10 Common Reasons Your Generator Won’t Start

There’s nothing more frustrating than pulling your generator out of the garage only to find that the engine doesn’t turn on like it’s supposed to. Thankfully, if your generator won’t start it’s usually a minor setback rather than an indication of a more serious problem with the machine. 

The best place to start with troubleshooting your generator is with some of the most common causes of starting issues. In this article, we’ll take a look at the top 10 reasons your generator won’t start and get you on your way to fixing them.

Top Reasons your Generator Won’t Start

1. Low on fuel
2. Low on oil
3. Battery is dead
4. Cables are plugged in
5. Choke is too open/closed
6. Dirty air filter
7. Bad spark plug
8. Carburetor is clogged
9. Fuel valve or line is clogged
10. Low oil sensor is malfunctioning

1. The generator is low on fuel

It may seem obvious, but it’s worth checking whether your generator has gasoline in the fuel tank. If not, that’s a clear reason why your engine would fail to turn over. If you’re using propane to fuel your generator, make sure that the tank has enough gas and that all of the valves on the tank and tubing are opened.

Keep in mind that using stale gasoline – typically any gasoline that’s older than two months – can be very damaging to your generator’s engine. If you have stale gasoline in the tank, you’ll need to empty out the fuel tank and the carburetor, then refill with fresh gas. Be sure to use a kit to safely remove all of the bad fuel.

2. Your engine is low on oil

Oil is just as important as having fuel for running your generator. Most modern generators are equipped with a sensor that will automatically shut down your generator when oil levels are low to protect the engine. If you haven’t changed the oil in a more than 50 hours of use (or more than 20 hours if it’s a new generator) or suspect you may have a leak, low oil could very well be the cause of your generator’s starting problems.

You can check the oil level using the dipstick on your generator, which may be located inside the crankcase. If the oil is low, check your manufacturer’s guidelines on what type of engine oil is suitable for your generator. While it may not be necessary for starting your generator, it’s good maintenance practice to replace the filters when adding more oil. We’ve written a helpful guide if you’d like to bypass the low oil sensor on your generator.

3. The battery is dead

If your generator has an electric starter in the form of either a push-button or a remote, the first thing you need to check is whether the battery for the starter is the problem. Just like in a car, if your generator’s battery has run out the electric starter can’t work.

The easiest way to troubleshoot this is to try starting with the auxiliary recoil starter if your generator has one. If that works, you can simply charge up the electric starter battery via the 12-volt DC outlet on your generator once it’s running.

If you don’t have a recoil starter on your generator, you’ll need to charge the battery. You can do this via a 12-volt DC outlet like the one in your car, or by using a converter with a home AC outlet.

Alternatively, you can use jumper cables to jump-start your generator battery using your car battery. The procedure is the same as for jump-starting another car’s battery: Attach the cables to your car and generator using the metal frame of your generator as the fourth connection point, turn on your car, and then try starting the generator.

If these methods still don’t work, the reason your generator won’t start probably isn’t because of a dead battery.

4. There are cables plugged into the generator

Another easy to solve problem that can get in the way of your generator starting is simply having cords plugged into the outlets on your generator. Whenever starting the generator, you shouldn’t have anything plugged in – even extension cords that don’t have any appliances attached at the other end.

5. The choke is too open or too closed

The choke controls the amount of air that’s flowing into the carburetor during startup. If your generator is trying to startup but the engine can’t seem to turn over, the problem may be too much or too little air mixing with your fuel during combustion.

When starting a generator cold – that is, it hasn’t been running for at least the past few hours – the choke should be set all the way closed. The closed position is often labeled as the “start” position on generator chokes for this reason. Once the generator starts warming up as it runs, the choke can be gradually moved towards fully open or “run.”

On the other hand, if you had been running your generator recently and just turned it off briefly, the engine will still be warm. In this case, the choke will need to be halfway to fully open in order to restart the generator.

6. Your air filter needs to be replaced

If adjusting the choke seemed to help, but didn’t solve the problem, your air filter may be to blame. If the air filter is clogged with dust and debris, your carburetor won’t receive enough air for combustion.

The air filter is generally easy to access and inspect visually. If it looks dirty or clogged, try replacing it and moving the choke back to the proper starting position.

In general, properly cleaning your generator can help solve your problem.

7. The spark plug is having problems

If the engine won’t even attempt to turn over during startup, the problem may lie with your spark plug. In order to check your spark plug, start by removing it from the engine with a spark plug socket. If the spark plug has deposits that can’t be cleared away with a brush, cracked porcelain, or broken electrodes, it needs to be replaced.

Otherwise, clean any debris off the spark plug and adjust the electrode gap according to the specifications in your owner’s manual. You can double-check that the spark plug is working by holding it against the engine’s crankcase while pulling the recoil starter if your generator has one – a working spark plug will produce blue sparks. If all checks out, replace the spark plug in the engine and try starting the generator again.

8. The carburetor is clogged

If you didn’t drain the carburetor before putting your generator away for a month or more of storage, this is likely the culprit for why you’re having starting issues now. Old gasoline will form clogs in the carburetor, making it impossible for new fuel to get through.

To clean out the carburetor, close the fuel valve and then remove the bowl at the bottom of the carburetor. Use a brush and towels to clean out any fuel debris and use a sewing needle or safety pin to clean out the brass jet nozzle. Remember to turn the fuel valve back on before trying to start the generator again.

9. The fuel valve or line is clogged

If you left fuel in your carburetor or gas tank before storage, the fuel valve could be clogged in addition to the carburetor. First, make sure that the fuel valve is open and that if your generator has a vacuum relief valve above the gas tank, that gets opened too.

If that still doesn’t work, you can unplug the hose from the inlet side of the fuel valve to check whether gasoline is able to flow freely through your fuel line – make sure you have a bucket handy to collect any flowing fuel when you do this. If your generator has an in-line filter between the fuel valve and the carburetor, it’s a good idea to pull that out and visually check it for clogs as well.

10. The low oil sensor is malfunctioning

The low oil sensor is designed to keep your generator from starting when the oil is low – but if it malfunctions, it can keep your generator from starting no matter how much oil you have. Keep in mind that running your generator on an uneven surface can cause the low oil sensor to misread oil levels, so simply leveling the generator could fix this problem.

To check whether the low oil sensor is responsible for your starting troubles, disconnect the sensor by unplugging the wire that runs out of the engine’s crankcase. If the generator starts after disconnecting this, the low oil sensor was very likely the culprit. Usually, the sensor will work if it is plugged in again after running the generator for a few minutes, although if this fails the sensor will need to be replaced – which can be a time-consuming task that involves taking apart your engine.

Never remove the low oil sensor to mask a problem with low oil. Running your generator at low oil levels can severely damage the engine and pose a significant hazard. Before disconnecting the low oil sensor, ensure that your oil is topped off and your oil filters are not clogged.