By: Author John Cunningham. Published: 2020/01/28 at 4:48 pm
Running out of gas happens to me all the time. After all, mowers don’t have a fuel gauge. But when your mower won’t restart after refilling, you may be left wondering what you did wrong.
Lawnmower ran out of gas won’t start? The most likely cause of a no-start mower after running out of gas is dirt in the carburetor, but other possible causes include:
- Air locked gas system
- Faulty carburetor
- Contaminated gas
- Faulty auto choke
- Faulty coil
In this short post, I’ll share why dirt in the carburetor is the most likely cause of the no-start. But we’ll also cover other possible causes.
This post covers your problem pretty well, but if you need video help, check out “Carburetor cleaning video.” It covers the removal, strip down, cleaning, rebuild, and carburetor refit procedure, step by step.
Dirt in the carburetor is, as you know, the most likely cause of the no-start. No, it’s not a coincidence that it happens at the same time as the gas tank runs flat.
It is, as you’ve probably guessed, a result of the mower sucking the bottom of the gas tank, and that’s where all the crap lives. Your mower should have a gas filter fitted, but they don’t catch everything. Besides, the sediment in the bottom of the tank is usually so fine it has no problem passing through the fuel filter.
The fix is to clean the carburetor. Some carburetors are easier to work on than others. So, just before we pull the carburetor apart, we can try a quick fix – Draining the carburetor bowl.
This is a simple job and will very often fix the problem. (more on that below)
Air-locked Gas System
Just before we get to the carburetor cleaning quick fix, I want to introduce the next highly possible cause of a no-starting mower. And that is an air-locked fuel system.
The reason I mention this now is that the fix for air-locking is the same as the carburetor cleaning quick fix. So we’ll be killing two birds and all that. You may be asking why your fuel system air-locks when your mower runs out of gas.
Dry gas tank – A dry gas tank is also prone to air-locking.
When the fuel lines run dry, they are replaced with air. Refilling the tank pushes the air toward the carburetor. However, if the gas tank isn’t filled to the top, the weight of the gas may not be sufficient to push the air completely out of the system.
Trapped air in the fuel lines means no gas getting to the engine. The usual fix is to release the air by opening the carburetor bowl drain, but just before we do that, we’ll try to release the airlock by tapping on the gas bowl.
Tap – Try tapping on the bowl with the gas cap removed before moving on to opening the gas bowl drain bolt.
Carburetor Bowl Drain
Draining the carburetor bowl is a simple job. Many engine manufacturers include a separate drain bolt in the bowl which makes the whole job super easy. The carburetor fuel bowl is located behind the air filter and attached to the underside of the carburetor. The fuel bowl or gas bowl is a reservoir of fuel. Its job is to store enough gas to feed the engine.
The fuel bowl is designed to catch debris that makes it past the filter. There are two common types of fuel bowls: those that have a useful drain bolt and those that don’t.
Draining the bowl will release trapped dirt and air from the fuel system. It’s not a substitute for cleaning the carburetor, but as said, very often draining the bowl for a few seconds or so is enough to clear the debris.
Carburetor bowl drain bolt – This model has a drain bolt, so the bowl doesn’t necessarily need to be removed.
With the bowl drain removed, the gas should flow freely from the carb; if not, check out the fuel filter and needle seat for possible blockage.
Carburetor bowl removal – This is a common B&S engine, and the bowl needs to be removed to drain the bowl.
In addition, it’s very important to clean the fuel feed bolt; this is the most common cause of no starts on this type of engine.
With the bowl removed, the gas should flow freely from the carb; if not, check out the fuel filter and needle seat for possible blockage. If draining the bowl worked out for you, fantastic, but if it didn’t, check out this guide on “Carburetor cleaning”.
It’s worth noting small engine carburetors cause lots of issues. I replace a ton; the symptoms can vary widely.
But hot starting issues are definitely one of them. However, the customer usually complains about hard starting issues all the time, not just after running out of gas. Some carburetors will be very obviously damaged (corrosion), but most won’t show any visible signs of damage or wear.
A faulty carburetor is on the list of suspects and will move higher on the list if you have removed the carburetor, cleaned it, and it made no difference.
It’s worth checking the gas can you use to fill the mower. We’ve all done it; put something other than gas in the mower. It’s a simple mistake, especially if you’ve got some old gas cans from last season.
Gas only stays fresh for about a month; after that, it can cause all sorts of running problems in a small engine. If you think your gas is the problem, go ahead and drain it out, put some fresh gas in, and she should fire straight up. If she doesn’t, go ahead and drain the gas bowl as per above.
If you find you don’t use up all the gas within a month, either buy less or use a gas stabilizer in the gas can. It keeps the gas fresh for up to two years, and better than that. It protects the fuel systems of all your small engine equipment, including a two-stroke kit.
You can check it out here on “Small engine repair tool page.”
Faulty Auto Choke
Auto choke is, as you may know, a feature that most modern mowers have as standard. Briggs and Stratton call theirs “Ready start.” The auto choke systems are very good, but they aren’t without fault. Auto chokes can stick in the on position, causing the engine to flood.
This, however, doesn’t have any relationship to a mower running out of gas; that may simply be a coincidence. A sticking auto choke can present as an intermittent issue or a constant. You can easily check if the choke is functioning correctly. Remove the air filter when the mower’s hot; the choke plate shouldn’t be closed.
Auto chokes “On” – This is the correct choke position for a cold engine, but not a hot one.
Auto Choke “Off”
The final component on our list is the coil also known as the armature. The coil helps make the spark needed to ignite the gas inside the engine.
Coils have a tough job and are a common failure. A very common symptom of a failing coil is intermittent hot start problems. While I know this isn’t exactly a fit for your symptoms, as a failing coil has no relationship with a mower running out of gas, that’s why it’s at the end of our list.
You can easily and quickly check your mower for spark. I’ve covered it in this post “Mower hard to start when hot”
Spark Plug Test
How do you fix a mower that won’t stay running? The carburetor needs to be removed and cleaned. If the carburetor is badly corroded, it will need to be replaced.
- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.