Why won't my lawnmower start? Do this
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Most of the time, a lawnmower that is hard to start or runs rough does so because the gas is bad or the carburetor is dirty.
How to Get a Lawnmower to Start Again
1) Replace the Bad Gas in your lawn mower
Why won’t my lawnmower start? Do this
When a lawnmower won’t start, especially after being stored, it’s almost always because the gas is bad.
If you don’t add gasoline stabilizer to the fuel tank before putting away your lawnmower in the fall, the fuel can break down and clog the fuel lines. We explain here how to fix a lawnmower that won’t start if that doesn’t work.
Over time (like the six months your lawnmower sat in your garage over the winter), the lighter hydrocarbons in gas can evaporate. This process creates gums and varnish that dirty the carburetor, plug fuel passages and prevent gas from flowing into the combustion chamber.
The carburetor bowl below formed corrosion and deposits during storage, which can easily plug fuel passages and prevent the engine from starting.
If you don’t stabilize the gas in a lawnmower before putting it away for the winter, deposits can build up in the carburetor and make it so dirty that the lawnmower won’t start in the spring. Sometimes all that needs to be done to fix the problem is to change the gas.
2) Is there a problem with the gas in your lawnmower? Here’s How to Repair It
Ethanol-containing gas can absorb water from the atmosphere, causing phase separation, which occurs when ethanol and gas separate in the same way that oil and water do. Ethanol that has absorbed enough moisture and sat for an extended period of time can clog the fuel system and prevent the engine from starting.
If the lawnmower is trying to run on bad gas, no matter how many times you yank the pull cord and pollute the air with your upset language, it will not start.
In extreme cases, the evaporation of lighter hydrocarbons can alter the composition of gasoline enough to prevent it from igniting. It doesn’t matter if the gas is fueling the engine if it won’t ignite.
If you forgot to add gasoline stabilizer to the fuel before storing it, empty the tank and replace it with new gas. If the tank is nearly empty, simply topping it off with fresh gas will often get it started.
The fuel tank on some mowers can be easily removed and emptied. That is sometimes more trouble than it is worth. To remove the bad gas in these cases, use a fluid extraction pump or even a turkey baster. You don’t have to get rid of everything, but try to get as much out as possible.
Spray carburetor cleaner into the intake after removing the air filter. Allow it to sit for a few minutes to loosen deposits.
This type of “quick-and-dirty” carburetor cleaning is usually all that is required to get the gas flowing again and your lawnmower cutting grass again.
If not, remove the carburetor from the engine, disassemble it, and clean it thoroughly. But be warned: for the uninitiated, disassembling a carburetor can lead to nothing but frustration. Take photos with your phone to help with reassembly. Take note of any linkage positions or mixture screw settings, if applicable. If you are hesitant, go to the servicing dealer instead.
Move the compressed air from the inside of the air filter outwards to clear out any debris that might be stopping the lawnmower from starting because it isn’t getting enough air.
3) Clean/Replace the Air Filter in your lawn mower
On some carburetors, the float bowl is easy to take off. If it has one, first take out the small drain plug and let the gas out of the bowl, if it has one. Take off the cover of the float bowl and spray carburetor cleaner on the float and the small fuel passages.
Now that the air filter is out of the lawn mower , it’s a good time to clean it.
To get grass clippings, leaves, and other debris out of rigid filters, tap them on a workbench or the palm of your hand. Move the compressed air from the inside of the filter to the outside so that dirt doesn’t get further into the media.
To clean foam filters, use soap and water. If it’s been a few years, just replace the filter. They’re cheap and the only thing stopping debris from getting into your engine and wearing down the piston rings and cylinder walls.
If the gap between the spark plug and the engine isn’t right, the engine won’t start. Follow the instructions in the owner’s manual to set the gap.
4) Check the spark plug on your lawn mower
It could also be a dirty or broken spark plug. Pull the plug out and look at the condition. If a four-stroke engine is running well, the spark plug should last for years and never look oily or burned. If so, get rid of it.
Check for spark with a spark-plug tester. If you don’t have one, clip the spark-plug boot to the plug, hold the plug against the metal cylinder head, and slowly pull the starter cord. You should see a blue spark that is strong. It’s best to test the plug in a garage where it’s dark. If you don’t see a spark or it seems weak, you should change the plug.
While you’re at it, check the spark plug gap and set it to what the lawnmower’s owner’s manual says it should be.
If the plug is good and you still don’t have spark, it’s likely that the coil has failed and needs to be replaced.
In this case, if your lawnmower won’t start, it’s likely because you broke the flywheel key. It’s a small piece of metal that puts the flywheel in the right place to set the right timing for the engine. If you hit an immovable object, the mower blade (and crankshaft) will stop right away, but the flywheel will keep turning, shearing the key.
In the event that, the engine timing is off, the mower won’t start until the flywheel is removed and the key is put back in. If you have a set of gear pullers in your garage, it’s an easy job. If you don’t have a set, you can rent one from a parts store, buy one (because there’s never a bad time to buy a new tool), or go to the dealer.
My lawnmower starts, but it doesn't run well.
If you finally get the lawnmower to start, but it runs like a not so tamed lion, try using AMSOIL Power Foam to clean the carburetor. It is a powerful cleaner made to get rid of carbon, varnish, and other gunk that slows down engines and carburetors.
Add Gasoline Stabilizer to Avoid Most of These Problems
Which makes more sense? When your lawnmower won’t start, do you do all of these steps every year? Or putting a little stabilizer in your gas tank?
Most problems with a lawnmower that won’t start can be solved by adding a good stabilizer to the gas.
For example, AMSOIL Gasoline Stabilizer keeps gas fresh for up to a year. It keeps the lighter hydrocarbons from evaporating, which keeps gum and varnish from forming and keeps the fuel moving. It also has chemicals that keep the metal from rusting.
In my garage I have a five-gallon gas container I use to fuel two lawnmowers, two chainsaws, two snowblowers, a string trimmer, and an ATV. Every time I put gas in the them, I use Gasoline Stabilizer to keep the gas from going bad and causing problems.
AMSOIL Quickshot is another tool you can use. Its main purpose is to clean carburetors and combustion chambers, but it also fixes problems caused by ethanol. But it also keeps gas prices stable for up to six months in the short term.
Use good oil in your lawnmower's engine.
Even though motor oil has nothing to do with whether or not your lawnmower starts (unless you don’t use any oil and the engine seizes), it’s still a good idea to put good motor oil in your lawnmower.
This is especially true for people who use expensive zero-turn or riding mowers for work or at home.
Oil doesn’t last as long in lawnmower engines as most people think. They are usually cooled by air, which means they run hotter than car engines that are cooled by liquid.
Often, they have to run for hours in hot, dirty, and wet weather. Many don’t have an oil filter, which puts the oil under even more stress.
Standard motor oils can break down in these situations, leaving behind harmful deposits and giving less protection against wear.
Use a commercial-grade motor oil like AMSOIL Synthetic Small-Engine Oil in your lawnmower to get the best performance and longest life.
Its long-life formula has shown over and over again that it can safely go longer than the OEM (original equipment manufacturer) drain intervals, even in the worst conditions. It gives extra protection when equipment goes longer than the OEM recommends between oil changes.
Matt Marciniak, the owner of Duluth Lawn Care, says, “If it’s not broken, don’t fix it.” Since he has always used AMSOIL products, he spends more time using his mowers, trimmers, and other tools and less time fixing them. Listen to his story.
