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When the lights go out at dinner time and the generator on the porch coughs, sputters and dies, gas generator repair starts with the fuel, the spark and the air. A fault in any of those paths can stop the engine starting or leave it running rough, and the sections below walk through the usual faults in order.
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The quick answer
A generator that will not start usually has stale fuel, a fouled spark plug, a clogged air filter or a gummed carburetor. A generator that starts and then stalls often has the same causes plus a blocked fuel flow. Work through the fuel, spark plug, air filter and carburetor in that order, and check the oil level before cranking again, since a low-oil shutoff can stop the engine. Run a generator outdoors only, far from doors and windows, because of carbon monoxide, and let the engine cool before refueling.
Gas Generator Repair: Common Problems and Fixes
Match the symptom to the likely cause before pulling anything apart.
| Symptom | Likely cause | Where to look |
|---|---|---|
| Will not start at all | Stale fuel or no spark | Fuel tank, fuel valve, spark plug |
| Starts, then stalls | Blocked fuel flow or dirty air filter | Fuel line, fuel filter, air filter |
| Runs rough or surges | Gummed carburetor or stale fuel | Carburetor, fuel tank |
| Runs but makes no power | Tripped breaker or loose connection | Generator outlets, generator breaker |
Start with the fuel
Fuel goes stale in storage, and stale fuel is the most common reason a generator that sat idle will not start. If the fuel smells sour or varnish-like, drain the tank and the carburetor bowl, then refill with fresh fuel. See how to remove gas from a generator for the drain steps.
Check that the fuel valve is open and fuel flows freely to the carburetor. A kinked line or a clogged filter starves the engine even with a full tank, so swap a dark or blocked filter for a clean filter. Use the grade of gasoline your manual names; see what type of gasoline a generator takes for guidance on grades.
Check the spark plug
A spark plug fouled with carbon or wet with fuel cannot light the mixture, so pull the plug and look at the tip. A clean plug has a light tan or gray deposit on the electrode, a black sooty tip points to a rich mixture or old fuel, and a wet tip points to flooding from repeated cranking with the choke closed. Clean a lightly fouled plug with a wire brush, or fit a fresh plug of the type your manual names. See generator spark plug size for help finding the right plug. The plug wire should sit firmly on the plug, and the plug should be snug, not loose.
Check the air filter
An engine needs a free flow of air, and a filter clogged with dust starves it. Open the housing and lift the filter out, then hold it up to the light: a filter that blocks the light is clogged. Tap loose dust off a foam filter and wash it in warm soapy water, then let it dry fully before refitting; swap a clogged paper filter for a clean filter rather than washing it. Check the housing for nests or debris. See gas generator maintenance for a routine that keeps the machine in order.
Clean the carburetor
When a generator sat with fuel in the tank, the fuel in the carburetor can turn to varnish and block the small passages inside. The signs are a generator that starts on choke and dies as soon as the choke opens, or an engine that surges up and down at a steady load. Drain the carburetor bowl, since stale fuel often sits there, then clean the bowl and the jets with carburetor cleaner and compressed air, following the manual for the layout of your carburetor. Do not poke the jets with wire, since a scratched jet changes how the engine runs. If cleaning does not clear the fault, a rebuild kit or a replacement carburetor for your model may be the next move.
Check the oil and the low-oil shutoff
Many generators have a low-oil shutoff that stops the engine when the oil level falls, so check the oil before assuming a deeper fault. Check the level with the dipstick, then top up with the oil grade your manual names if the level sits low. See what oil a generator takes and how often to change generator oil for guidance. If the oil level is fine and the engine still will not start, the shutoff sensor itself may be at fault, and that is a job for a repair shop rather than a home fix.
When it runs but makes no power
An engine that runs well but gives no power at the outlets usually has a tripped breaker on the generator, a loose plug, or a load that exceeds what the generator can supply. Reset the breaker on the generator and check that the plug sits firmly in the outlet. Unplug every load, then add loads back slowly to see whether a faulty tool or appliance trips the breaker. See how to fix a generator not producing power. If the outlets stay dead with no load attached, the fault may sit in the generator head or the voltage regulator, and that is a job for a repair shop. Never feed generator power into a wall outlet or a home circuit: a generator powers tools and appliances through its own outlets only.
Keep it running after the fix
- Run the generator dry of fuel before long storage, or drain the tank and carburetor, so stale fuel never sits in the system.
- Change the oil and clean the air filter on the schedule your manual gives.
- Start the generator now and then through the months it sits idle, under a light load, so seals stay wet and the carburetor stays clear.
- Store it under cover, away from damp, with the fuel valve closed.
See gas generator maintenance for the full routine, and propane generator maintenance if your unit runs on propane.
FAQ: power away from the grid
Why will my gas generator not start after sitting in storage?
Stale fuel is the usual cause. Drain the tank and the carburetor, refill with fresh fuel, check the spark plug and the air filter, and try again.
Can a propane generator be repaired the same way?
Many checks carry over: the spark plug, the air filter and the oil level matter on a propane unit too. The fuel side differs, since propane comes from a tank through a regulator and a hose, so check the tank valve, hose and regulator for damage, and check that the tank holds fuel.
What points to the carburetor as the problem?
A generator that starts with the choke closed and dies as soon as the choke opens, or an engine that surges at a steady load, often points to a gummed carburetor. Drain the bowl and clean the jets with carburetor cleaner before deciding the carburetor needs a rebuild.
When should a generator go to a repair shop?
Take it in when the engine has spark, fuel and air yet still will not fire, when the oil level is fine yet the low-oil shutoff keeps stopping the engine, or when the outlets stay dead with no load attached. Internal engine faults and generator head faults need shop tools and parts.
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