Nothing in yard work is more frustrating than needing minor lawn mower repair. Many times, we have brought out the old lawn mower for the first mow of the new season with great anticipation. With the perfect spring day, we are all set to give the lawn the attention it needs after a long winter. You pull the cord over and over and over and get nothing but sore arms and frustrated. In most cases, it was probably something minor, but you couldn’t track down the problem and give up in frustration. You grab your car keys and head out for the lawn mower repair shop. Or, more likely, you go to the nearest garden center to buy a newer, more reliable mower.
In many cases, that purchase may not be necessary. Most gasoline-powered lawn mowers, especially those that have sat idle for months, develop starting and running issues that can be easily corrected if you know what to check for. In this tutorial, we’ll show you the most common problems lawn mowers can develop. We’ll also show you what to do about them without dropping a lot of money.
Before You Begin to Troubleshoot
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Before you do anything else, disconnect the spark plug wire. (The spark plug wire will tend to bend back toward the plug and may even touch it, so be careful.) Completely cover the wire connection with a piece of electrical tape and try to move it as far from the spark plug as possible.
Set the throttle all the way to hit the “stop” position.
Wear work gloves
Work gloves prevent cuts and scrapes from sharp edges on various parts of the engine. Engines can be very dirty and grimy. So, even a small cut from a sharp edge in this environment can become infected.
Wear eye protection
Eye protection will prevent accidentally getting gasoline or small metal shards in your eyes.
Check the gas
If your mower has been sitting for months, and you didn’t drain the gas prior to storage, empty the gas tank completely and refill it with fresh gas. Be sure to dispose of the old gasoline in accordance with your local environmental laws and regulations. (Your local auto parts store or shop will usually dispose of it for you.) You should do this before you try to start it, whether you suspect issues or not. Heat, oxygen, and humidity can alter the fuel’s delicate mixture of hydrocarbons and cause it to be less likely to function in your small mower engine.
Additionally, most gasoline sold in the US contains a percentage of ethanol. Ethanol tends to absorb water vapor from the air and mix it with your gas. If you have water in your gas tank, your engine becomes susceptible to everything from fouled plugs to a seized-up engine in extreme cases. In either case, the small amount of gas you will dispose of is still less expensive than the problems it can cause.
Clean the air filter
Finally, remove the air filter and clean or replace it. Some filters require a different cleaning and preparation regimen than others. If you have a sponge-type filter, remove the air filter cover and the filter. Clean with compressed air or rinse with cleaner, diesel fuel or gasoline. Squeeze it until your cleaning fluid no longer drips out. Then, allow the filter to dry. Recheck the filter before replacing it. Reattach the cover. If you have a paper filter, simply discard and replace it. Again, the possible problems it can cause by deterioration and collected dirt are not worth the minor price of replacement.
If after all these preventative steps, you try to start your mower and it either fails to start, runs roughly, or stalls, we will begin the troubleshooting procedure. These steps are not intended to correct major mechanical or fuel system issues. They are meant to solve the most often occurring minor problems that prevent the proper operation of your lawn mower engine. These are issues that you can correct yourself with just a little time and effort.
Now that we are ready to start troubleshooting let’s check the most likely things first.
Check the Spark Plug and the Spark Plug Wire
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Before checking the spark plug, visually inspect the spark plug wire for cracks or frayed areas. Also, ensure that the connector fits tightly on the spark plug.
The spark plug itself could be defective or incorrectly gapped. Check to see if it is getting a spark. You can do this in one of two ways.
Either make sure the plug wire connection is less than 1/2-inch away but not connected to the spark plug terminal and try to start the engine. If your system is working correctly, there should be a visible spark jumping from the wire to the spark plug. When doing this, remember to always respect the mower and treat it as if it could start any time
The other method of checking the plug involves removing it, reconnecting the wire, and carefully grounding the bottom of the spark gap to see if there is a spark in that gap. While this method is a bit more controllable, the spark in the plug gap area arcs over a smaller area, which makes it more difficult to see.
If you do not see a spark and have used the first method, now remove the plug. Visually check it to look for physical damage such as cracks in the insulator or damage to the gap arm on the bottom of the plug. If it shows any damage at all, replace it. They are not expensive and can be dangerous if damaged or defective.
If they look intact and undamaged, the plug may simply be gapped incorrectly. Check the gap for the spark plug in your owner’s manual. If you no longer have one, you can usually look it up online. Find the appropriate gap for your mower engine and check it against the gap in the spark plug with a gapping tool. There are several inexpensive gap tools available. Either the wire or the blade type gap tool works equally well.
Re-gap the spark plug if necessary. Replace the spark plug, reconnect the wire, set the throttle to “start,” and try to start the mower again. If it still will not start, move to the next check.
Checking and Cleaning the Carburetor
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Second only to a spark plug issue, the carburetor will be the likely cause of the engine failing to start, running roughly, or stalling. Remove the air filter and inspect the carburetor. Just because it looks clean on the outside may not mean that it’s not dirty or restricted on the inside. The carburetor has to be clean to function properly. If your mower has been sitting idle for months, the carburetor may require a thorough cleaning before it will cooperate. You can use regular automotive carburetor cleaner to accomplish this.
Give the carburetor a few quick, short squirts directly down the throat of the device. Be sure to avoid spraying plastic parts if you can. Reassemble and try to start the mower. If it still does not start, proceed to the next check.
Check the Fuel Tank Cap
If the engine still has trouble running and has a gas tank with a vent hole, the hole may have become clogged. A clogged hole can cause a vacuum to form in the gas tank as the fuel level goes down. That will slow or stop the fuel flow and stop your engine. You can check to see if this is the issue by slightly unscrewing the cap just enough to allow a minute amount of air to enter the tank. To clear the hole, you can stick a small wire or jeweler’s screwdriver through the hole.
If your mower has a rubber push primer button, check it to ensure that the button contains no cuts, deterioration, or holes. If the push primer is defective, replacing it requires no special skills or special tools. You can find instructions detailed step by step for your particular mower online. The replacement button costs about $5.
Other Lawn Mower Repair Issues
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Occasionally, your mower may stop or run roughly for reasons completely unrelated to the mower itself. Some of the other common issues that can hinder your lawn mowing could be simpler to correct than you think.
If the starter rope is hard to pull
On some mowers, the safety bar that must be held down to allow the mower to run may not be open far enough to allow you to pull the rope. Make sure the safety bar is completely tight against the handle.
The rope may also be hard to pull because the mower is in tall grass that is stopping the blade from rotating freely. Just move your mower to a paved or bare area and try again.
If your mower has wet grass caked under it, you may also have trouble pulling the rope. Never try to clear the underside of your mower unless the mower is off and the spark plug is disconnected. Turn the mower over and remove the grass with a broom, stick, or another long object. Never use your hands, even if you think it is safe!
If you lose power while mowing
Losing power while mowing could be the result of tall or very thick grass. In this case, try cutting this area after raising the height of your blade. Then, go over the same lawn area again with the blade a bit lower until you reach the correct cutting height.
As with the previous issue of the rope being hard to pull, having a buildup of debris under your mower can also cause it to sputter and stall. Clean it away as described above.
If your engine is smoking
Your lawn mower’s engine will smoke for several reasons. If the oil level is too high, or if you dripped some oil on the exhaust muffler while filling it, the problem isn’t severe. Allowing the mower to run until the excess oil burns off will usually solve the problem. However, if there is smoke coming out of your exhaust muffler, and your mower runs roughly or constantly stalls, you may have an issue that can’t be fixed by DIY means.
My New Lawn Mower Won’t Start!
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Sometimes we bring home a brand-new lawn mower, put the gas and oil in it, try to start it up, and nothing happens. We try it again, and still nothing. Before you drive it back to where you purchased it to demand a refund or exchange, there are a few things you can check.
Prime the engine
A new mower that has never had gasoline in it will have air in the fuel lines and the combustion chamber. For that reason, you will need to prime the pump. Usually, in newer mowers, it is a simple case of pressing the rubber primer button a time or two. The manual on your new mower will tell you how many times the manufacturer suggests you push the primer for perfect starting.
Remove the old fuel
Occasionally a retailer will put fuel in the mower to test it or for some other reason. A mower fueled by the retailer beforehand may have been sitting for some time. In this case, the gas may have gone bad. Empty the tank (as described earlier) and fill it with fresh gasoline.
Is it a two-stroke engine?
If your shiny new mower has a two-stroke engine, you have to mix oil with the gas before filling the tank. A four-stroke mower needs only regular gasoline. However, a two-stroke engine requires a very special mixture of gas and oil that you can find in your owner’s manual. With too much or too little oil in the mixture, your engine might not start or run properly.
Check the choke
An engine with a carburetor may have a choke shipped in the closed position. This choke restricts the amount of air going into the carburetor. Increasing the airflow will cause the fuel to temporarily burn hotter and faster. This will help start the engine. After it starts running, close the choke back to the normal operating position.
Is there a “safety switch”?
Check your engine for a cutoff switch. Newer gasoline mowers come with a switch that cuts off the fuel flow to prevent leakage. Also, check to see if your new mower incorporates an electric cutoff switch. Electrical cutoff switches are sometimes installed on mowers with electric starters to prevent accidental and unwanted starts.
Having Tried All These Lawn Mower Repair Measures
If none of these fixes resolves the problem, and your mower still doesn’t start or run properly, it may be time to consider repair or replacement. In the case of a brand-new mower, call the dealer or the manufacturer’s helpline to see if they have any recommendations before making the trip. Hopefully, these inexpensive measures will save you the cost of a repair or buying a new mower, or an unnecessary trip in the case of a new one. They have saved me money countless times when faced with a reluctant lawn mower, and I hope they will do the same for you.