Generator Won’t Start? 11 Common Causes and Fixes

Most generators that won’t start have one of a few simple problems: the fuel valve or engine switch is off, the gas is old, the oil is low, the choke is set wrong, or the carburetor is gummed up from sitting. Work through the checks below in order. The first five take a couple of minutes and fix most no-start problems.

Quick checklist

1. Engine switch ON and fuel valve OPEN
2. Fresh fuel in the tank (or a full propane tank with the valve open)
3. Oil at the full mark, with the generator on level ground
4. Choke closed for a cold start
5. Nothing plugged into the outlets
6. Battery charged (electric start)
7. Spark plug clean, gapped and its wire attached
8. Air filter clean
9. Carburetor and fuel line clear
10. Low oil sensor or CO shutoff not tripping

That list follows the “engine will not start” troubleshooting table in generator manuals like Champion’s 6250-watt dual fuel owner’s manual, which lists no fuel, a faulty or loose spark plug, low oil, a closed fuel valve, the engine switch off, old or watery fuel, and a flooded engine.

1. The engine switch or fuel valve is off

It’s the most common miss. Many generators have a separate engine switch and fuel valve, and some combine them in one knob. Check both, and if your gas cap has a vent, open it.

2. The fuel is empty, old or contaminated

Check the tank first. If the gas has been sitting for more than a month or two without stabilizer, it has probably gone stale, and stale gas is the top reason a stored generator won’t start, according to Consumer Reports. Drain the tank and the carburetor bowl into an approved container and refill with fresh gas. On a propane or dual fuel generator, make sure the tank has gas, the tank valve is fully open, and the fuel selector is set to propane. See how much gas a generator uses.

3. The oil is low, or the generator isn’t level

Most portable generators have a low oil shutdown that won’t let the engine run when the oil is low. Put the generator on flat, level ground and check the oil with the dipstick or fill plug. Top it off with the oil type in your manual. On a slope, the sensor can read low even when the oil is fine.

4. The choke is in the wrong position

For a cold engine, close the choke (often labeled START or CHOKE). Once it fires, move the choke gradually toward RUN. If the engine is already warm, start it with the choke open or half open. If you smell gas after many pulls, the engine may be flooded: open the choke, wait about 10 minutes, and try again.

5. Something is plugged in

Unplug all cords and turn off the main breaker on the generator before starting. A load on the generator can make it hard to start and can trip the breaker right away. Plug things in once it’s running and warmed up. Here are the extension cords we recommend for generators.

6. The battery is dead (electric start)

If the electric start clicks or does nothing, use the recoil pull start if your generator has one. Once running, many generators recharge the starter battery. Otherwise, charge it with a battery charger. Some generators can be jump-started from a car battery; follow your manual and connect the last clamp to bare metal on the generator frame, away from the battery.

7. The spark plug is fouled or loose

Make sure the spark plug wire is pushed on firmly. Then remove the plug with a spark plug socket. If it’s black and sooty, oily, cracked or worn, replace it. If it looks good, clean it and set the gap to the spec in your manual. To check for spark, reconnect the plug to its wire, hold the metal base against bare metal on the engine (away from the spark plug hole and any fuel), and pull the starter. You should see a blue spark.

8. The air filter is clogged

A dirty air filter chokes the engine of air. Pull it out and look. Foam filters can be washed and lightly oiled; paper filters should be replaced. Here’s how to clean your generator.

9. The carburetor is gummed up

If the generator sat with gas in it, old fuel can leave varnish that blocks the carburetor’s tiny jets. With the fuel valve off, remove the carburetor bowl (usually one bolt on the bottom), clean out the gunk, and clear the main jet with carburetor cleaner and a thin wire or a single bristle. If that doesn’t work, a carburetor rebuild kit or replacement carburetor is often inexpensive. To prevent it, run the generator dry or use fuel stabilizer before storing it.

10. The fuel line, filter or valve is clogged

Pull the fuel line off at the carburetor (with a container underneath) and open the fuel valve. Gas should flow freely. If it doesn’t, check the in-line fuel filter and the screen in the fuel valve or tank outlet.

11. The low oil sensor or CO shutoff is stopping it

If the oil is full and the generator is level but it still dies within a few seconds, the low oil sensor may be faulty. Here’s how to test the low oil sensor. Never run a generator with low oil. Many newer generators also have a carbon monoxide shutoff that stops the engine if CO builds up around it. If a CO warning light is on, move the generator into open air, at least 20 feet from the house, before restarting.

Still won’t start?

If the engine has fuel, spark and air but still won’t run, it may have low compression or an ignition coil problem. That’s a job for a small-engine shop or the manufacturer’s service center. If you have an RV generator, see why an Onan generator starts then shuts down. If the status light is blinking, look up the number in our Onan fault code list.

Related guides: Why is My Generator Not Producing Power and Can Generators Overheat.

FAQ

Why does my generator start and then die?

Usually low oil, a choke left closed, a partly clogged carburetor or a fuel cap vent that’s closed. Check those first.

How do I start a generator that has been sitting for years?

Drain the old fuel, clean or replace the carburetor, change the oil and spark plug, check the air filter, and charge or replace the battery before trying to start it.

Can I use starting fluid on a generator?

Many manufacturers advise against it. A short spray into the air intake can show whether the problem is fuel delivery, but don’t make a habit of it.