Why Generator Won’t Start Just Backfires?

Why Generator Won’t Start Just Backfires? 9 Possible Reasons

Do you see flames or smoke when you turn on your generator? Do you hear loud pops? A backfire has a similar sound to a gunshot or a balloon popping.

Here’s a single question that has come up: Why Generator Won’t Start Just Backfires?

If your generator backfires and won’t start, it has likely been idle for some time. It can be necessary to replace old fluids, broken fuel lines, or spark plugs. Check the oil and gasoline levels, as well as the valve settings.

Why Does My Generator Backfire?

Generator combustion is slow due to lean fuel-to-air ratios. Mixing air and fuel in the combustion chamber cannot keep up with the combustion process when combustion is slow. The generator backfires when the exhaust valve is closed due to the valve overlap. 

What Distinguishes Between A Generator Backfire And Afterfire?

There is a difference between “backfire,” which describes pops or flames coming from the carburetor, and “afterfire,” which happens when your exhaust emits a pop or flame through the exhaust itself.

Potential Causes of Backfiring in Your Generator

Limited Air And Fuel Mixture In The Carburetor

Effective combustion requires a sufficient amount of air to occur. Insufficient air will cause the fuel to burn more slowly. You’ll frequently find that power is still ignited even when business is slow. It will take longer than usual to consume one unit of energy because of the slow speed.

As a result, combustion will continue after the power stroke is over. So, when the piston of the generator rises during the exhaust stroke, it will stop the burning process.

Does anything happen at this time that affects the generator in any way? It would help if you were ideally prepared for this to occur during the exhaust stroke since the exhaust valve opens initially. Additionally, the intake valve allows fuel and fresh air to enter the combustion chamber. Be aware that the initial mixture of gasoline and air is still burning. When the flame of the slowly burning fuel ignites the newly arriving mixture, an unexpected pop sound will be made. It could also be attached to a flame that would backfire. 

Air jets should be examined as the first defense against this issue. They are most likely not providing enough air to the combustion chambers. Additionally, a gasket leak might exist at the junction connecting the combustion chamber and the air filter. Any air that enters so exhales before burning entirely. 

Another possible cause of the issue is that your carburetor may be loose. That would allow air to escape through the sides, preventing effective combustion. Not to mention, it’s also possible that your generator uses subpar fuel. The bulk of a generator’s combustion problems starts in the carburetor. You should therefore handle this component with caution.

Limited Air And Fuel Mixture In The Carburetor
Why Generator Won't Start Just Backfires? 9 Possible Reasons 1

Initial Fuel Combustion 

A backfire could happen if the carburetor burns fuel too quickly. It starts with a spark that ignites earlier than usual. 

The piston typically pulls downward during the intake stroke to help the air-fuel mixture enter the combustion chamber. Once there is enough fuel and air in the system, the piston starts to rise. At this point, the intake valve ought to be closed. 

However, the valve does not permanently close on schedule. If this occurs and the spark plug ignites, the mixture of air and fuel will burn on the combustion plug. Because the piston will also be carrying air and burning fuel to the carburetor, a backfire will follow.  A variety of factors can cause the timing error. The flywheel key may be a problem, a damaged spark plug, or an ignition coil malfunctioning and starting the engine when it shouldn’t.

Intake Valve Blocked

Backfire can happen through the carburetor if the intake valve opens and shuts to admit fresh air-fuel combination from the carburetor into the combustion chamber in the open position when it shouldn’t be. 

This might be due to a misaligned rocker arm area, an incorrect clearance between the valve stem and the pushrod/rocker/tappet, or a decompressed spring on an overhead valve variation due to one of the clips falling off. Another possibility is a rusted valve. 

In all of these scenarios, the exhaust or the burned air-fuel combination will shoot back into the carburetor if the intake valve is open or cracked when it shouldn’t. If the valve opens, it will undoubtedly blast back into the carburetor. However, it could also blow back via the exhaust. 

You need to remove the valve cover and check the rocker arm/tappet area to see any issues with your valves. Ensure all the springs are compressed, the clearances are proper, and nothing is bent or broken. Pull the recoil starter cord carefully, take out the spark plug, and watch the rocker arms and valves in action. Check to see if any of the valves are stuck. 

You might need to remove the combustion chamber head to find more problems, such as a cracked valve face or excessive carbon buildup between the face and the seat. As a result, it wouldn’t close correctly, allowing exhaust gases to reenter the carburetor.

Intake Valve Blocked
Why Generator Won't Start Just Backfires? 9 Possible Reasons 2

Other Root Causes of Backfiring or Non-Starting Generators

Less Oil

You might not see oil when you disconnect the pipe since the tank could be empty, which would account for the situation. If you attempt to start it with inadequate gas, it will fail. Your generator’s engine needs oil to reduce friction. For the best performance, refuel your generator with pure, high-quality oil and place it on a level surface.

Low Or Outdated Fuel 

Old and dirty fuel tends to become less combustible than brand-new fuel. It burns more slowly. If the fuel is not burning correctly, combustion will not perform as well as it should.

While you’re there, check the gasoline level. There could be a gasoline shortage in the tank. When their fuel is running low, generators frequently malfunction.

Problem With A Clogged Valve

Your generator needs the proper balance of oxygen and fuel to function correctly. That’s why it features a choke valve, which allows you to control how much air enters the engine. When attempting to start your generator, this should be closed. If left open, the engine will get too much air and not enough gas. Instead of a smooth start, you’ll only hear a handful of sputtering pops.

If your engine is backfiring or won’t start, it’s possible that the choke has been left open and the engine isn’t getting enough gas to ignite correctly.

Fuel Valve Is Closed

Your generator needs the fuel valve to be open to start instead of a closed choke valve. The valve may occasionally be closed when a generator is stored between uses. When you try to start the engine, the gasoline will not flow properly if the valve is still closed. If not, you’re stopping the flow of fuel. Whatever gas remains in the cylinders will attempt to be used by the engine. There won’t be enough to start the motor, just enough to create a bang.

Fuel Valve Is Closed
Why Generator Won't Start Just Backfires? 9 Possible Reasons 3

Clogged Carburetor

For a while, refrain from using the generator since the old gasoline may block the carburetor. Because the air and fuel mixture in the combustion chamber is wrong, the debrief makes it hard for the new fuel to be injected properly. This leads to incomplete combustion.

Before putting your generator away, empty your drain carburetor to prevent blockage. Find the drain, and let any old gasoline flow into the bucket. In more challenging situations, you might need to remove the entire bowl and clear away any leftover debris. You can try starting the generator again with new fuel after removing the older fuel. If you want to store the generator for a long time in the future, you may be able to avoid this problem by either draining the gas tank after the last use or turning the generator on and running it often to let fresh fuel flow through.

A Faulty Spark Plug

A combustion engine requires a spark plug to generate the spark that ignites the compressed gasoline and launches the engine. Like the gasoline line, the plug frequently develops junk buildup, impairing its performance. A good cleaning will often fix the problem, but sometimes it needs to be replaced.

During starting of an internal combustion engine, the choke valve inhibits airflow; hence, it must be closed when starting a generator. Limiting airflow causes the machine to be inundated with more gasoline, making starting it much more straightforward. The choke should be opened once the engine begins to ensure the best performance. It’s possible that the choke was left open, which stops the engine from getting enough gas to form, causing it to backfire or not start.

A Faulty Spark Plug
Why Generator Won't Start Just Backfires? 9 Possible Reasons 4

What Leads To Afterfire In Generators? 

Backfire and afterfire sound the same to some people. Generator combustion system problems cause both. If you can’t tell them apart, you can’t pinpoint the source of the pop sound. 

Air-Fuel Mixture Shortage 

You could also encounter an afterfire due to the delayed burning of fuel, similar to a backfire. The burning rate is sluggish when there is a problem with the combustion system. So, during the compression phase, the mixture of air and fuel already burning can go back to the carburetor and cause a backfire.

At the same time, most burning air-fuel combinations may be expelled during the exhaust stroke. The end consequence will be a pop sound and the discharge of flames from the generator’s exhaust. The noise indicates unusual combustion.  Similar to a backfire, such an event is known as an afterfire. Similar to a backfire, although it occurs in the exhaust rather than the carburetor.

Air-fuel Mixture Oversupply 

An abundance of an air-fuel combination can occasionally cause an afterfire. If there isn’t enough air getting into the combustion chambers, some of the fuel may not be wholly burned.

Similar to the situation discussed before, during the exhaust phase, unburned fuel is forced into the exhaust chambers. The unburned fuel will ignite quickly when it comes into contact with the abundant oxygen in the exhaust chambers. Additionally, observe how warm the exhaust chamber is in this scenario. 

The gasoline will ignite as a result of the encounter and make a loud pop. The amount of unburned gasoline that hits the air will determine how loud the pop will be.

Combustion Delay 

Early combustion can generate a backfire, as mentioned above. An exhaust afterfire can be created by a delay in chamber combustion can create an exhaust afterfire. In delayed combustion, an afterfire occurs after piston compression. This procedure may hinder the spark plug’s ignition spark release. The air-fuel combination burns late in the process. 

Instead of burning in the preceding phase, it’ll burn in the exhaust. The piston expels a burning air-fuel combination, not burned gases, during compression. An oxygen-rich exhaust chamber ignites the mixture. The exhaust fold is extremely hot. Therefore, quick burning will make a pop sound. 

The spark plug may be causing the wrong timing. Sometimes it may malfunction and spark. Shear in the flywheel key affects spark release. Last, check the ignition coil. 

An Issue With The Exhaust Valve 

In the event of a backfire, we clarified that a problem with the input valve might be a contributing factor. Similar to how a valve issue may result in an afterfire, it’s an exhaust valve issue this time. 

On the seat of the exhaust valve, carbon can build up occasionally. The valve won’t completely seal the space as a result. As a result, there won’t be a proper seal, allowing the unburned air-fuel combination to enter the exhaust chamber. The mixture ignites quickly in the scenarios mentioned earlier and produces a loud pop sound. 

The amount of air-fuel combination that enters the exhaust chamber will determine how loud the pop will be. The problem can be resolved by reducing the carbon buildup in the seal region.

An Issue With The Exhaust Valve 
Why Generator Won't Start Just Backfires? 9 Possible Reasons 5


Frequently, there is a straightforward fix for a generator that is backfiring and won’t start. The engine will need to be emptied and replaced if the oil and gasoline are low or deteriorated and hinder a proper start. Similarly, dirty fuel lines or malfunctioning spark plugs will prevent correct fuel flow and need to be changed.
Check the oil and fuel levels as well as the choke and fuel valve positions before trying to start your generator. For the machine to start, the choke must be closed and the fuel valve must be opened.


  • Can A Backfire Or Afterfire Harm The Engine Of A Generator?

    A backfire may or may not affect a generator’s engine.
    Afterfires may be noisy and dangerous. It may affect your generator’s performance. It won’t work properly, creating wear over time. The worst is afterfire. The exhaust will fail.
    A quiet afterfire may be ignored, but a backfire must be dealt with. Burning carburetor fuel reserve causes a backfire. Backfires may destroy the combustion system, so fix them right away.

  • Why Is There a Popping Noise Coming From Your Generator?

    Your generator’s combustion mechanism is broken if it pops while running normally. A poor air-fuel mix might cause pop noises. Some parts of the combustion system can be damaged. Not all popping is detrimental. If left unattended, it can worsen a serious issue. A mechanic should look at the cause of the pop. It should be evident as oil combustion is a common cause of public worry.

  • When You Turn Off Your generator, Why Does It Backfire?

    A generator often backfires when you turn it off, particularly if it is spinning quickly. The piston continues to move after the generator stops, which is what occurs. The air-fuel combination will spontaneously burn in the combustion chambers due to the motion, producing a popping sound.

  • How Can Backfire Be Avoided When Turning Off a Generator?

    Prevent a backfire by not suddenly switching off the generator. Please turn off all its appliances and let it sit before closing it off. A minute is enough to adjust fuel to the combustion system.

  • Popping Generator: What Does That Mean?

    Is your generator chattering or popping? A bad fuel mix or failing part is likely. A fuel mix issue creates a “sputtering” sound, while a component failure sounds like metal on metal. Spotty generator output.

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