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12 Reasons a Generator Starts Then Dies (Troubleshoot)

Your generator was running fine, but now it shuts off and won’t stay running.

A generator starts and then dies due to an empty fuel tank, plugged fuel filter, dirty carburetor, clogged fuel line, bad gas cap, dirty spark plug, faulty ignition coil, low engine oil level, or old gas.

Wait for the engine to cool and remove the spark plug wire before performing any repairs. Follow the safety precautions found in your generator operator’s manual.

Generator starts then dies

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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Your Generator Runs Then Shuts Off & Won’t Stay Running

1. Gas Tank is Empty

A gas-powered generator won’t run without gas. I only mention this common knowledge fact because you may be frustrated and skipped checking this obvious reason.

Look for a fuel leak causing you to consume fuel quicker than usual. The fuel gauge may also be faulty showing you have a good fuel supply when you do not. Fix any faulty items.

SOLUTION: Make sure the generator is placed on a flat surface. Add fresh fuel to the generator when it is running low or is out of fuel.

2. Old Fuel

Even if you have enough fuel in the fuel tank, the gas may have gone bad causing fuel restrictions and component failures.

Gas can begin to break down as soon as 30 days after purchase. Most gasoline sold today contains ethanol. This is an alternative fuel that attracts moisture to the fuel system.

Water and ethanol will separate from the gas and sink to the bottom of the tank. This mixture is highly corrosive to the fuel components and engine.

It will leave behind varnish that gums the fuel system and keeps the engine from getting a sufficient amount of gas.

Gas should be consumed within 30 days to reduce the effects of old gas. It can be hard to know exactly how much gas you are going to go through in this time frame especially when you’re not using a generator regularly.

This is why you should add a fuel additive to fresh gas before you add it to the fuel tank. A fuel additive like Sea Foam Motor Treatment will stabilize fuel and reduce moisture so it lasts a little longer.

Follow these tips to get the best fuel results:

  • 4-CYCLE GENERATORS require unleaded gasoline with a minimum 87-octane rating and a maximum ethanol content of 10%. Don’t use gasoline with higher ethanol contents. Don’t mix with oil.
  • 2-CYCLE GENERATORS require a gas and fuel mixture. Mix unleaded gasoline with a minimum 87-octane rating and maximum 10% ethanol content with a premium 2-cycle air-cooled engine oil.
  • Use fuel within 30 days.
  • Don’t leave gas outdoors.
  • Store gas in a dry place.
  • Only buy enough gas you can use within 30 days. If you purchase more than this, add a fuel additive to stabilize your gas.

SOLUTION: Drain old gas into a container to be disposed of properly. Add fresh fuel with a fuel additive to stabilize and clean the fuel system.

3. Plugged Fuel Filter

Many portable generators use a filter installed at the bottom of the fuel tank. This type of filter is not easily accessible.

Other generators will use an inline fuel filter inserted between the fuel lines to strain fuel before it gets to the carburetor. Its purpose is to keep dirt and other debris from passing through the fuel system.

Dirt trapped by the filter can build up keeping fuel from flowing through the filter. The engine may die because it isn’t getting sufficient fuel.

SOLUTION: For an inline fuel filter, stop the fuel flow using the fuel shut-off valve or fuel hose pinch pliers. Remove the fuel filter and install a new one. Turn the fuel flow back on.

For a filter inserted at the bottom of the fuel tank, the fuel must be removed from the tank before removing the components at the bottom of the tank to locate and replace the filter.

4. Fuel Line Blockage

Old gas can leave behind gummy deposits that stick to the fuel lines. This narrows the opening in the line keeping a good flow of fuel from getting to the carburetor.

Use the fuel shut-off valve to start and stop fuel while checking the flow coming out of a section of the fuel line.

SOLUTION: To remove a restriction from the line, remove the fuel line from the generator and spray carburetor cleaner into the line to help loosen the clog.

Next, blow air through the line using compressed air until the clog is removed. Repeat as necessary.

Reinstall the line. If you can’t get the clog removed or you find your fuel lines are dry and cracked, you can easily replace it with a new fuel line purchased online or from your local hardware store.  

5. Bad Fuel Pump

Most portable generators don’t require a fuel pump. However, some generators will use a fuel pump when the carburetor sits higher than the fuel tank.

A vacuum fuel pump uses the vacuum off the engine to move fuel from the fuel tank to the carburetor. When a fuel pump fails to work, the carburetor won’t get enough gas and the generator will die.

Before you begin testing the fuel pump, confirm you are getting fuel to the inlet port on the pump. Then remove the line from the carburetor and place it in a container.

Start the engine and watch for a steady or pulsating flow coming out of the line.

SOLUTION: Replace a fuel pump that is unable to provide a constant flow of fuel to the carburetor.

6. Dirty Carburetor

The carburetor is responsible for mixing the right amount of fuel with the right amount of gas needed for combustion.

It is common for old gas to leave deposits that clog the fuel passageways or cause internal carburetor parts to stick. This can fail to provide sufficient fuel to the engine and your generator may shut down.

SOLUTION: Clean your carburetor to remove gummy deposits and crusty buildups that remain from running old fuel and fuels with ethanol. If your carburetor is excessively dirty or has broken components, you may have to rebuild or replace it.

7. Wrong Choke Setting

A generator with a cold engine must be started with the choke closed to restrict air. Once the engine warms up the choke must be adjusted to the open position to allow more airflow so the engine continues to run.

SOLUTION: If your engine starts and then shuts down right away, you need to make sure the choke is off and in the open position.

8. Clogged Air Filter

The air filter is essential to keep dirt from entering the air intake allowing dirt to wear the engine. This is an important part that must be routinely checked to keep it in good condition.

For the average homeowner, I recommend replacing the air filter annually and cleaning it a few times a year. When you notice the filter is extremely dirty or damaged, you must replace it.

You will definitely need to replace it more often if you are running the generator in dry dusty conditions.

If you are not cleaning and replacing the filter regularly, the filter can become plugged with so much dirt that the engine won’t get sufficient air. It can overheat and cause extensive permanent engine damage.

SOLUTION: If you find your air filter is plugged, clean it using the procedure below for your type of air filter.

Because air filters vary by manufacturer, refer to your operator’s manual for cleaning instructions for your type of air filter.

9. Bad Gas Cap / Fuel Tank Vent

The fuel tank needs to have a vent so air is able to pass through it to equalize the pressure in the fuel tank.

When the vent is plugged, air won’t enter the tank as fuel is consumed. The tank will form a vacuum and won’t allow fuel to get to the carburetor. This will keep the generator from running.

You can determine whether the fuel tank vent is your problem by using a pressure gauge. Don’t worry if you don’t have a pressure gauge.

Follow this method to determine if you have a vent problem:

  • Loosen the fuel cap.
  • Start the generator. If the generator runs well, try to replicate the issue by retightening the fuel cap.
  • Allow the generator to continue to run to see if it begins to run sluggishly and/or shuts down.
  • If the engine acts up and doesn’t run strong until you loosen the cap to allow air into the tank, you most likely have a problem with the fuel tank vent.

The fuel tank vent may be built into the gas cap. It may also be an independent vent installed on the top of the fuel tank.

SOLUTION: Replace the gas cap or rollover valve tank vent (depending on your model) when you find the fuel tank is no longer venting properly.

10. Dirty Spark Plug

The spark plug provided the spark required to get it started, however, if the plug is very dirty or damaged, it may have intermittent spark problems that will cause the generator to sputter and die.

SOLUTION: Remove the spark plug and check its condition. If the tip is very dark in color, the electrode is worn or the porcelain is broken, you must replace the spark plug with a new one.

If it appears in good condition, clean it with a wire brush and check the electrode gap and securely attach the spark plug wire. A loose wire or incorrect spark plug gap can also cause the generator to quit running.

11. Bad Ignition Coil

Before checking for a bad ignition coil, make sure your spark plug is in good condition. The ignition coil provides voltage to the spark plug so it can start the engine.

If the spark plug isn’t able to fire due to a bad spark plug or ignition coil, the engine will not start.

SOLUTION: Check the continuity of the ignition coil. If you find a break in the continuity, replace the ignition coil.

12. Insufficient Engine Oil Level

Your generator may run for a while and then suddenly stop. Check to see if the low engine oil light is on.

When the oil level is low, your generator may have a sensor that will shut it down to protect the engine from damage. It will not restart until the engine oil level is corrected.

It may be frustrating that it won’t keep running. However, the generator shutting down is a good thing.

Continuing to run an engine that is low on oil can result in significant engine damage because a lack of sufficient lubrication will cause friction to build in the engine. The engine can become so hot that the parts can begin to melt.

SOLUTION: To check the engine oil level, begin by placing the generator on a flat-level surface. Remove the oil fill cap and wipe off the dipstick with a clean cloth to remove the oil.

Reinsert the dipstick into the oil-fill tube, but don’t screw on the cap. Remove it and look at the oil level on the dipstick. Ensure it is in the full range on the dipstick.

If it is not, correct the engine oil level by removing or adding a little air-cooled engine oil until it is at the correct level.

When you find you have the correct engine oil level and the low oil sensor stays on, you may have a faulty sensor. It’s best to take the generator to a service center to be repaired.