Lawnmower shuts off when blades are engaged. This is how you fix it.


On a clear day, you take your lawnmower out in the garden to give the grass a nice, fine trim. However, you become upset about seeing the engine shut off whenever the blade engagement lever is pulled. Your mowing session comes to a halt, and you aren’t sure how to fix this. You’re wondering whether it can be resolved by yourself or you need to take it to a mechanic. There can be multiple reasons for the mower shutting off with the blade engagement. To diagnose the problem, we have to check these, one by one.

Lawnmower shuts off when blades are engaged. This is how you fix it:

  • Step 1. Check the blades of the lawnmower.
  • Step 2. Check the quality of the engine oil.
  • Step 3. Examine the spark plug of the lawnmower.
  • Step 4. Clean the dirt from the carburetor.
  • Step 5. Check the level of engine oil in the oil tank.

Before we understand the causes of a mower shutting down, it is important to understand the process behind it. The engine receives an air-fuel mixture from the carburetor. It undergoes combustion to produce power. If the air-fuel mixture isn’t supplied in an adequate amount, possibly due to restrictions in filters, jets, or due to insufficient fuel, the power delivery gets minimized. Hence, when we add load on the engine by engaging the blades, it dies down due to its insufficient power.

To understand the various troubleshooting steps involved, we will look at the causes and fixes in more detail.

Diagnose the lawnmower shuts off when blades are engaged:

Use the following steps to diagnose and fix the problem that your lawnmower shuts off when you engage the blades.

Step 1: Check the blades of the lawnmower

The lawnmower’s blades may be damaged after being used for a long time or hit a solid object. The worn-out blades will get less effective in cutting the excessive grass properly. The blades may get entangled with the long grass. The entangled grass will put more strain on the engine and eventually shut the lawnmower down. If your engine just has enough power to deal with this type of grass, this can be the cause of the problem. If your engine has more than enough power, it is less likely that this is the cause. Replace worn-out or bent blades, or if still possible, sharpen them.

  • Step 1: Tip the mower over. Firstly, you need to tip the lawnmower at the side opposite the carburetor. It prevents any leakage of the fuel during the procedure.
  • Step 2: Check the blades. Check the blades, and if they are indeed in bad condition, continue removing them.
  • Step 3: Remove the blade. The fasteners holding the lawnmower’s blades should be removed using a wrench. Now, the lawnmower’s blades can be removed. Use gloves before handling the blades if they are still sharp.
  • Step 4: Sharpen the blades. If the condition of the blade is still good enough to sharpen them, use a file or grinder to do this. Check the blade balance, and if needed, adjust it.
  • Step 5: Install the new blade. If you install a new blade, ensure that it is the correct type. Attach the new or sharpened blade on the mower, and check if it has fixed the problem.

Step 2: Check and clean the carburetor

The carburetor is the place where the engine oil and oxygen are mixed. The carburetor provides a slow and continuous mixing of oil and air. If the carburetor is dirty, there won’t be sufficient space for mixing. It may lead to shutting down the lawnmower if more power is asked from the engine. Also, starting the lawnmower will be more challenging. The solution is to clean the carburetor.

Remove the carburetor, and use some carburetor cleaner. If you do not have that, you can also use WD-40. Leave the carburetor cleaner for some time so it can do its work. Wipe it off using a cloth and clean it thoroughly. Ensure that you clean the screw-hole as well. Reattach the carburetor bowl back and screw it using a screwdriver.

Step 3: Clean the air filter

The air filter removes dirt and other particles from the air before it goes into the carburetor. Gas needs enough oxygen to burn efficiently. If dirt is accumulated in the filter, there is less space for the air to go through it. This results in a less optimal burn and an engine with less power. When you ask for more power when you engage the blades, it will shut down.

The air filter of your lawnmower should be cleaned or replaced if damaged. The filter’s wing net should be removed first, followed by removing the top half of the filter. If your lawnmower uses a foam filter, first remove the visible dirt. Then use some water and soap to clean it fully, and let it dry. If the filter looks bad or is damaged, replace it. If your mower uses a paper filter, you need to replace it. Put the filter back in its place. If it is all okay, tighten the wing net over it.

Step 4. Examine the spark plug of the lawnmower

If your lawnmower’s spark plug is not working correctly, it can cause misfiring in the engine and does not ignite the gas-air mix properly. The mower will often be challenging to start and shuts down after interacting with the grass. Remove the spark plugs and check them. Suppose they are dirty clean them. Use a feeler gauge to check the gap distance, and adjust if needed. If the spark plug looks bad, replace it.

Step 5. Check the level and quality of the engine oil

Oil is vital for a lawnmower’s smooth operation. If you use low-quality engine oil or it is older and dirty, this can disrupt your engine’s smoothness. The absence of enough oil in the engine may cause wear and tear, damage the engine, or render it useless if left untreated. The quality of the oil should be considered while buying the engine oil. If you have low-quality or old oil in your oil tank, drain the oil from the mower.

Add new fresh oil, and make sure you do not overfill it. Check with the dipstick that the level is fine. If the oil looks fine, check the level. And add oil if needed.

Precautionary Measures:

Whenever you are dealing with machines, it is better to take some precautionary measures before working or maintaining them:

  • Disconnect the spark plug cables: When you work on or near moving parts, first disconnect the spark plug cables. This ensures that no unintentional engine start can occur.
  • Cooldown: Make sure that the lawnmower is cooled down before operating it.
  • Sharp blades: The blades should be handled with care. It is advised to wear a pair of gloves before the blades are treated.
  • Oil spillage: While pouring in the oil, there should be no spillage of oil over the lawnmower’s body. The reason for doing this is that the oil makes the body greasy, and it may also drip off while mowing.
  • Cover after removing: When you remove the filter, cover the engine so that no dirt enters it.
  • First aid kit: Always keep the first aid kit with you while repairing the lawnmower.

Frequently Asked Questions:

1. What to do If the blades break off during un-bending them?

If the blades of the lawnmower get bent while mowing the lawn, they can be brought back to their original shape by using pliers or a vice. If they break during this process, there is only one option, replacing them.

2. What is the easiest way to check the oil level in your lawnmower?

The best way to check the oil level is to use the dipstick. It should be in the oil tank, or part of the oil cap. Take it out, and clean it. Put it in again, remove it and check the level. There should be a marking for the correct level (often a range). If needed, add some oil.

Engine oil is used and consumed whenever you mow your lawn. You might notice that after several mowing sessions, the level is lower. When your lawnmower gets older, this often goes faster.

3. The air filter is broken. What to do?

If you notice that the air filter is broken while cleaning it, you have to replace it. The best is to fit a replacement before continuing using the lawnmower. But if you do not have the replacement immediately, and the damage is not that great, you could use the cleaned and damaged air filter one more time. You can only do this if the filter can still do its job. If you notice that unfiltered air can enter the carburetor, you should not do it. Try to replace it as soon as possible.

Final Remarks:

Technological devices like lawnmowers are although simple to use, yet sometimes need some maintenance. If they are not maintained time-to-time, they may cause issues later on. It could also affect its operation. It is better to regularly inspect the lawnmower even if it is working smoothly after some months, so it does not break down the time you need it. All the steps mentioned above may help you fix your lawnmower so it does not shut down when it gets engaged. But if the engine’s problem persists, it is better to take your lawnmower to your nearest mechanic for its fixing.

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