Generator Won’t Start After Sitting All Year? The 30-Minute Carb Fix
Most often, a generator that won’t start after months in storage has one problem: stale fuel gumming up the carburetor. Here’s the fix, in the order that actually works.
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Before you assume something’s seriously wrong, know this: a small engine that sat for more than 30 days with gas still in the tank is the single most common reason generators won’t start, and it’s almost always fixable in under an hour with tools you probably already own. Work through these steps in order — many no-starts are solved by fresh fuel or a carb cleaning.
| What You'll Need | Notes |
|---|---|
| Fresh gasoline | 1 gallon, non-ethanol or E10 max |
| Carburetor cleaner spray | 1 can |
| Fuel stabilizer | For next time — prevents the problem entirely |
| New spark plug | Cheap insurance if the old one looks fouled |
| Basic wrench/screwdriver set | To access the carb bowl on most models |
Step 1: Check the Obvious Stuff First
Confirm the fuel valve is open, the choke is set correctly for a cold start, and the on/off switch is actually in the “on” position. It sounds too simple, but a surprising number of “broken” generators are fixed by this step alone.
Step 2: Drain the Old Fuel
Gasoline starts breaking down in as little as 30 days, and ethanol-blended fuel absorbs moisture over time, both of which gum up the tiny jets inside the carburetor. Drain the tank and carburetor bowl into an approved gas can (take old fuel to a hazardous-waste drop-off), then refill with fresh gas. This alone resolves a large share of no-start cases.
Step 3: Clean the Carburetor
If fresh fuel doesn’t do it, the jets themselves are likely clogged with dried-out fuel residue (varnish). Most small engines have a drain screw or a removable bowl at the bottom of the carburetor:
- Locate the carburetor bowl (usually a small brass or aluminum cup below the air filter).
- Remove the bowl and spray carburetor cleaner directly into the jets and the bowl itself.
- If spray cleaner doesn’t clear the jets, don’t force anything through them; a carburetor rebuild kit or a small-engine shop is the safer next step.
- Reassemble, refill with fresh fuel, and attempt to start, outdoors, at least 20 feet from the house.
Step 4: Check the Spark Plug
Pull the spark plug and look at the tip. A plug that’s black, wet, or crusted with deposits won’t fire reliably. Spark plugs are inexpensive enough that replacing one preventively whenever you’re already this deep into troubleshooting is worth doing.
Pros
- If it starts now: run it outdoors, away from the house, for 10–15 minutes to burn off any remaining residue before storing it again
- Add fuel stabilizer to the tank before your next storage period to prevent this from happening again
Cons
- If it still won't start after all four steps, the problem is likely deeper (fuel pump, ignition coil, or compression) and worth a small-engine shop visit
- Don't keep cranking an engine that smells of gas; you can flood it further and wear down the battery or starter. Let it sit a few minutes first
Check Carburetor Cleaner Small Engine on Amazon → Check Fuel Stabilizer on Amazon →
Prevent This Next Time
The fix for next season is simple: add fuel stabilizer to a full tank before your last run of the season, run the engine for 5–10 minutes so the stabilized fuel reaches the carburetor, then store it with that treated fuel still in the tank rather than draining it completely. Most stabilizer products keep fuel usable for 12–24 months.
FAQ
Read next: What Size Generator Runs a Fridge AND Freezer · Can You Run a Generator in the Rain
Sources
- Briggs & Stratton: fuel stabilizer: fuel degrades in as little as 30 days; store with treated fuel
- Generac: cleaning a portable generator carburetor: carb cleaning steps
- CPSC carbon monoxide safety tips (2025): run outdoors, 20 feet away
Checked September 2026. Prices and specs change; confirm on the linked pages before you buy.
