You’re all set to make quick work of your lawn only to find out that your lawnmower starts then dies right away. We can understand the frustration while you scratch your head thinking about what could possibly be wrong.
Firstly, if it starts at all, that means spark and compression are present. It is likely a fuel issue such as a dirty carburetor, but it might also be due to clogged air filter, blocked gas line or a flywheel issue.
Don’t worry; it’s very common that your lawnmower starts but won’t stay running. Often, emptying the gas tank and cleaning the carburetor and orifices will fix the mower. But there can also be other reasons, and it’s best to get it fixed as early as you can.
Let’s look at some of the common reasons why your lawnmower starts but then dies, and how to fix each one of them.
Main Causes and Solutions For “Lawn Mower starts then stops”
If you have not been diligent about your mower’s maintenance, the problem is likely with a gummed or clogged carburetor. It may sound complex, but you don’t always have to visit a repair shop whenever that happens. We’ll help you identify the problems and potential fixes you can try to save on repair bills.
1. Dirty Carburetor
Your lawnmower’s engine present in Husqvarna Z254, HU700H etc. is equipped with a carburetor that’s responsible for mixing air and fuel in the proper ratio for combustion. This combustion, in turn, runs the engine by continually rotating the crankshaft. If the carburetor is gunked or loose, it won’t be able to maintain a steady supply of gasoline for the engine’s proper functioning.
Fixing this is easier than it may seem. Before you proceed, always check if the carb is fixed firmly so that it can maintain sufficient gas flow. Once you’ve ensured that, it would need a good cleaning using a carb cleaner. The carburetor cleaner usually comes in an aerosol can and is dirt cheap, but if you want to make the job easier, get one with a jet spray.
Simply drop the carburetor bowl by unscrewing it and clean the bowl, screw and the orifice with the carb cleaner. Once you’ve given it a nice spray, put everything back together firmly but not over-tightening the screw. The plug shouldn’t be pushed if it meets some resistance and you should be able to thread in with your fingers. It’s possible that a few threads or seals might get stripped during the process; in that case, you may need to replace those seals.
Also, don’t put the air filter yet. First check whether the engine starts without that and if it does, put the air filter and try to start. If the lawnmower starts but then dies, it’s time to clean or change the air filter. If it still doesn’t get it fixed, you’re possibly looking at a faulty carburetor or one of the other causes mentioned below.
2. Gas Gone Bad (Formed Residues)
Gas usually turns bad after 30 days, and if the gas in your mower has been left out for a while, the volatile components get evaporated leaving behind a greasy residue. This residue will block the gas line and other parts restricting gas flow due to which your lawn mower won’t stay running.
Completely drain out the gas from the gas tank, you can also try running the engine to clear out as much gas from the carburetor. Once you have it completely out of gas, put in fresh gasoline along with the fuel stabilizer. Fuel stabilizer is good to have as it can prevent residue formation for a longer time, but it won’t help the engine combat the effects of time.
Fuel stabilizer is inexpensive and is an excellent investment to enhance the longevity of your mower. Just make sure that you get the fuel to stabilizer proportion right by referring to the owner’s manual for your mower. Alternatively, you can choose to add new gas to the existing fuel to dilute the residue, but we would suggest adding fresh fuel.
3. Defective Spark Plugs
A spark plug is what ignites the combustion by supplying electric current to air-fuel mixture. Depending on the spark plug’s age or the amount of wear, it might need to be replaced or in some cases, can be cleaned and get it running.
If you have an old spark plug that seems to be heavily degraded with carbon build-up, you need to replace it. Replacing it is easy and inexpensive, and all you need to take care of is the right size. On the other hand, if it doesn’t seem to be heavily coated with dirt or carbon deposit, you can simply clean and wipe it up using a wire brush and any good cleaner.
Ideally, spark plugs need to be changed every season. You can do this as a part of your annual maintenance routine plus add new oil and air filters at the same time. This would enable your mower and the engine to work for a long time without giving you much problem.
To replace the spark plug on your mower, you need an old plug with a properly sized socket wrench. For the new plug, you need to adjust the gap between the two electrodes at the top to the recommended size as per the mower’s manual. Afterwards, you can install the new spark plug and attach the lead. Just tighten it up enough and stop as soon as you feel some resistance.
4. Too Much Oil in The Reservoir
If you’ve checked and cleaned the carburetor, gas tank and the spark plug but your lawnmower still keeps dying, you possibly have too much oil in the oil reservoir. A superficial sign that can help identify this is when there’s smoke coming out of the engine. This will cause the engine to eventually stall as a result of feeding on too much oil.
Another way to determine this is by tilting the lawnmower itself for some time so that the oil finds its way to other parts. Let it sit like that for a while and then try running the engine. If it runs for a good amount of time without stalling, you know the culprit is excess oil. Once you find that out, it’s easy to fix, and you need to drain the excess oil. You can do that either with the help of a siphon or by tipping the mower and let the oil drain from the hole.
You can use a dipstick to check the oil level and release or add until you reach the full level. Put the mower back up and start the mower again. If the smoke is gone and the engine stays running, you’ve fixed the mower. It’s not uncommon to overfill the oil tank, and users tend to go overboard while doing it themselves. But there’s no need to panic if you find it out early enough.
Other Causes Of “Lawn Mower Won’t Stay Running”
Besides the reasons mentioned above, there can be some other minor and some more serious issues why your lawnmower keeps dying. However, if you don’t feel comfortable trying everything discussed here, it’s always a wise decision to hire a professional or visit a service shop. Having said that, let’s take a look at other reasons why your self-propelled or riding mower starts then dies.
1. Clogged Carburetor Bowl
Most carburetors in an internal combustion engine are equipped with a bowl, which is nothing but a mini fuel tank mounted on the carb that regulates fuel flow. These bowls are supported by a screw that goes into a hole underneath the carburetor.
This hole might get clogged up, which will keep the gas from moving freely to and from the bowl. To clean the bowl, you need to remove it using an appropriate plug wrench and then clean the bowl and the hole for the screw. You can use carb cleaner for the bowl and screw, and a thin wire for the hole.
2. Blocked Gasoline Cap
It’s possible that the holes in the gasoline cap get clogged which will destabilize the air pressure in the gas tank. These holes are responsible for maintaining the air pressure so that gas can move freely into the carburetor.
You can try cleaning these holes with a thin wire. If you see that the cap is worn out or falling apart, then replace it and get a new one.
3. Worn Out Carburetor
Whether you live in a temperate region where your mower is needed year-around, or in northern areas where it has to sit for the entire winter, the carburetor will always need a little kindness and attention. Especially if it’s an old mower which has undergone several repairs, the carburetor will need to be replaced due to wear and damage by corrosion.
If you want to do it yourself, you’ll need tools like the right sockets, ratchets, carb spray cleaner, gas and oil siphon and a carb kit if you’re rebuilding. If it’s your first time rebuilding a carburetor, it might take a while. Make sure to look at the manual and tutorial videos for assistance. But once you get familiar it won’t take long.
4. Faulty Choke
A choke is just a metal flap which prevents air from entering the carburetor. This helps a cold engine warm-up by creating a richer fuel mix. When the engine has warmed up, the choke is turned off which opens the flap again.
Now if the choke is bad, the flap won’t open, and the engine will get too much gas and no air. It will cause the engine to stall. Identifying a faulty choke is hard and fixing it is an issue if it’s your first time. It also depends whether your engine has a manual flap, automatic flap or no choke and a primer bulb instead.
Tips to Prevent Your Lawn Mower From Dying
Now that you know about all the common causes and their solutions, you might be asking yourself – What can I do to prevent it?
Besides basic maintenance and winterizing, you can follow some precautionary measures to ensure that your mower won’t stall and roar to life on the first pull. You will find various recommendations in the owner’s manual, but here are some useful tips.
- Clean your carburetor and carburetor bowl with a carb spray cleaner.
- Clean the air filter regularly and replace it annually or whenever the need is there.
- Keep the engine clean using a degreaser.
- Don’t overfill the oil reservoir; use a dipstick to measure the oil level.
- Change spark plugs every season or annually, and keep a spare one with you.
- Keep the gas clean by using a gas stabilizer.
Fixing a mower that at least starts is not as hard as it may seem. Most of the time, the problem is resolved by cleaning/rebuilding the carburetor or replacing the air filter. Over time, grease and dirt cause them to clog, which curtails the power supplied to keep the mower running.
The best way to minimize such events is regular maintenance which does not cost a lot and will save you a lot of time and energy. Other important things you need to keep in mind is to always keep the carburetor, air filter and the engine oil clean. We also suggest keeping a spare spark plug in case of emergency.
You can follow the methods we discussed to try fixing it yourself, but there’s no harm in seeking professional help which will make short work of your mower without any headaches. But there’s always that feeling of accomplishment when taking up the challenge yourself.