Generator Won’t Start

You’ve tried starting your generator, but it won’t turn over.

There are a lot of potential problems that could be keeping your generator from starting, from a bad battery to faulty wiring.

Before you give up and take your generator in for repairs, try troubleshooting the problem yourself. Our guide will walk you through the most common causes why your generator won’t start so you can get your machine running again.

What would cause a generator not to start?

Any troubleshooting exercise starts by checking the most obvious and likely reasons and gradually proceeds toward the more complex ones. In this way, you can rule out the causes by the process of elimination in a systematic way. The most important clues are obtained from the following three queries:

  1. Are there any leaks? – Fuel, grease, oil, or water provide tell-tale signs of cracks, loose connections, etc.
  2. Is there any smoke? – Look out for the abnormal quantity or the color of the smoke. Is the quantity increasing or decreasing? Does it clear itself out after the engine has run for some time?
  3. Are there any abnormal sounds? – The type of sound can provide an important clue towards the existing fault.

Let us now provide you with the most common reasons your generator won’t start, beginning with the most obvious ones.

Is the fuel tank empty?

As highlighted in the previous section, start by checking the most obvious, the availability of the fuel itself. Check if the gas tank has enough gas to run. If the levels are low, fill the fuel tank after ensuring that the engine has cooled down.

Old gasoline left in the gas tank for more than a couple of months without a stabilizer is termed “stale gasoline” and can result in hard starting, varnish formation, and damage to the engine.

You should drain the fuel tank and fill it with fresh gasoline. Environmental Protection Agency (EPA) permits using the drained old gasoline in your car’s gas tank by mixing it with 50% fresh gas.

If you notice some debris in your generator’s tank, look out for any crack or hole. If you find one, go for a new tank. Don’t repair a damaged tank, as it risks leakage, fuel contamination, and even fire. Over time, these cracks develop due to long-term exposure to the sun, other elements, and the weight of other parts of the generator’s engine.

It’s low on engine oil.

It is a good habit to check the oil levels every time you start your engine after a gap. You also get a more accurate reading of the oil level when the engine is cold, and most of the oil is still in the crankcase. Most manufacturers advise you to change the oil after 25 hours of operation.

Most modern generators have a low oil sensor to warn you and automatically shut down the engine to protect it. You can manually also check the oil level with a dipstick. The oil mark should be between the two lines marked on the dipstick. Do not overfill the crankcase because too much oil can cause engine damage. Refill with the engine oil recommended by the manufacturer, if necessary.

The Electrical Start Problem.

If your portable generator has electric and remote start features, it is very likely that the generator battery or the associated electric starter circuitry has developed some fault.

Is your Battery Dead?

Start with checking the condition of your generator‘s battery. If you have not used your generator for a long time and have not changed the battery, you may be experiencing a dead battery that has continuously discharged over time to a very low charge.

Use the recoil rope to start your generator and charge your generator battery with the 12V system.

If your generator does not have the recoil provision, use the third-party chargers, or in the worst case, use your car battery to jump-start the generator battery.

Problems with the electrical start circuit

If the generator starts with the recoil rope and your battery is also healthy, the problem must lie with the electrical circuitry associated with starting the engine. The following issues are likely.

  1. Bad starter or On-Off Switch
  2. Faulty wiring between the starter switch and the solenoid.
  3. Something is not right between the solenoid and the motor.

Fuel Line Issues

After checking the three very obvious reasons, let us look at the possible causes system-wise, starting with the fuel system and fuel line. If no fuel reaches the carburetor, there may be a problem with the fuel valve or the fuel line.

Is the Fuel shutoff valve closed?

Check if the fuel shutoff valve is closed. Open if found closed. If you use propane, check for closed valves on the tubing in addition.

Is the fuel tank cap clogged or unvented?

Many tanks have a vented fuel cap to prevent vacuum formation in the fuel lines. This vented gas cap has a pressure-activated unidirectional vacuum relief valve that opens slightly once the vacuum formed inside the tank exceeds a preset limit till the equalization of the pressure. This vacuum formation is due to the fuel displacement inside the tank.

After equalization of pressure by air intake, the valve closes again. If the vent cap is clogged, the vacuum in the line will not allow the fuel to move freely. On the other hand, any damage to the vent cap or leak may allow dirt or even water to enter the fuel tank.

Is the fuel diluted with water?

As discussed in the last point, check for leaks in the vent cap and water in the tank. If water is there, you must drain the old fuel and, check the tank for any other leakages or damages. Replace the tank or the vent cap, whichever is damaged, before filling it back with the fresh fuel.

Is the Fuel Line Or fuel Valve clogged?

If none of the above has been successful, unplug the line from the fuel valve’s inlet to check the fuel’s free flow up to this point. Of course, keep a bucket handy before disconnecting the line.

Check for the clogged fuel valve, and balance fuel lines till the carburetor. Make sure to check the fuel filters between the valve and the carburetor.

Carburetor Issues

Having ruled out the general and the fuel line issues, it is time to focus on the carburetor. We discussed the carburetor’s functioning in our article on “how do portable generators work.” You may read the article to get initial insights if you are new.

Generator Won't Start - Carburetor Functioning

Is the carburetor clogged or air locked?

If you use your portable generator only during power outages, it is always recommended to drain out the fuel before storing your generator. Else, due to evaporation, a thick and sticky coating is formed that may result in a clogged carburetor.

A clean and well-adjusted carburetor and linkages will go a long way in ensuring a smooth-running engine. Particularly the linkages to the throttle and choke plates can stick due to dirt, or the setting of mixture screws could be affected by the vibration or the wear and tear. The fuel and the air passages can also get blocked due to dirt.

To check, remove the spark plug and its lead and pour a teaspoon of fuel directly into the cylinder. Re-insert the spark plug and try starting the engine. If the engine runs briefly before stopping, you definitely need to overhaul the carburetor.

Shut off the fuel valve and open the drain valve at the bottom of the carburetor’s bowl to remove the stale fuel. Depending on the condition, you may have to remove the entire bowl and clean it with a brush or use the recommended carburetor cleaner. Clean the main brass jet nozzle with a needle or spray a carb cleaner on the jets and orifices.

If none of this works, and the problem is zeroed down to the clogged carburetor, you may have to ultimately replace it, as shown in this video.

Is the engine flooded?

Engine flooding happens when the float valve in the bowl does not operate to restrict the inflow of new fuel into the carburetor. This could be due to

  • The crack or a hole in the float causes the fuel to fill the float, making it heavy to operate.
  • The misalignment in the float installation causes it to rub against the wall of the bowl.
  • The float pin is worn out.
  • There is dirt on the needle and its seat.

Flooding is also a safety risk as any gas leaking through the throttle shaft, or vent tube can catch fire in the presence of the spark.

Adjust the Choke Control.

During cold seasons, the choke plate compensates for the cold by increasing the fuel-to-air ratio. You will usually find the choke at the throat between the air filter and the throttle plate. Closing the choke plate reduces air to the mixture, thereby enriching it to facilitate starting in extreme weather. Once the engine temperatures reach their normal value, open the choke to allow enough air for clean and efficient burning.

Ignition Issues

Next in the troubleshooting sequence is the Ignition system. Let us apprise you of the possible issues with this system that can affect the starting of the portable generators.

Is the spark plug fouled?

The spark plug electrodes must be sharp and clean, with no carbon buildup, to generate a powerful spark. A dirty or worn-out spark plug requires a higher voltage or a powerful pull on the recoil starter. Faulty spark plugs may be firing inconsistently, commonly known as the “spark miss,” resulting in poor acceleration and sluggish operation of the engine.

A damaged spark plug can cause excessive fuel consumption, oil dilution, and deposits on the cylinder head.

To remove the spark plugs, disconnect the lead and clean the area around the plug to prevent debris from falling into the combustion chamber. Use the spark plug wrench to remove and inspect the plug for the deposits. Clean these deposits with a wire brush and spray-type plug cleaner. If required, use a knife to scrape off any tough deposits.

Change the spark plug if you find burnt or broken electrodes or cracked porcelain.

Is the spark plug gap set incorrectly?

Measure the spark plug gap between the two electrodes (one curved, one straight) by a gauge. Check the owner’s manual for the recommended electrode gap. In many generators, it is around 0.030 inches. To adjust, bend the curved electrode slightly and gently and measure again with the gauge.

Is the Spark Plug, Lead, or Ignition System faulty?

Check the ignition system with a spark tester as per the below procedure.

  1. Connect the spark plug lead to the longer terminal of the spark plug tester.
  2. Connect the tester to the engine to ground it with the alligator’s clip.
  3. Crank the engine with a recoil or electric starter, and look out for spark jumping the gap in the tester. The absence of any visible spark confirms the problem with the ignition system.
  4. Test the ignition system with the ignition coil tester

Is the flywheel key damaged?

The flywheel key is fitted onto the crankshaft to engage with the flywheel. It can break due to the sudden stopping of the generator or gradually shear off.

Inspect the condition of your flywheel key for the signs of shearing. There should be no play or wobbling on placing the flywheel on the crankshaft. If you have any doubts about the condition of the key, replace it and re-torque the nut to the specified tightness. Try to restart the engine. Replace it if found effective. Else your spark plug is not functioning properly and needs replacement.

Compression Issues

If all the systems checked so far have passed the inspection, there could be issues with the compression. Let us understand them.

In a 4-stroke, are the valves, piston, cylinder, or connecting rod damaged?

Perform a compression test on a small 4-stroke portable generator engine by pulling the starter cord vigorously and simultaneously noting down the readings on the compression gauge. A value of 80 psi or more is desired. A lower value indicates poor compression necessitating a thorough inspection of valves, cylinder, and piston followed by correcting actions.

Other Issues

Some of the other issues that may be stopping you from getting your generator started are:

Low oil level sensor malfunction.

We have discussed the consequences of low oil in the section above, wherein you measured the actual level and found it to be within the required limits. However, it is also possible that the low oil sensor is malfunctioning and providing erroneous feedback.

Check if the generator is placed on an uneven surface, making the oil sensor misread the level. Otherwise, disconnect the sensor wire and try starting the generator again. If the generator starts, it is clear that the low oil sensor is faulty and requires corrective maintenance.

Dirty air filter.

Next, check the condition of the generator’s air filter. A clogged air filter will not allow adequate air in the carburetor for proper fuel and air mixing necessary for combustion. Clean or replace the air filters as necessary. Check out this video for guidance.

Cables Are Plugged into the Generator.

This may or may not actually have an impact, but it is always advisable that at the time of the generator starting, there are no cables or cords plugged unless you have a manual or automatic transfer switch installed.


While it’s impossible to cover every potential issue that could cause your generator not to start, we’ve outlined some of the most common problems. If you’re still having trouble getting your generator up and running, don’t hesitate to call a professional for assistance. With just a little troubleshooting, you should be able to get your generator back on track in no time.

Your comments about the article, any queries, or clarifications are always welcome. We will try our best to respond in the shortest time.

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