Backfire is the loud bang or explosion that your lawnmower may produce while running or shutting off. This sudden surprise can be irritating and you may end up wondering why does my lawn mower backfire. Although backfire does not damage your engine, it can be an indicator of some other hidden mechanical issues that should be addressed. Read on to discover the causes and solutions to your lawnmower backfire.
When does a backfire occur?
While starting the lawnmower
It is very unusual for a lawnmower to backfire while starting. However, if it occurs, it can be an indicator that the mower’s system is damaged in some way. It may be because the mower hit a hard obstruction the last time you were mowing and it damaged the flywheel. If the flywheel is damaged, the mower may stutter and backfire while starting. The mower would not work until you fix this issue. If a mower backfires while starting, it is advised to seek professional help instead of trying DIYs.
While shutting down
If your mower backfires while shutting down it may be because you are slowing down the speed too fast. It leads to the fuel being pumped in the muffler where ignition takes place resulting in a backfire. A backfire while shutting down can also be due to the overheating of the engine. Backfiring mostly occurs at this step.
After shut down
There can be several reasons behind your lawn mower backfiring after shutting down. It may be due to incorrect carburetor settings, the quality/type of the gasoline being used, and the construction of the muffler. These points will be further discussed in detail.
What Causes Backfiring?
Some of the possible causes of why your lawn mower backfires are:
Fuel Mix
The gasoline you use may have some part of ethanol or alcohol as a blend. The engine of some lawn mowers such as riding mowers is unable to burn such gasoline properly. It may lead to occasional backfires. Prefer using pure gasoline to avoid backfiring and power loss. Another reason can be the water contaminating the fuel. If you sense this, empty the tank of gasoline, dispose that off and add fresh fuel to the tank.
Carburetor Adjustments
A carburetor works to regulate the ratio of air and gas needed for proper combustion. An imbalance in the ratio can lead to improper combustion or even no combustion at all. A lean carburetor mixes too much air with too little fuel. This can lead to backfiring.
There are two adjustment screws on the carburetor. One is for idle adjustments while the other screw controls the mixing of gas and air. It is preferable to seek professional services in order to make carburetor adjustments however, if performed carefully, you can make the adjustments yourself. just make sure that while turning the screw you make small increments and keep testing the mower. Some brands of lawnmowers have an electronic solenoid that regulates the mixing of oil and gas. Any issue with the solenoid can also result in backfiring.
This guy shows how to adjust the carburetor in two minutes. Watch and learn.
Spark Plug and poor ignition
If the spark plug of the mower is damaged or has an improper gap between the electrodes, a weak spark is generated. In this case, the fuel would not ignite in the cylinder and would rather ignite on reaching the muffler which results in a backfire. A lawn mower with a damaged spark plug would run unreliably and may break down any moment during the mowing. If the spark plug is the cause, replace it and then test the mower.
Lowering Engine Speed
Sometimes the mower backfires during shutting down because you are slowing down the speed at a faster speed. While you are mowing, the engine picks a faster pace and if you try to slow it down quickly, it would pump the gas into the mower’s muffler. The gas may ignite in the muffler causing a backfire.
To remedy this, make sure that you decrease the speed gradually and let it sit idle for at least 10 minutes before turning off the mower.
Motor Timings
The timing of engine processes is very crucial for smooth functioning. If your mower is backfiring, check the timing of the motor. If the motor is set at the wrong timing, the fuel may ignite while the valves are still open causing a rapid backfire. Even if you set the right timing in the first place, after prolonged use, the timing between the valve and the engine can be disturbed and needs to be readjusted.
Sticky Valves
The two valves of the engine serve the purpose of sealing and firing. One of the valves is responsible for letting the gas and air mixture into the combustion chamber. The other valve opens and allows the exhaust gases to leave the combustion chamber. If the valves are sticky and take longer to close, the gas mixture can escape the chamber and enter the muffler. There are chances that the gas may ignite in the muffler causing backfire and power loss.
As valves are an internal component of the engine, it is not possible to repair them at home. The repair or replacement of the valves requires the tearing down of the engine and it is best to leave this task to the professionals.
How Do I Avoid Backfiring?
To avoid backfiring, make sure you take the following measures while operating a lawn mower:
- Lower the speed of the engine slowly so that the fuel is not pumped into the muffler
- Use pure gasoline with no blends of ethanol or alcohol
- Do not set the carburetor adjustment lean
- Let the engine cool down before turning off the mower
- Regularly examine the carburetor, engine, and fuel lines.
- Look for any holes, loose screws, rust, or metal fatigue that may affect the performance of the mower.
Anti-Backfire Device
If you have tried everything and still have to get scared of the loud bang every time you operate your mower, consider installing a piece of anti-backfire equipment into your mower. An anti-backfire solenoid immediately blocks the flow of fuel at the carburetor once the ignition switch is turned off. This keeps the fuel from getting anywhere else such as into the muffler and causing a backfire. It is also called as an anti-after fire solenoid as it stops the bang/spark that may occur once the mower is being turned off.
You would need professional help to install an anti-backfire solenoid as it can be tricky.
Frequently Asked Questions
What does it mean when a lawn mower backfires?
A backfire is a loud bang or explosion that may occur while you are turning the mower on or off. It happens if any fuel is spread to any other component of the engine except for the carburetor and the combustion chamber. When the ignition takes place at a place that is not designed for combustion, the mower produces a loud bang.
Does backfire damages the engine?
Though backfire does not directly damage your engine, it is an indicator of an underlying issue in the engine that needs to be addressed. It leads to power loss and a lot of fuel is wasted as a result.
Concluding Note
Engine backfires can be scary and irritating sometimes. This article has covered all the possible causes of the backfire along with the fixes. Just make sure that not every engine-related issue can be fixed by you at your home. Some issues need professional help to be fixed, if otherwise, they may lead to may injury or serious damage to the machinery.