Why Does My Honda Lawn Mower Backfire?

When it comes to lawn mowers, Honda is among the most popular brands in the business. Occasionally during use, you might find that your Honda lawn mower backfires. A backfire is a pop or loud boom that occurs when gasoline ignites outside the engine’s combustion chamber; so, what causes a Honda lawn mower to backfire?

A lawn mower backfires when burning fuel enters the exhaust or the engine. This happens when pockets of unspent gasoline enter the engine or exhaust system before the valves close. Backfires occur due to rapid deceleration, faulty components, and even incorrect fuel blend, among other causes. 

Want to know more about why your Honda lawn mower is backfiring? Read on as we discuss proven ways to fix a backfiring lawn mower.  

Causes of Engine Backfires in Lawn Mowers

Below are some of the leading causes of backfiring in Honda lawn mowers.

Decelerating Too Fast

Lawn mower backfires mostly occur during rapid deceleration when the engine attempts to align its timing with the lowered throttle. In most cases, this tends to lead to excessive air in the mix, which in turn creates a lean blend. The lean blend is consequently forced into the lawn mower’s exhaust system, where it makes the infamous pop sound when it combusts. 

Slowing down a small engine should be gradual. Therefore, if your Honda lawn mower is backfiring when you’re looking to shut it off, chances are you’re decelerating too fast. The engine speed increases when using a lawn mower, and shutting it abruptly means the engine could pump some stray gas into the muffler, which could lead to combustion.

To prevent backfires when turning off your Honda lawn mower, reduce the mowing speed gradually, and allow the motor to idle for roughly 20 seconds before turning it off.

Fuel Blend

Fuel blend is a crucial aspect to consider when dealing with small engines. You’ll find that some gasoline contains ethanol or alcohol as part of the fuel blend, which can prove troublesome over time. Most Honda lawn mowers struggle to burn this blend effectively, which often results in power loss and occasional backfires.

Since lawn mowers are designed to handle specific blends of gasoline, using a wrong blend can lead to system imbalances. Due to this, it is advisable to use gas containing zero alcohol levels. If zero-alcohol blends are hard to come by, go for blends that contain low levels of alcohol.

Water Contamination

Water is another major cause of backfiring and loss of power in mowers. To remove water from your Honda lawn mower, you’ll need to start by removing the spark plug. Afterward, carefully remove the carburetor and clean it thoroughly. You should also check on the combustion chamber’s moisture levels before adding some fresh engine oil to coat the walls of the piston chamber.

Water contamination is a serious problem that, if not addressed early enough, can lead to long term damage to fuel lines, the tank, and carburetor.

Lean Carburetor

The carburetor is crucial to the functioning of a lawn mower as it regulates the volume of gas and air required for combustion. The balance must be perfect for proper combustion. While some Honda carburetors come with an electrical solenoid to control fuel flow, most come with two adjustment screws that are usually mounted on the exterior. One screw is for controlling the mix, while the other is for idle adjustments.

If the carburetor produces a lean mix, chances as the lawn mower will backfire during deceleration or even during normal operation. The good news is that carburetors are easily adjustable. However, consulting with a professional is advisable if it’s your first time attempting to adjust your Honda lawn mower’s carburetor.

Dysfunctional Valves

Valves are essential parts of a lawn mower that need to function correctly for successful outcomes. The valves help to seal off the firing chamber or cylinder of a small engine. One valve allows air and gas to make way to the cylinder while the other opens to allow the exit of exhaust gases from the cylinder.

If one of the valves malfunctions (even for a second), then the lawn mower will backfire. But fixing valves on your own isn’t recommended since they are internal parts of your Honda mower. Consider outsourcing the valve repair job to experienced service professionals.

Damaged Spark Plug

A damaged or worn out spark plug will create a weak spark that might fail to ignite the cylinder. This means that instead of igniting in the cylinder, the fuel might ignite once it reaches the exhaust muffler, which results in a backfire.

Also, an incorrectly set gap between the spark plug’s electrodes tends to result in weak sparks that make the mower unreliable. Replacing the spark is necessary if your Honda lawn mower is backfiring as a result of weak sparks.

Poor Airflow in the Engine Area

When the engine runs at a higher than normal temperature, your Honda lawn mower might gradually start to backfire. This explains why most lawn mowers require enough space in the engine housing to allow for adequate airflow.

Your engine needs enough air circulation for it to cool. Therefore, besides turning off the engine and allowing it to rest, you can consider modifying the engine’s housing to improve air circulation inside the mower.

Damage to Internal Components

Your Honda lawn mower shouldn’t backfire when starting, and if it does, then one or two components are not functioning correctly. You’ll find that a broken flywheel often leads to stuttering or backfiring when attempting to start a mower.

Luckily, the more sensitive areas of a lawn mower, such as the crankshaft, are usually surrounded by their inexpensive counterparts that cost a lot less to repair. Therefore, if your Honda lawn mower is backfiring when starting, you’ll need to call in a professional to identify and repair the damaged components.  

How to Keep Your Honda Lawn Mower From Backfiring

Avoid Cutting Wet or Damp Grass 

Mowing the lawn when the grass is wet or damp can damage your mower, consequently leading to long term problems. As mentioned earlier, you should remove water once you suspect either the tank or carburetor has been contaminated. 

Read the User Manual Before Use

Lawn mowers function differently. Take enough time to read the instructions before putting your new Honda lawn mower to good use. Generalizing the function of different brands of lawn mowers can lead to backfiring or malfunctioning when wrongly used.

Clear Debris Before Mowing

Large stones, toys, twigs, and branches might damage your Honda lawn mower. Although most mowers come with adequate safety-enhancing features, exposing them to extra hard surfaces and conditions might lead to backfiring and even total damage.

Check the Fuel Blend

Gasoline with high alcohol concentration is more likely to lead to backfiring compared to using pure gasoline. Go for fuels with little to no alcohol concentrations to eliminate the chances of backfiring due to fuel.

Final Thoughts

While it’s normal for lawn mowers to backfire every once in a while, you should always take your time to determine the cause of backfiring. Factors such as fuel blend and water contamination can gradually damage your yard-maintenance device, leading to serious defects.  

Although backfires aren’t dangerous to the engine or users, the large pop noises can be annoying. And to prevent a backfire when you’re done mowing, be sure to turn off the mower gradually, specifically 15-20 seconds after the blades have come to a halt.

Remember, since backfires tend to indicate underlying issues with your mower, you should consider reaching out to an expert if you can’t determine the cause(s) of backfires. 

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