A generator that won’t start after months in storage is one of the most common (and most frustrating) issues homeowners face — usually right when a storm is already rolling in. The good news: it’s almost always one of four fixable issues, not a dead unit.
1. Check the Fuel First
Gasoline degrades within 30-60 days without a stabilizer, forming varnish-like deposits that clog the carburetor and fuel lines. If your generator sat all summer with old gas in the tank, this is the most likely cause.
Fix: Drain the old fuel completely, and refill with fresh gasoline. If the carburetor is already gummed up, it may need cleaning or replacement.
2. Check the Spark Plug
A fouled or worn spark plug is a fast, cheap thing to rule out. Remove it and check for heavy carbon buildup, wear, or a wet plug (indicating flooding).
Fix: Clean a lightly fouled plug with a wire brush, or replace it outright — spark plugs are inexpensive and it’s good practice to swap them each season regardless.
3. Check the Battery (Electric-Start Models)
Electric-start generators rely on a small battery that can fully discharge during months of storage, especially in cold conditions.
Fix: Charge or jump the battery, or use the manual pull-start backup if your model has one, then plan to trickle-charge the battery during future storage periods.
4. Check the Air Filter
A severely clogged air filter can prevent proper air-fuel mixture, making starting difficult or impossible.
Fix: Clean or replace a dirty foam or paper air filter — this is typically a tool-free, 2-minute fix.
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For preventing this exact problem next season, adding fuel stabilizer (such as STA-BIL) to the tank before storage keeps gasoline from degrading and gumming up the carburetor — a few dollars spent now saves an emergency repair later.
If the spark plug is the culprit, a basic NGK or Champion replacement spark plug matched to your generator’s specific model is inexpensive and should be part of routine seasonal maintenance regardless of whether it’s currently causing problems.
For electric-start models with a battery that won’t hold a charge after storage, a compact trickle charger/battery maintainer keeps the battery topped off during months of non-use, preventing this exact issue from recurring.
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Quick Diagnostic Table
| Symptom | Likely Cause | Fix |
|---|---|---|
| Starts briefly, then dies | Gummed carburetor from old fuel | Drain and replace fuel, clean/replace carburetor |
| No spark, won’t start at all | Fouled/worn spark plug | Clean or replace spark plug |
| Electric start does nothing | Dead battery | Charge, jump, or use manual pull-start |
| Hard to start, runs rough | Clogged air filter | Clean or replace air filter |
Common Mistakes to Avoid
Leaving old fuel in the tank between uses. This is the single most common cause of a no-start generator — always drain fuel or use a stabilizer before storing for more than a month.
Skipping annual spark plug replacement. It’s cheap and prevents an entirely avoidable no-start situation.
Not running the generator periodically during storage. Manufacturers commonly recommend starting and running a generator for a short period every 1-3 months to keep components lubricated and fuel fresh.
Assuming a no-start means the whole unit is dead. Most no-start issues trace back to fuel, spark plug, battery, or air filter — not a major internal failure.
FAQ
Why won’t my generator start after sitting all summer?
The most common cause is degraded fuel gumming up the carburetor, followed by a fouled spark plug, dead battery (electric-start models), or clogged air filter.
How do I prevent this from happening again?
Use a fuel stabilizer before storage, or fully drain the tank. Run the generator briefly every 1-3 months, and keep the battery on a trickle charger if it’s an electric-start model.
Should I replace or clean a gummed-up carburetor?
A lightly gummed carburetor can sometimes be cleaned with carburetor cleaner, but a heavily varnished one is often easier and more reliable to replace outright.
How often should I change my generator’s spark plug?
Most manufacturers recommend annual replacement, or roughly every 100 hours of use, whichever comes first.
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