Generator Backfire: How to fix it?

Generator Backfire How to fix it
Table of Contents
    Add a header to begin generating the table of contents

    Do you hear a loud popping sound when you try to start the generator? The popping sound is generator backfire; it can be as loud as a balloon explosion or a gunshot. Depending on the state of the generator, flames or smoke may also shoot out of the exhaust when it backfires.

    Loud noises can scare your neighbors into calling 911 or even damage your generator. If you’re wondering why your generator backfires and won’t start(12 Common Reasons Why Your Generator Won’t Start), the team of experts at BISON generator has some answers here.

    Check generator spark plugs

    Common causes and solutions

    1. Low oil

    Your gas generator needs oil, just like a car, to lessen friction inside the engine. Fill your generator with clean, high-quality oil and place the machine on a flat surface for the best results. However, avoid over-oiling the generator, as this could impair its functionality.

    If your generator backfires when trying to start, check the dipstick. If the oil turns black and gritty after a few months of use, this could be the reason why your generator is backfiring or failing to start. A low oil level will also prevent the generator from starting.

    2. Old or dirty fuel

    If the generator backfires, another reason could be that the fuel in the tank may be old or dirty. Leaving fuel in the tank for months can cause it to degrade. Degraded or stale fuel is not flammable. Fuel flammability also decreases when mixed with water, oil, or other contaminants.

    If gasoline is not burning the way it should, it can negatively affect the combustion system’s performance and can backfire. Avoid such problems by sucking old or dirty fuel from the generator and replacing it with fresh fuel.

    3. Open the choke valve

    Your generator has a choke valve that stops the intake air before starting the engine. If the valve is open, the generator’s internal combustion engine won’t get enough fuel to fire, causing backfire, and the engine won’t start.

    Before turning on the generator, close the choke; once it has started to run, open it. If the choke is closed after starting the generator, the unit will not run smoothly and may eventually stall.

    4. Close the fuel valve

    The fuel valve controls the fuel lines that deliver gas from the fuel tank to the combustion system. If you close the fuel line, your generator won’t be able to start and run since it won’t have access to gas. When the engine tries to run with its little gas, it sputters and backfires.

    5. Blocked or damaged fuel lines

    A closed fuel valve is one of many things that can prevent your generator from getting enough gas. A clogged, pinched, or leaking fuel line can also cause insufficient gas to reach the combustion system.

    Blockages can occur due to debris in the fuel tank accumulating in the fuel lines. Leaky cracks in fuel lines may be due to years of exposure to these elements.

    You must replace the leaking fuel line, but you can fix the blockage by simply flushing the tank and fuel line.

    6. Carburetor clogged

    Some generator manuals recommend running the generator at least monthly, while others recommend running it weekly. If you don’t run a fuel generator for months, the fuel will clog the carburetor.

    As we mentioned earlier, the fuel remaining in the tank will gradually degrade and become non-flammable. If this fuel gets into the carburettor, it clogs it and prevents fresh combustible fuel from getting in. When the engine tries to ignite the degraded fuel, it can backfire.

    Prevent such problems by emptying the fuel tank before storing the generator. You must use the generator at least once every month if you decide to leave the fuel in it.

    It is preferable to run a generator each month as opposed to draining its gas tank. This is because running a generator allows you to verify that the system is working well and that you can rely on it to supply power during a power outage.

    7. Lean fuel-to-air ratio

    If your generator has a leaner fuel-air ratio, it will cause slow combustion. During slow combustion, the combustion process cannot keep up with the mixing of air and fuel in the combustion chamber. When this happens, the exhaust valve doesn’t open, causing valve overlap and the generator to backfire.

    The lean air condition of your generator can be caused by a dirty, old, or improperly adjusted carburettor.

    8. The spark plug is damaged

    Spark plugs help with the ignition needed to start an internal combustion engine. It starts the engine by generating a spark to ignite the compressed fuel. Over time, spark plugs can wear out and become dirty. When this happens, the combustion system won’t get the spark it needs, causing timing problems and generator backfire. If your spark plug is causing the generator to backfire, replace it.

    How to prevent generator backfire?

    There are a number of things you can do to prevent generator backfires. The most important thing is to make sure the fuel mixture is correct, and the carburetor is clean and adjusted correctly. You can also try using higher octane fuel in your generator.

    You should also check the exhaust system for leaks and ensure the clips are tight. Ensure the generator is properly fueled and doesn’t fill up the tank. Finally, make sure the spark plugs are in good condition, and the ignition is working properly.

    Why does the generator backfire when shutting down?

    Some generators backfire when you turn them off. But it’s a minor problem that you can easily fix.

    Often the generator backfires when you turn it off, especially if it’s running at high RPM. What happens is that when the generator is off, the piston still has residual motion. The momentum will cause the air-fuel mixture in the combustion chamber to ignite, creating a popping sound spontaneously.

    You can fix this by putting the generator in idle mode for a while before shutting it down.

    Note that in this case, there is no spark when the generator is off. As a result, the air-fuel mixture entering the combustion chamber is not ignited. Therefore, it will pass through the unburned exhaust chamber. The supply of fresh air in the exhaust may cause spontaneous combustion, causing a backfire.

    The degree of backfire will depend on the heat in the exhaust chamber. It’s usually not too loud because the residual momentum isn’t as high as the normal operation of the piston. You may also see some sparks, but they shouldn’t scare you as the problem is usually harmless.

    How to prevent a backfire when shutting down the generator?

    You can prevent your generator from backfiring by not suddenly shutting down the generator’s engine. Instead, switch all the devices running on it and leave it on for a while before shutting down. A one-minute span is sufficient to allow adequate readjustment of the fuel supply to the combustion system.

    Your generator can also backfire when you shut it down due to fuel additives and the use of contaminated fuel. Also, avoid ethanol blends as they interfere with the function of the combustion system. The use of fuel stabilizers is still acceptable. Nonetheless, you must make sure to stay within the recommended amount.


    Keeping your generator in good condition is crucial because it doesn’t let you down when you need it most. So the key imperative to make sure it’s in good condition is to understand why it’s backfiring.

    There are several reasons for this problem. However, it would help if you distinguished between backfire and after firing as they are two distinct but related issues. After firing is not that much serious. But a backfiring problem needs to be solved quickly.

    BISON generates manufacturer has discussed with you how to fix the backfiring issue in this guide. The most important thing is to make sure you take the advice and take the necessary precautions we’ve discussed.

    Generator Backfire FAQ

    We can't tell directly whether a backfire will damage the generator's engine, as it depends on several factors.

    This is a big problem if your generator produces afterfires, especially if it's loud. Problems like this can affect the functionality of your generator. It will struggle to function properly, which will cause wear and tear in the long run. The worst-case scenario is when afterfires are too loud. In this case, the exhaust system will be damaged after a while.

    If it's not loud, you can ignore the afterfire. If the afterfire is too loud, you need to fix it. Remember that backfire occurs when combustion occurs in a carburettor with a fuel reserve. Therefore, you need to fix the backfire as soon as it is diagnosed, as it will blow up the combustion system.

    If your generator bursts suddenly during normal operation, it means there is a considerable problem with the combustion system. Usually, pops can be caused by a poor air-fuel mixture. It could also be that some part of the combustion system is malfunctioning.

    Sometimes, popping isn't a huge problem. But it would be best if you didn't ignore it because it can exacerbate huge challenges. The best remedy is to have a mechanic check for possible causes of the burst. It should be easy to detect as most popular problems revolve around oil burning.

    The most common causes of a generator backfire are carburettor problems, bad spark plugs, and exhaust problems.

    you may also like

    Home large petrol electric generator

    5KW 220V 50Hz petrol generator


    1000w portable silent gas inverter generator

    Small quiet 650w gasoline generator

    12kva air cooled diesel power generator

    If you have any enquiries about the BISON generator, we would love to hear from you.

    Send Your Inquiry Today Now

    contact us now! get the latest quote for generators.
    I will reply within 24 hours.