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17 Reasons why Generator won’t Start [and Solutions]


The generator doesn’t start? Don’t panic! It is quite common for generators not to start from the first try!

Why would your generator not start when you need it the most? It could be anything from a triggered low oil sensor to a more complicated problem, like a clogged fuel delivery system. Many problems can be solved and you will be up and running in no time!

Now, let’s take a deep breath and troubleshoot:

Basic issues

  • You are out of gas!
  • You are low on oil.
  • Your fuel valve is closed.
  • Your choke is in the wrong position.
  • Dirty air filter
  • Are you starting it with a load?

Weather problems

  • Hot summer day
  • Cold winter morning

Fuel system problems

  • Fuel delivery system blockage
  • Fuel delivery system contamination
  • Your fuel valve is clogged
  • Your carburetor is clogged
  • You need to change the fuel filter

Ignition problems

  • Are you getting a spark?
  • Is your spark plug flooded?

Electrical problems

  • Your battery is dead (electric start).
  • Residual Magnetism

Now, let’s go over the above problems in greater detail:

Basic problems (something easy to forget)

1. Your generator could be out of gas!

Sounds basic and simple, but maybe you just forgot! This problem is EASY to solve, just add some fresh gasoline. Do NOT use gasoline that is more than 2 months old! It will clog your system and cause more problems while running a generator…

It is also a good idea to use fuel WITHOUT ethanol in it, along with a gas stabilizer.

2. You are low on oil

Many generators are equipped with a low-oil sensor and will NOT let you start a generator if triggered! Good idea, right? So, if your generator is not starting, you may need to check your oil level.

You will probably also notice a “low oil” indicator light on the control panel of your generator like this:

There could also be a digital indicator:

The dipstick on your generator (which may be placed within the crankcase), may be used to check the oil level. If the oil level is low, your manufacturer should mention in the owner’s manual which oil is best for your generator.

Add oil if necessary and check oil filters as well. They should be changed after certain usage intervals (consult manual again) and if you did not do it when it was necessary, you may want to change them now.

On the maintenance side, if you haven’t replaced oil in more than 50 hours of usage (or more than 20 hours if it’s a new generator), you may have a problem starting your generator as well. Pay close attention to oil leaks and the reason behind the “low oil” situation.

It’s also a good idea to make sure your generator is on a flat surface and if it’s not, move it (uneven surface can cause low oil sensor to trigger as well). It is also possible that your sensor is NOT WORKING properly!

This is a way to test it:

  1. Step 1. Make sure your oil is full and your oil filters aren’t blocked.
  2. Step 2. Disconnect the sensor wire from the side of the crankcase to verify this (the wire’s position varies significantly from generator to generator).
  3. Step 3. Start your generator and if it works, you have a problem with the sensor.

The low oil sensor will disconnect a spark to keep your generator from starting and if you get the spark back after disconnecting, then the problem is the sensor. Now, you can try running the engine for a few minutes (few times) with this disconnected oil sensor before reconnecting the wire and see if it solves the problem.

If that doesn’t help, you will need to replace the oil sensor (which requires disassembling your engine).

** Warning! Running your generator with low oil levels can cause serious engine damage and represent a safety risk. Never remove the low oil sensor to conceal a low oil problem.

3. Your fuel valve is CLOSED

If your generator is not getting any gasoline, it will NOT start! Check if your fuel valve is turned on! It looks like this:

It should be in an ON position:

** Important! In DUAL fuel systems, make sure you open the appropriate connection (valve) and close the other one!

4. Your choke is OPEN

During starting, the choke regulates the amount of air entering the carburetor. The choke should be placed all the way to the CLOSED / START  or ON position (when starting a generator after a long break).

The issue with your generator not starting may be too much air mixing with the fuel during combustion and choke controls just that! If your generator ALREADY WARMED UP, and you need to start it again (after adding some fuel), you can put chock to HALF-WAY POSITION or even OPEN / RUN / OFF.

This choke lever may be located in a few different locations depending on the type of your generator. It may be located right above the air filter on the side of a generator:

The choke could also be incorporated into a knob like this:

5. When was the last time you checked your air filter?

Once again, sounds basic, but air filters need to be checked and cleaned (or replaced) once in a while. Locate the air filter on your generator and perform a “Filthiness check”.

It’s possible that if it’s blocked badly enough, it’ll prevent your home generator from starting. First, you might try cleaning your air filter by smacking it against a wall, counter, or even the floor.

That will take the dust out. If the dirt just will not budge, or if the air filter is worn through or damaged, you will need to get a new filter. Your filter could also be washed:

Your carburetor will not get enough air for combustion if the air filter is blocked with dust and debris. If you need to replace the filter, check the specs in your generator’s owner’s handbook to be sure you get the right one.

** Important! Do NOT run a generator without an air filter! If you operate the generator without an air filter, your carburetor and perhaps the engine will be damaged.

You can try starting it without one to see if the problem persists and once you figured out that the filter is the problem, turn the generator OFF and replace or clean your air filter. Just running without filter will NOT solve your problem and create a bunch of new ones!

6. Are you trying to start with a load?

Another simple problem that might prevent your generator from starting is having cables hooked into the outlets on your generator. You should NOT have anything connected while starting the generator (including extension cables with no appliances attached at the other end).

This is what you will probably read about in your owner’s manual:

Image source.

Basically, most of the owner’s manuals tell you that you need to let your generator warm up before connecting the load:

Source PDF.

Just to be on the safe side, do not plug ANYTHING in until it’s up and running!

To summarize this section, there are quite a few things to remember before starting your generator correctly, so let the owner’s manual be…

… at your service!

Here is a good video on common generator problems and how to solve them:

Fix a very common problem on a generator


Weather-related problems (something you don’t control)

7. Too hot outside (vapor lock)

High ambient and engine temperatures can cause vapor lock in the mechanical fuel pump, carburetor, and fuel lines. Vapor lock may prevent your generator from starting and it can be caused by a number of reasons:

  • High temperatures in summer
  • High altitude area
  • Gasoline enhanced with ethanol
  • Clogged or faulty fuel supply system (filter, tank vent, etc)

This issue is very common in engines with a carburetor. It happens when the fuel delivery system overheats and vaporizes too rapidly. As a result, the accumulated gas bubbles clog the fuel pipes and don’t allow the fuel to get to its destination.

Here is a good explanation of what to do in this situation:

How To PREVENT VAPOR LOCK In Your GENERATOR, Small Engines, And Carbureted Classic RV Or VAN!

8. Too cold outside

When the temperature drops below -22 F (or -30 degrees Celsius), it is sure not easy to get a generator going! When a generator won’t start, it’s usually because we didn’t allow it enough time to preheat.

If you got ice in your fuel line, it is no fun at all and your generator will NOT start! You need to do something to warm a generator up before starting. You can try to pre-heat your generator:

Cold start, had to pre heat 3 times

It’s critical to have a well-insulated generator shed and, preferably, some type of heater when you rely on generators in a cold-weather region. You can install a small wall heater in your generator shed.

Another alternative is to leave your heater on at a low setting all the time. Don’t forget that good ventilation is still important to avoid carbon monoxide buildup.

Fuel related problems

There are several reasons why your generator may not be getting enough fuel to start the engine:

  • Your fuel is old and stale (more than 30-60 days old)
  • Your fuel is contaminated with water
  • Your fuel valve is clogged.
  • Your fuel filter is dirty
  • You have a clogged carburetor.

9. Fuel delivery system blockage

If the fuel valve is open, but no gasoline is coming through, you may have a problem with a clogged fuel delivery system. Fuel goes stale if stored for an extended length of time and if it’s inside your generator, the fuel valve, as well as the carburetor, might become blocked. When this happens, the gasoline will never even reach your generator!

It is also a good idea to check for clogs, twists, or leaks in your fuel line. You may want to verify whether gasoline can flow freely through your fuel line by unplugging the hose from the intake side of the fuel valve.

Remove the in-line filter between the fuel valve and the carburetor and visually inspect it for blockages. Replace filter if needed. You can use a special kit to carefully remove all of the contaminated gasoline and clean your fuel tank.

10. Fuel delivery system contamination

Another reason your generator may not start is if your fuel contains water. You will need to get rid of it:

HOW-TO Quickly Start A Generator That Won't Start!

11. Your fuel valve is clogged

If your generator is not starting, there might be an issue with the fuel valve. Fuel flow from the gas tank to the carburetor is controlled by the fuel valve and it has to be in the ON / OPEN position (like mentioned above).

If the gas tank is full and the valve is set to the OPEN position, but no gasoline is going to the carburetor, first of all, open the vacuum relief valve on top of the gas tank to make sure there is no excess pressure buildup. After that try checking the pipe by unplugging it from the valve side and if the gasoline starts coming out, your fuel valve may need a replacement.

12. Your carburetor is clogged

Old fuel becomes stale and sticky, and if is left inside the carburetor, it would leave a gummy residue all over! Here is a good video on how to clean a carburetor:

How to Clean a Generac Briggs and Stratton Nikki Carburetor - Generator Hunting for Fuel

To avoid this type of problem in the future, run your generator at least once a month and always drain the gas tank and carburetor before storing it for lengthy periods of time.

13. Clogged fuel filter

Fuel filters can also get clogged and that is exactly what they are supposed to do! The purpose of the filter to keep debris out of the fuel line. If it’s clogged, just replace it.

Its location is usually inside the gasoline tank or in the fuel line:

Make sure you’re in a safe place where there’s no open flame or fire. When removing or checking a filter, wear safety glasses to protect your eyes from liquid gasoline or fuel vapors.

If the filter is placed inside the tank, the tank must be drained before the filter can be removed for maintenance or replacement. Use a dry towel to hold the filter and collect any dripping gasoline.

** Important! Make sure you read the owner’s manual before attempting to change the fuel filter yourself. If you’re unsure about what you are doing or have more questions, see an authorized dealer.

Here are some basic guidelines on filter replacement (if your filter is located on the fuel line):

  • Step 1. Close the fuel valve. If your generator doesn’t have a valve, use a fuel line clamp to clamp the gas line. Do not PINCH the fuel line, as it may get damaged.
  • Step 2. Use needle tip pliers to remove the metal clamps on each side of the filter and slide the filter out of the gasoline line.
  • Step 3. Shake the filter over a clean cloth to remove any residual fuel, then wipe any residue from the outside of the filter with the cloth.
  • Step 4. Look through one end of the filter while keeping it at a safe distance from your face. From the opposite side, you should be able to see light coming through.
  • Step 5. Replace the old filter with a new gasoline filter if you notice any debris blocking the way of the fuel.
  • Step 6. Carefully reattach the metal clamps on both sides of the gasoline filter while replacing it.
  • Step 7. When the fuel filter is secure, remove the clamp from the fuel line or reopen the fuel valve.
  • Step 8. Look for any leaks. If any are discovered, the device should not be used and the gasoline line should be replaced (it probably has few cracks that will be noticed upon close inspection).

Ignition problems

14. No spark

You need a good spark to be able to start your generator! Are your spark plugs scratched or worn? Are they producing a good spark?

It’s possible that the electrodes have corroded or been damaged. In this case, use a spark plug tester to see if your generator isn’t starting due to defective spark plugs.

This device is not expensive and will tell you exactly if you need to get new spark plugs (paid link below):

15. Flooded spark plug

Your spark plug could be flooded with fuel and therefore it may not produce the needed spark. The reasons for this could be too much gasoline added or a clogged carburetor is leaking fuel.

When you take the spark plug out, it will be wet and you will actually be able to smell the gasoline To fix this issue, all you have to do is remove the spark plug and just let it dry or wipe it with a cloth.

Drying it out with compressed air could speed up the process. After that reinstall it and try starting the engine.

Electrical problems

16. Dead battery

If your generator is equipped with an electric starter, you may simply have a dead battery and this is why it is not starting! This happens to car batteries as well:

“If we don’t use them, we lose them!”

The battery in electric start (push-button, key, or a remote) generators may lose its charge over time. You can also use a multimeter to check the battery in your generator and confirm the problem.

If this occurs, just start the generator using the pull starter (recoil) and your battery will recharge. Many generators come with a recoil start along with an electrical one.

If the device doesn’t have a backup recoil starter, you may need to use an external battery charger. Here is a reasonably priced battery charger from Schumacher (paid link).

Jumping a battery from your vehicle may not be a bad idea as well. You will need to use regular jumper cables and connect them in the following way:

  1. Step 1. Connect negative (-) black clamp to negative (-) post of the vehicle battery and another end to the frame of the generator (bare unpainted metal).
  2. Step 2. Connect positive (+) red clamp to positive (+) post on the battery of both vehicle and a generator
  3. Step 3. Start the car and wait
  4. Step 4. Attempt starting the generator
  5. Step 5. If works, leave the generator ON until it starts producing 120VAC and connects to the transfer switch
  6. Step 6. After that, it will start producing 12-volts for your battery and you can disconnect the jumper cables.

** Warning! If you don’t know what you doing, seek professional assistance. When jump-starting, never leave your vehicle and generator unattended!

Your generator’s battery can also be charged from a 12-volt DC outlet (in your car) or AC outlet at home along with a converter-charger (paid link).

If none of these approaches work, the issue is most likely not a dead battery, and let’s go to the next subject, which is…

17. Residual Magnetism

The lack of residual magnetism is also a common problem if your generator is refusing to start. Check out this article for more details: “Why is my Generator not Producing Power?

Click on the white button above to find your electrician!

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