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Lawnmower backfire when shutting off, with fixes

You are mowing your lawn, and after you are finished, you shut off your lawnmower. You observe that the lawnmower backfires and makes a surprisingly loud bang. A backfire is caused by the ignition of gasoline outside the engine’s combustion chamber. When your mower backfires, it can sound terrifying. And maybe rare, it is possible to damage both the engine and the exhaust. Usually, a backfire occurs when burning fuel enters the engine or exhaust. This fuel is in between the burning stages. Backfires can also occur when you are mowing and idle your engine.

A backfire can happen because of a mechanical problem. It usually is not a very serious issue and won’t hurt your engine. But it is something that you better fix, as it can worsen and finally damage something. Luckily it can also be fixed relatively quickly.

Why does the lawnmower backfire when shutting off:

  • 1. You do not use the correct type of Fuel
  • 2. Carburetor settings are not correct
  • 3. Spark plug is malfunctioning
  • 4. Exhaust pipes may cause some issue
  • 5. The valves are worn-out
  • 6. Solenoids may need maintenance

These problems are most fundamental. Hence, they can be solved easily by following the given points. In most cases, taking appropriate and timely steps can avoid this problem in general.

Why does my lawnmower backfire when shutting off?

A lawnmower can backfire due to several reasons. Some of the more common causes are given with some steps to solve the problem.

● 1. Backfire due to the wrong type of fuel

Some gases that contain high alcoholic blends cause the engine to backfire. The riding lawn mower cannot burn this type of fuel properly. Due to this, backfiring occurs. Suppose some amount of water is also present with the fuel; it may cause backfiring. Try to use fuel that has very low blends of alcohol. If you notice some water present, clean the fuel tank immediately. Empty the gasoline properly and add fresh fuel, which is less alcoholic. This prevents your engine from backfiring.

● 2. Backfire due to wrong Carburetor Settings

The carburetor regulates the volume of air and gas needed for proper combustion. You need to check the carburetor setting because sometimes the backfiring occurs if the carburetor is not adjusted correctly. If you don’t know how to adjust the carburetor, you should show it to the person who knows. He can adjust it for you. A carburetor consists of an electronic solenoid that controls the flow of fuel. If that solenoid is short, then it may cause backfiring.

● 3. Backfire due to faulty Spark plug

If the spark plug is damaged, then it produces a significantly less spark. The fuel may not ignite appropriately in the cylinder and might ignite when it reaches the hot muffler. Due to this, a loud backfire can occur. Check the spark plug; if it is weak, then you should replace it at once. On the other hand, if the spark plug is right, then the problem may exist in the engine or muffler.

● 4. Exhaust pipe backfire

An excessive amount of unburnt fuel remaining in the exhaust system causes the exhaust pipe to backfire. This causes the engine to backfire when it is shut off.

● 5. Backfire due to Sticky Valves

The engine consists of two valves. One valve allows the gas and air mixture to enter the cylinder, while the other valve allows releasing the gas from the cylinder after combustion. If these valves are sticky, then they might cause some issues. If they stick for a long time, the gas may pass over the muffler, resulting in a loud backfire. These valves are present inside the mower’s engine. You need to disassemble the engine to replace or repair them. In this case, you need to call a professional to check it as you cannot do it yourself.

● 6. Backfire due to a faulty Solenoids

Your lawnmower has some parts that are built in to help prevent a backfire. These are called anti after fire solenoids. These solenoids will turn the engine off at any speed and will prevent the backfires as well. You need to call a professional to replace or repair these solenoids. An inexperienced person cannot do it.

Some Preventive Measures against backfiring:

Backfiring can be prevented in many ways. If you face the same issue and your engine backfires when you shut it off, you need to follow the following measurements:

  1. Try to turn off the engine slowly. The rapid speed of the engine while shutting it off can cause a backfire.
  2. Adjust the carburetor. If your carburetor is not adjusted, it will cause backfiring.
  3. Use a suitable spark plug. If the mower’s spark plug is weak, it will produce a weak spark, as mentioned above. If this happens, replace it with a good one immediately.
  4. Replace and repair the sticky valves. Call a professional to replace the sticky valves as it cannot be done if you are not a professional.
  5. Use gases that contain soft blends of alcohol as high alcohol gases cause a backfire when you try to shut off the engine.
  6. Check the muffler construction
  7.  If the engine temperature is a bit high, try to slow down the engine speed and leave it idle for 15 seconds before shutting it off.

Types of backfires:

However, there are two types of backfires. When you shut off the engine, and the other can occur while you are shutting off your engine. The lawnmower can backfire in both ways.

1. A backfire can occur right after shutting off the engine

When you shut off the engine of the lawnmower, after that, it backfires. It may have some different reasons. This happens because of the carburetor settings. Or if there is a problem with the muffler, it can cause a backfire too. To prevent these, you need to check the muffler and the carburetor settings usually. On the other hand, if you are using different kinds of fuels, this also causes backfiring. If you are using high alcoholic gasoline, this may be the cause of the backfiring. This is because the alcoholic gas ignites the muffler instead of the engine. By using low alcoholic gasoline, you can solve this problem quite quickly.

2. Sometimes, the backfire occurs during the shut-off

This happens when you are just shutting off the engine of the lawnmower. Never slow your engine speed too fast because backfiring occurs if you slow down the engine speed very rapidly. If you are moving in the yard quickly, it increases the engine speed, and then when you shut it off suddenly, it will backfire because the engine will pump the gas into the muffler, and it could ignite there. So it would help if you were patient. Try to slow down the speed and allow the motor to idle for 15 seconds before shutting off the engine. It will prevent it from backfiring.

Frequently asked questions:

1. Does backfire damage the engine?

Yes, a backfire can not only damage the engine, but it can also damage the exhaust of your mower as well. If this happens regularly, you need to check it at once and prevent the mower from backfiring as it damages the exhaust of the mower. The fuel combustion takes place in the exhaust, which is not made to handle such high combustion temperatures. This can decrease their life.

2. Can spark plug cause backfire?

Yes, the spark plug is most likely to produce backfire. If the spark plug is damaged, it will produce a weak spark, and the fuel may not ignite appropriately in the cylinder and might ignite when it reaches the exhaust. If your spark plug is damaged, replace it at once.

If the mower’s speed is fixed as fast, the mower requires more fuel, and combustion takes faster. The spark plug can also malfunction due to this speedy combustion.

3. Can backfire cause ring damage?

When riding lawn mower is shut off, it may cause a loud backfire. This noise may alarm you, but it does not cause severe damage to the mower’s rings. However, its prolonged use in a similar condition can cause complexities.

Final Remarks:

A lawnmower is a handy machinery nowadays. People who use lawnmowers want to make their backyards more attractive and beautiful by mowing the grass in their lawns. A lawnmower is a vital machine for them. However, sometimes these machines face some trouble and issues, and they need to be treated with love and care. The above article discussed the lawnmower’s backfiring because of some mechanical problems and uncertain factors. The backfire can damage your lawn mower’s engine and exhaust, so you need to check it properly and follow the steps mentioned above to prevent your lawnmower from backfiring. In short, you should maintain your lawnmower so that it can live for extended periods. Always take care of safety precautions while repairing or troubleshooting your lawnmowers. If you face any problems in repairing, call a professional.