Why Is My Generator Backfiring? (Fixing Guide)

A generator is a super helpful machine that can be used in various situations. When there is a power outage or during emergencies, a generator can save the day by providing backup power. Since you don’t use it regularly, sometimes it may fail to start or backfire due to being in an idle state for an extended period. This brings us to the main question, why is my generator backfiring?

The most common cause of a generator backfiring is a poor fuel-to-air ratio in the engine. However, there are several other reasons as to why your generator would backfire, including a bad spark plug, low oil, open choke valve, clogged or damaged fuel line, closed fuel valve, clogged carburetor, etc.

Like any other engine, a generator needs frequent servicing and maintenance to ensure it stays in good shape and can normally start whenever you need to use it. This article explores why a generator backfires, causes of backfiring, and how to fix a generator backfire. Keep reading to find out more.

Why Is My Generator Backfiring?

As aforementioned, a generator backfire happens when the air and fuel mixture combusts outside the combustion chambers. This is caused by an imbalance of fuel and air, making it impossible to ignite. Usually, your generator will produce a sputter or loud pop sound but won’t start. Depending on your generator, smoke or flame may shoot out from the exhaust when backfiring; this can cause damage to your generator.

Why Is My Generator Backfiring

If your generator has been sitting for several weeks or months, it may fail to start normally. It is advisable to regularly check and run your generator for at least five minutes to avoid such problems. There are several causes of generator backfiring; below are a few most commonly reported causes and how to fix them:

1. Bad Spark Plug

A spark plug is an essential component of your generator. It creates the spark which ignites the compressed fuel to start the engine. Sometimes, there could be a build-up of debris and soot, preventing the plug from igniting. This leads to timing issues and generator backfiring. A good clean or replacing the spark plug solves this problem.

bad spark plug

2. Closed Fuel Valve

The fuel valve controls the fuel line that lets out fuel from the fuel tank to the combustion chambers. A closed fuel valve cuts the fuel supply necessary for starting your generator. As the generator engine tries to start with little fuel, it produces a pop sound and backfires.

Closed Fuel Valve

3. Low Oil

Any machine with an engine requires oil to reduce friction. To get the best and maximum performance of your generator, consider using good-quality and clean oil. When refilling your generator oil, make sure you put it on level ground so that you don’t underfill or overfill.

If your generator backfires while starting, check its oil level. The low oil level will prevent your generator from starting. Gritty and dark oil means you need to replace the oil.

4. Open Choke Valve

The choke valve regulates the amount of air going into the generator before turning on the engine. Should your generator choke valve be open, the combustion chamber won’t get sufficient fuel to ignite and start the engine; this causes your generator to backfire.

You should close the choke valve completely before starting your generator, then steadily open the valve while the engine is running. Again, if you keep the choke valve closed, your generator will trip.

5. Damaged or Clogged Fuel Line

As explained in the closed fuel valve above, a clogged fuel line blocks the fuel supply. Blockage can occur from accumulated debris from the fuel tank. Damage such as leaking cracks can be due to exposure to harsh conditions or normal wear and tear. A damaged fuel line needs to be replaced immediately, while blockages need to be thoroughly cleaned by flushing the fuel line and tank.

6. Clogged Carburetor

Storing your generator for a prolonged period with fuel in it can cause the carburetor to clog. While most manufacturers recommend running a generator once a month, others recommend once in a week. Running your generator once in a while is better and easier than emptying its gas tank. It also reduces the chances of your generator backfiring.

Clogged Carburetor

7. Poor Fuel-to-Air Ratio

An improper fuel-to-air ratio causes slow combustion. When slow combustion occurs and the exhaust valve is still closed, it causes a valve overlap, and your generator will backfire.

Generators that are used regularly, such as a generator for mobile detailing, have minimal chances of backfiring. While those sit idle for prolonged periods, such as backup power generators, tend to backfire or trip when you start the engine. Frequent running of your generator engine can reduce the chances of backfiring.

Can A Backfire Cause Generator Damage?

When your generator backfires, you need to find the cause. Backfires can cause generator damage, decreased fuel efficiency, and power loss if left unattended. Some generator backfires can travel up to the intake valve, while others shoot out through the exhaust, causing an “after fire.” Visible fire and smoke can be produced at the tailpipe of the exhaust.

How Do You Fix A Generator Backfire?

Since there are several causes of generator backfiring, the right approach is to fix the particular cause of backfiring. For example, if your generator backfires because of a bad spark plug, you need to clean or replace it.

However, some other causes of generator backfiring may require detailed servicing or repair, especially if it has been sitting for a long time.


Normally, running a generator engine should burn fuel and produce electricity. However, when your generator has not been in use for a long time, it might not function as intended. This shouldn’t worry you. If you have read through this article, we hope you understand why your generator backfires and some probable causes.

If you experience generator backfiring problems, you should resolve the issue immediately to avoid damaging your generator. Always refer to the manufacturer’s manual or consult a certified generator technician if you run into serious problems. Remember to observe the basic generator safety measures.

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