Generator won't start? A step-by-step troubleshooting guide

There's no worse time to discover a generator problem than the first hour of an outage. Fortunately, most no-start problems come down to a handful of causes, and you can check most of them yourself in a few minutes with basic tools. This guide works through them in order, from the most likely to the least. Always follow your owner's manual, which has model-specific procedures and safety warnings.

Safety first: do all troubleshooting outdoors, with the generator well away from the house. Ready.gov and the CDC advise keeping running generators outdoors and more than 20 feet from windows, doors, and vents. Let the engine cool before touching the muffler or refueling, and disconnect all loads before trying to start it.

Step 1: The basics people miss

Before getting out tools, check:

• Engine switch in the ON or RUN position. Many generators have a separate fuel valve and an engine switch, and some combine them in one dial.
• Fuel valve open.
• Choke set correctly: usually closed (full choke) for a cold engine and open for a warm one.
• Fuel cap vent open, if your model has one. A closed vent can starve the engine after a few minutes.
• Loads disconnected. Starting under load can stall the engine.
• Eco mode off for the first start on inverter models, if the manual recommends it.

Step 2: Oil level

Most generators have a low-oil shutdown that stops the engine, or prevents it from starting, when oil is low. That protects the engine but can look like a mystery failure. Put the generator on level ground and check the oil according to the manual. Some models need to be checked with the dipstick screwed in, others with it resting on the threads. Top up to the full mark with the oil type the manual specifies. Overfilling can also cause problems.

Some models have an oil warning light that flashes when you pull the starter. If yours does, oil is the first suspect.

Step 3: Fuel, the most common culprit

Gasoline begins to degrade within weeks to months, especially without stabilizer. Stale fuel leaves varnish that clogs the carburetor's tiny passages. Signs include:

• the engine won't start, or starts and dies;
• surging (revving up and down);
• a sour or varnish smell from the tank;
• fuel that looks darker than fresh gasoline.

What to do:

1. Drain the old fuel from the tank and the carburetor float bowl. Many generators have a drain screw on the bowl. Catch the fuel in an approved container, and take it to a household hazardous waste site.
2. Refill with fresh gasoline.
3. Try starting again. It may take several pulls to draw fresh fuel through.

If it still won't run properly, the carburetor may need cleaning. Many owners can clean or replace a small-engine carburetor, but if you're not comfortable, a repair shop can handle it.

For dual-fuel generators, try switching fuels. If it runs on propane but not gasoline, the problem is almost certainly in the gasoline fuel system.

Step 4: Spark plug

A fouled, worn, or disconnected spark plug prevents ignition.

1. Pull off the plug wire and remove the plug with a spark plug socket.
2. Inspect it. Heavy black carbon, oil fouling, or a worn electrode means it's time for a new one.
3. Check the gap with a feeler gauge against the manual's specification.
4. Replace the plug if in doubt. They're inexpensive. Honda's EU2200i schedule, for example, calls for checking the plug every 6 months or 100 hours and replacing it every year or 200 hours.

To test for spark, use an inexpensive inline spark tester rather than holding the plug against the engine.

Step 5: Air filter

A clogged air filter can choke the engine. Remove the cover and inspect the filter. Foam filters can usually be washed, dried, and lightly oiled per the manual. Paper filters should be replaced if dirty. Never run without a filter.

Step 6: Battery (electric-start models)

If the starter clicks or turns slowly, the battery may be weak. Charge it with a maintainer, or try the recoil starter. Most electric-start portables still have a pull cord. Batteries that won't hold a charge after a full charge cycle need replacing.

Step 7: Spark arrester and exhaust

A spark arrester screen clogged with carbon can restrict exhaust and cause the engine to run poorly or stall. Many manuals call for cleaning it periodically. Honda's schedule, for example, lists every 6 months or 100 hours. Let the muffler cool completely, remove the screen, and brush off the carbon.

It runs, but there's no power

If the engine runs but outlets are dead:

• Check the generator's circuit breakers or reset buttons. An overload may have tripped them.
• Check GFCI outlets on the generator and press reset.
• Try another outlet and another device to rule out a bad cord or appliance.
• On inverter models, check the warning lights. Overload or overheat indicators may need a restart.
• Loss of residual magnetism. Some conventional generators that sit unused for a long time can lose the small magnetism needed to produce voltage. The fix varies by model, so consult the manual or a repair shop.

When to call a professional

Get help if:

• the engine won't turn over, or you hear knocking;
• you see fuel leaking from the carburetor or lines;
• the generator produces abnormal voltage or frequency, if you have a meter;
• carburetor cleaning didn't solve fuel problems;
• the generator is under warranty, since opening it may void coverage.

Prevent the next no-start

• Use fresh fuel with stabilizer, and rotate it.
• Run the generator monthly under some load for 15 to 30 minutes.
• Before long storage, either drain the carburetor or run it with stabilized fuel, as the manual recommends.
• Keep a maintenance log and follow the schedule. See generator maintenance schedule.
• Keep spare oil, a spark plug, and an air filter with the generator.