Why Is My Generator Sputtering/Running Rough? – [8 Reasons]

A sputtering generator isn’t only annoying but also could damage the voltage-sensitive appliances or the generator itself.

Furthermore, the Uneven or rough operation of the generator leads to reduced efficiency, power output, and important parts failure that can’t be repaired or replaced cheaply.

This guide aims to clear your burning quarries about why is my generator sputtering or running rough, how can I fix it and what should I do if my newly purchased machine is sputtering.

Why Is My Generator Sputtering? – Reasons & Fixes

1. Faulty/Clogged Carburetor:

Clogged Carburetor

The purpose of a Carburetor is to provide a balanced air-to-fuel mixture to the combustion chamber for proper combustion so that the generator can run smoothly.

If the Carburetor is bad or clogged, the combustion chamber will not get proper air to fuel mixture and as a result, the generator starts sputtering/running rough.

Stall or low-quality fuel is the most common reason behind clogging the generator’s carburetor; however excessive dirt/sediment could also be a reason.

NOTE: Don’t ever leave the fuel inside the generator’s carburetor/fuel tank for a longer time, it turns stall by absorbing moisture from the air or may leave the sticky material once the fuel is evaporated.

  • Solution: Clean The Carburetor.

Clean the carburetor and inspect its jets, fuel lines, etc, after a deep clean-up, replace it and start the generator.

If the problem is still there the carburetor may need repairing or replacement in worst cases.

2. Clogged or Broken Fuel Lines:

Broken fuel lines

Clogged or broken fuel Lines running from the generator’s fuel tank to the carburetor restrict the flow of fuel and as a result, the generator starts sputtering.

  • Solution: Inspect and Replace the Broken Fuel Lines.

Carefully inspect the conditions of the fuel lines, and also make sure to clean them inside, If you find something broken, make sure to replace them. I mostly use a compressed air can to clean the insides of the fuel lines.

3. Low Quality or Stall Fuel:

Stall or bad quality fuel that sits for more than 3 months without any stabilizer, loses the power of combustibility because of the excessive moisture content.

In case your generator is fed with stall/bad quality fuel, the symptoms will be sputtering, rough running, shaking, low or fluctuating voltage, etc.

  • Solution: Drain the Stall Fuel.
  • If you suspect that your machine is fed with the stall fuel make sure to drain the old fuel from both the carburetor and fuel tank, Also pour some high-octane fresh fuel or at least a normal fuel with a fuel stabilizer.
  • If you are storing the fuel in a can or any container, make sure to airtight it and Stick a piece of duct tape on it with the date. Don’t use more than 3 months old fuel.

NOTE: The fuel stabilizer should be poured directly into the generator fuel tank to ensure a proper mixture of stabilizer and fuel should be fed to the combustion chamber.

Recommended Read: Why Is My Generator Shaking?

4. Dirty or Clogged Fuel Filter:

The purpose of a fuel filter is to ensure that dirt and debris-free fuel should be transported to the carburetor.

Over time the small pores that hold the dirt become clogged and restrict the flow of fuel to the carburetor causing the generator to run rough.

  • Solution: Clean or Replace the Fuel Filter.

Remove the fuel line running from the fuel filter to the carburetor and turn on the fuel valve, if you find insufficient fuel is coming from the fuel line then the fuel filter is the culprit.

Remove the fuel filter and clean it with the gasoline and rag recommended by the manufacturers. If the fuel filter is in extremely bad condition make sure to get another one. Here is the guide about Replacing or cleaning the generator’s fuel filter.

5. Clogged Air Filter:

Clogged air filter

Like the fuel filter, the air filter also blocks the dirt and debris entering the generator’s carburetor to ensure a cleaner intake of airflow should be available for proper combustion or cooling down the engine.

If the air filter is choked/clogged the generator will misfire or sputter as there will be no air for building a proper air-to-fuel mixture for the combustion.

  • Solution: Clean or Replace the Air Filter

Read the user manual and remove the air filter from the air filter’s housing, clean it carefully with a mixture of soup and pressurized water (if needed), and pour some engine oil on the surface.

If you find damaged or cracked foam, make sure to replace it.

Recommended Read: Easy steps to clean the generator’s air filter

6. Faulty Spark Plug:

Faulty or bad spark plug

A spark plug is the only organ to ignite the air and fuel mixture available in the combustion chamber for generating the required power.

If it malfunctions, there will be no proper combustion, and as a result, the generator will not start or run rough.

  • Solution: Replace the Bad Spark Plug

Remove the spark plug and inspect it, if you find it fouled with a damaged electrode or covered with carbon deposits, replace or clean it.

Recommended Read: How to clean or replace the spark plug of a generator?

7. Overloading:

Overloading occurs when the generator needs to draw more power than its capacity.

If you have pulled more load than the generator’s rated/surge watts the generator becomes overloaded causing rapid breaker tripping, overheating, sputtering, excessive wear and tears, etc.

  • Solution: Disconnect the Appliances and Reset the Generator.

Disconnect all appliances reset the generator’s breakers, adjust the load, and find the reason behind overloading.

We recommend following our comprehensive guide about identifying and fixing an overload generator.

8. Fuel with Excessive Ethanol:

Though EPA, ADFC, and other environmental firms encourage to use an ethanol rich fuel to reduce the emission of carbon dioxide, still it has a pretty low shelf life with hygroscopic properties.

The normal amount of ethanol in the fuel wouldn’t be a problem however excessive amounts may reduce the burning efficiency, Also it should be properly treated otherwise the gasoline and water may be separated.

  • Solution: Drain the Old Fuel and Flush the Fuel System if Needed.

Drain the old gasoline and wash the fuel lines, fuel tank, and carburetor of the generator, pour high-octane fuel, and operate the generator for a while.

Recommended Read: Generator revs up and down.

Why is My Newly Purchased Generator Sputtering?

If a newly purchased machine is sputtering, your first take is to replace it unless you have operated the generator with a stall or ethanol-rich low-quality fuel.  

Modern fuels are mostly treated with ethanol, a combination of MTBE and alcohol to reduce the environmental impact; however, they significantly lose their shelf life and can’t be used if they sit for more than 30 days.

If you have poured a high octane fresh fuel and still the generator is sputtering the most obvious reasons could be a faulty factory-fitted carburetor or fuel lines that restrict the air or fuel flow causing improper air to fuel mixture.

Additionally, the AVR, capacitor, and spark plug could also be culprits, still, they aren’t that expensive and could be replaced within no time.

Humble Suggestion: If your newly purchased generator is sputtering, don’t do the DIY hacks unless you are 100% sure about what you are doing. Get a replacement or Claim your money.

Why Is My Generator Sputtering/Not Running Smoothly Without Load?

As I have mentioned above the clogged filters (fuel and air), carburetor, faulty spark plug, overloading, etc. are the main reasons your generator is running rough.

However if you have done the above fixes and still the problem is there, you should inspect the below things.

  • Look for the choke position; it should be at run.
  • If you own a dual-fuel machine, the fuel selector may be malfunctioning. As per my experience, a bad fuel selector could mix the propane and gasoline and as a result, the combustion chamber is not getting enough energy to move pistons evenly. If this is the case with you seek help for a generator’s mechanic.
  • Inspect the governor spring if it’s loose or disconnected make sure to reconnect it.

How Do I Make My Generator Run Smoother?

  • Make a proper Schedule of maintenance; keep the carburetor, filters, spark plug, and fuel lines cleaned.
  • Use fresh high-octane or normal fuel with a stabilizer if possible.
  • Don’t let the generator sit for too long without running the engine, keep operating it periodically to prevent excessive build-up or stall fuel.
  • Drain the gasoline from the generator’s carburetor and fuel tank if the generator needs to sit for more than 4 months.
  • If the generator isn’t operated for a month, use a fuel stabilizer before firing it up. Pour the stabilizer into the generator’s fuel tank and run for about 10 minutes, so that the stabilizer can mixed properly.
  • Avoid overloading the generator.
  • Inspect the choke, fuel valves, and a few necessary things, and make sure they should be at the right settings.

Final Words

Fortunately, Sputtering of the generator isn’t a major problem and can be fixed cheaply by cleaning the generator’s vital organs like carburetor, filter (air and fuel), spark plugs, etc., unless there is a major fault like faulty carburetor, fuel lines, rotor faults, etc.

If your newly purchased generator is running rough/sputtering, we recommend to claim your money back

I hope you are now able to fix a sputtering generator without hiring a mechanic, if you are still confused, let me know in the comment section I will be more than happy to assist you!

Frequently Asked Questions – FAQs

What Causes a Generator Not to Run Smoothly?

Clogged filters (fuel and air) and the contaminated carburetor is the major cause of the generator not running smoothly, however, stalled fuel and a faulty spark plug could also be the reason.

Make sure to follow this section of the article and apply the fixes we have listed If the problem is still there, seek help from a professional generator mechanic.

Is It Normal for a Generator to Shake?

No, if a generator is shaking heavily for no reason the engine mounts may wear down or the engine is misaligned.

For a newly purchased generator we recommend claiming its warranty; however, for an old generator, you should consult with a generator mechanic for better assistance as per the situation.



Kashif has been a valuable asset to the electric generator industry for over 5 years. Now, As a skilled energy engineer, he’s been on the front lines of diagnosing problems, fixing broken parts, and performing routine maintenance tasks to keep generators running smoothly.

Leave a Reply

Your email address will not be published. Required fields are marked *