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generator backfire: causes and fix

While generator backfires can occur unexpectedly, it is almost always a symptom of an underlying problem in the generator system.

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In everyday life, even an indispensable piece of equipment like a generator is subject to malfunctions and deviations. One of the most worrisome and potentially dangerous is a phenomenon known as “generator backfiring.”

When you try to start your generator, this sudden ignition of unburned fuel in the exhaust system can cause a deafening shock, and more importantly, it can cause significant damage to your generator, raise serious safety concerns, and render it inoperable when you need it.

Understanding generator backfiring: its causes and fix. It is critical to the use and safety of your generator. This article is an important guide to help you safely deal with the potential threat of generator backfires. Stay tuned to China BISON and arm yourself with the knowledge you need to keep your generator running efficiently, safely, and permanently.

generator backfire

common causes of generator backfire

While generator backfires can occur unexpectedly, it is almost always a symptom of an underlying problem in the generator system. Here are 9 key factors that contribute to this phenomenon:

low oil

Oiling your generator not only helps with friction but also helps cool various engine components. However, be careful not to over-oil the generator as this may reduce its efficiency.

If your generator backfires when trying to start, check the dipstick. If the oil level is low, it can cause overheating(Generator overheating causes and solutions), causing the generator to backfire.

old or dirty fuel

Fuel degradation or contamination can lead to poor combustion, which might result in the fuel igniting at an unintended location within the generator.

When the generator fuel remains stagnant over an extended period, the molecular structure of the fuel may undergo damage, leading to an imbalance in the fuel-air ratio and subsequent backfiring.

In instances where the fuel becomes contaminated or mixes with water or other impurities, the fuel-to-air ratio is disrupted, causing suboptimal engine performance and, in severe cases, backfiring.

To prevent backfiring and ensure optimal unit operation, consistently utilize fresh, high-quality fuel. Consider changing the gasoline every 3-6 months for improved performance.

open throttle valve

Your generator has a choke valve that blocks air intake before starting the engine. If the valve is open, the generator’s internal combustion engine will not get enough fuel to ignite, causing backfire and the engine will not start.

closed fuel valve

The fuel valve controls the fuel line that carries gas from the fuel tank to the combustion system. A fuel valve that closes means the engine is not getting enough fuel and can also lead to a lean condition that can lead to a counterproductive situation.

blocked or damaged fuel pipeline

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.

generator backfires carburetor clogged

blocked carburetor

If you don’t run a fuel-fired generator for several months, fuel will clog the carburetor.

As we mentioned before, fuel left in the tank will gradually degrade and become non-flammable. If this fuel gets into the carburetor, it will clog the carburetor and prevent new combustible fuel from entering. When the engine tries to ignite the degraded fuel, it can backfire.

Emptying the fuel tank before storing the generator can prevent such problems. If you decide to leave fuel in the generator, you must use the generator at least once a month.

lean air-fuel ratio

An imbalance in the air-fuel mixture, particularly lean conditions, could lead to incomplete combustion, with excess fuel being expelled into the exhaust and possibly ignited there, causing backfire.

Your generator’s lean fuel-to-air condition may be because of a dirty, old, or improperly adjusted carburetor.

broken spark plug

The spark plug initiates combustion. Over time, spark plugs wear out and become dirty. This can cause the fuel to ignite at the wrong time or not ignite at all, resulting in residual fuel in the exhaust system that can ultimately lead to backfiring.

premature/early combustion

If the ignition timing is off, and combustion happens too early, it could cause a backfire. This can happen due to electrical faults, mechanical faults, or a malfunctioning ignition system.

how to fix generator backfiring

how to fix generator backfiring

To address generator backfiring, start by pinpointing the underlying cause, likely one of the previously mentioned issues. Additionally, assess whether the backfiring occurs when transitioning from higher RPM to lower RPM upon shutdown, as it might not necessitate immediate repairs.

However, if your generator exhibits backfiring during startup or while running, it likely requires repair.

The following steps will guide you in resolving generator backfiring:

carburetor and spark plug:

  • If the problem persists, the air-fuel mixture ratio is incorrect. In this case, clean the carburetor thoroughly. A faulty spark plug may also be a cause.
  • Proper cleaning can solve about 80% of generator backfiring problems. If the generator will not be used for an extended period, you should consider draining the carburetor.


When backfiring occurs during startup, focus on the valve. Possible issues include a decompressed spring, improper clearance between the valve stem and pushrods, or a bent rocker arm. Several complications may arise from the valve face in the combustion chamber.

backfire during shutdown:

If backfiring occurs when turning off the generator, follow these steps:

Disconnect all loads and operate the generator in ECO-MODE or idle mode for a few minutes. This approach reduces the likelihood of backfiring by promoting normal combustion.


Generator backfire is not only an operational problem, but it also presents a safety risk. In addition to mechanical damage, backfires and resulting small explosions can also start larger fires, especially if the generator is located near flammable materials.

BISON talks to you about how to solve counterproductive problems in this guide. The most important thing is to make sure you follow the advice we’ve discussed and take the necessary precautions.

We think you’ll find this guide useful! Thank you for taking the time to read, and remember to check out our related articles for other valuable tips on generator repair.

generator backfire FAQS

To prevent generator backfire, the generator should be maintained regularly, keep the fuel fresh, clean or replace the air filter, check and replace spark plugs as needed, check the exhaust system for damage or blockage, and adjust the carburetor appropriately.

If your generator produces embers, it can be ignored if it's not loud. If the residual fire is too large, it may affect the function of the generator. It will struggle to function properly, which will lead to wear and tear in the long run. The worst thing that can happen is that the ember is too large. In this case, the exhaust system will become damaged after some time.

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