Let’s take a look at some of the most common issues that can cause your lawnmower to start up, then stall and die. We will also offer some tips and advice on how you can fix these issues.
What Is the Most Common Lawnmower Issue?
The most common lawnmower issue is that the carburetor is dirty. If your lawnmower is starting and then stalling, the most likely issue is the carburetor. Here's what you need to know about how a dirty carburetor can cause a lawnmower to start, then stall out and die.
A Dirty Carburetor Can Cause a Lawnmower to Start Then Die
By far, the most common issue that causes a stalled motor is a dirty carburetor. The carburetor on your engine is the thing that draws in air and mixes it with the fuel. Contrary to what the movies might make you think, gasoline itself is not very flammable. It only becomes extremely flammable when it’s mixed with air.
How Does a Carburetor Work?
The carburetor draws in air from the surrounding environment and mixes it with fuel in the right ratio. If your carburetor is dirty, then it is not mixing air properly, and the gas won’t combust. This will mean that your engine will sputter a bit, but it won’t really kick into gear.
Here are a few things you can check that signify a dirty carburetor.
What Are Signs of a Dirty Carburetor?
- Engine Stalling or Surging: If the engine stalls frequently or surges (revs up and down) unexpectedly, it could be due to a dirty carburetor. Dirt or debris obstructing the carburetor's passages can disrupt the fuel flow and air mixture, leading to erratic engine performance.
- Hard Starting: Difficulty starting the engine, especially when it was previously running fine, can be a sign of a dirty carburetor. If the carburetor is clogged, it may not be delivering the correct amount of fuel and air for starting the engine.
- Poor Fuel Efficiency: A dirty carburetor can cause the engine to run rich (too much fuel) or lean (too little fuel), both of which can decrease fuel efficiency. If you notice a sudden drop in fuel efficiency without any other apparent cause, it could be due to carburetor problems.
- Black Smoke from Exhaust: If you see black smoke coming from the exhaust, it may indicate that the engine is running too rich, which could be caused by a dirty carburetor. Excess fuel not properly atomized and burned can result in black smoke emissions
What Causes Lawnmower Carburetor to Clog?
When your carburetor is clogged, the cause is likely to be evaporated gas that has gummed up the pores. When gas is left in the tank, over time, it will evaporate. Gas contains ethanol, which can settle in your carburetor’s pores, which are supposed to channel air. The evaporated gas can then condense inside the carburetor, gumming up the works and making it unable to do its job. In most cases, cleaning and resetting the carburetor will fix the problem, and your mower will start running properly again.
How to Fix a Dirty Carburetor
Your best bet is to remove and clean your carburetor. Here are some tools you will need to fix it.
- Sockets and a ratchet: You will need a socket wrench to remove the carb. Consult your owner’s manual to figure out what size socket you need.
- Gas siphon: A gas siphon will remove any excess gas and oil from your engine. A good gas and oil siphon can save you a lot of time instead of manually draining the tank and oil repository.
- Carb cleaner solution: You can use rubbing alcohol to dissolve any dried and gummed-out gas, but it is probably a better idea to get a can of carburetor cleaner. This aerosol can have a directional straw and is designed specifically to dissolve the gas residue.
- Fuel treatment solution: While not necessary, a fuel treatment solution can improve your engine health and keep gas from drying out and gumming -up your carb in the future. You can buy both a carb cleaning solution and fuel treatment solution from your local home & garden store.
How to Clean a Dirty Lawnmower Carburetor
To clean your lawnmower’s carburetor, follow these steps.
1. Inspect the Air Filter
The first thing you'll want to do is to take a look at the air filter. If the air filter is dirty, you can scrape the gunk off, and your carburetor should start working properly again. One common symptom of a dirty air filter is black smoke coming from the exhaust.
2. Check the Connections
If the air filter is not the culprit, then next move on and check the connections: The connectors between the throttle and choke plates can get sticky when dirty. The screws can also be worn down from the constant vibration. If the screws are too stripped, you might have to replace your carb with a new one.
3. Clean the Carburetor
If the connectors are not the problem, you will probably have to remove the carb and give it a thorough cleaning. Detach the choke and throttle linkages from the lever and gently slide the carburetor off its mounting bolts. At this point, you might need to unscrew some parts to take the entire carburetor apart. Detach the primer from the base and remove the metering plate and gasket. Now that you have the internal components exposed take your carburetor cleaning solution and spray the inside of the ports to clean out any residue. You can also take a soft cloth and give it a thorough wipe-down once you are done.
4. Examine the Carburetor's Fuel Bowl
You should check the bowl of the carburetor as well. The fuel bowl contains a small reservoir of gas that feeds the engine to keep it burning. Over time, the fuel bowl will collect stale gas, which will evaporate and form a residue. The fuel bowl is usually located behind the air filter. It has a distinctive bowl shape, so you can’t miss it.
5. Clean Off any Rust
You might also find that your carburetor has some rust built up. It’s probably a good time to clean off this rust. You can clean it off with some sandpaper to remove the rust.
6. Reassemble the Carburetor
Once all the components are spic-and-span, you can reassemble the carburetor and reattach it. Ensure that all the diaphragms, gaskets, metering plates, and primer are attached properly before you reattach it back to the engine. If something is off, you might still experience the same problem as your engine starting and sputtering out.
7. Reattach Everything and Fire Up the Lawnmower
Once the carburetor is reattached, put the fuel line back in and reinstall the air filter housing. Once everything is back together, put some gas in your lawnmower and give it a rip to see if that fixed the issue.
If your lawnmower still has issues due to the carburetor, check to see that all the components have been reconnected properly. If the issue still persists, then you might want to look into getting a new carb to replace your old one.
How to Stop Your Lawnmower Carburetor from Clogging
The best way to prevent a clogged carburetor is to take it off and clean it relatively frequently. Try to clean your carb once after every couple of uses or after you have left your mower in storage for a while.
You can also prevent clogging by buying a high-quality mower. Briggs and Straton is a well-known brand whose lawnmowers are made of quality components that are resistant to rusting and gumming out from dried-up gasoline.
Lawn Mower Starts Then Dies Bottom Line
When you bring out your trusty lawnmower and start it only for it to sputter and stall out, it can be very frustrating. Your first instinct might be to call a pro and have them give your lawnmower a checkup, but that can be expensive and cost you a couple hundred dollars for a diagnosis. Besides, once you figure out why your lawn mower starts then dies, you can often solve the problem yourself. The issue might be something common, like a clogged carburetor, which you can handle and fix yourself.