because of how they were put away. The culprit is nearly always gasoline that went stale in the carburetor. Ten minutes of preparation prevents it.
Quick answer
For storage of a month or more, either add fuel stabilizer to a nearly full tank and run the engine for several minutes so treated fuel reaches the carburetor, or drain the tank and run the carburetor dry. Change the oil if it is due, clean the generator, disconnect or maintain the battery, and keep it covered in a dry, ventilated place away from living areas and anything with a pilot light.
In this guide
Why stored generators fail
Modern gasoline, especially with ethanol, starts to degrade within weeks. Lighter components evaporate, leaving gum and varnish that block the tiny passages in a carburetor. Ethanol also attracts moisture, and in a vented tank the fuel can separate into a layer of water and alcohol that will not burn. The result is an engine that cranks but will not fire, or runs only on choke. Our article on how long gasoline lasts goes into the chemistry.
Short-term storage: up to about 30 days
- Top up the tank with fresh fuel and add stabilizer at the dose on the bottle.
- Run the generator for five to ten minutes so treated fuel is in the carburetor.
- Close the fuel valve if the generator has one.
- Check the oil level, wipe the unit down and cover it.
Long-term storage: more than a month
You have two good options. Either works; pick the one that suits how you use the generator.
Option A: Stabilize the fuel
- Fill the tank to about 95 percent with fresh gasoline. A full tank leaves less room for moist air to condense.
- Add fuel stabilizer at the storage dose.
- Run the generator under a light load for 10 minutes to circulate the treated fuel.
- Shut the fuel valve and let the engine run until it stops, which empties the carburetor bowl. Not every manual recommends this; check yours.
Stabilized fuel is commonly good for 12 months, and some products claim longer. Write the date on a tag.
Option B: Drain the fuel system
- Run the generator until the tank is nearly empty, then siphon or drain the rest into an approved container.
- Shut the fuel valve and run the engine until it stalls from lack of fuel.
- Open the carburetor bowl drain screw, if fitted, to let out the last of the fuel.
A dry carburetor cannot gum up. The disadvantage is that you need fresh fuel on hand when the outage comes.
Engine and electrical care before storage
- Change the oil if it is near its interval. Used oil contains acids and moisture that attack bearings while the engine sits.
- Protect the cylinder on long storage: some manuals suggest removing the spark plug, adding a teaspoon of engine oil, turning the engine over gently with the starter cord, then refitting the plug and pulling the cord slowly until you feel resistance, which closes the valves.
- Battery. On electric-start models, either disconnect the battery or keep it on a maintenance charger. A flat battery in storage is often ruined.
- Clean the generator. Dust, grass and oil residue hold moisture. Clean the cooling fins and air intake.
- Check the air filter and spark plug so they are ready for the next start.
Where to store it
- A dry, ventilated place such as a garage, shed or covered area, on a level surface.
- Away from any appliance with a flame or pilot light, and away from living areas, because fuel vapor can escape from the tank vent.
- Under a breathable cover rather than a plastic sheet, which traps condensation.
- Somewhere you can wheel it out easily in the dark, with the cords, funnel and fuel nearby.
- Out of reach of rodents, which chew wiring and nest in air filter housings. Check the recoil housing and air box when you bring it out.
Exercise it while it waits
If you can, start the generator every month or two and run it under some load for 20 to 30 minutes. It keeps the fuel system wet with fresh fuel, charges the battery, lubricates seals and tells you about problems while the lights are still on. If you cannot exercise it, Option B above (a dry fuel system) is the safer storage choice.
Bringing it out of storage
- Check the oil level and top up if needed.
- Check for rodent damage, cracked hoses and loose connections.
- Fill with fresh fuel, or open the fuel valve if the tank was stabilized.
- Reconnect or charge the battery.
- Start the generator outdoors, let it warm up, then test the outlets with a lamp or a drill.
- If it will not start, work through our generator will not start checklist.
Frequently asked questions
How long can gas sit in a generator?
Untreated gasoline can cause starting trouble within a month or two in a vented tank. With stabilizer added to fresh fuel, most products claim 12 months or more. If the fuel is older than that, drain it and start fresh.
Is it better to store a generator full or empty?
Either is fine if done properly. A full, stabilized tank limits condensation and means the generator is ready to go. An empty tank and dry carburetor cannot gum up but needs fresh fuel when you want to run it. Half-full with untreated fuel is the worst option.
Can I store a generator in the house?
It is not recommended. Fuel vapor from the tank vent can build up indoors, and any spilled fuel is a fire risk. Keep it in a garage, shed or covered outdoor area, and never run it there.
