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Why Is My Lawn Mower Turning Over but Not Starting?

Lawn mowers are powered by gasoline and are used to cut grass in an area. The fuel system of these machines is relatively easy to maintain and repair. 

Because they were originally designed with gas-powered engines, they can also run on propane or natural gas which has a smaller storage tank than gasoline.

But oftentimes, these machines turn over, but not start. There are many reasons why a lawn mower may turn over but not start. One of these reasons is that the fuel line is clogged with debris or clumps of grass. 

Another reason why your lawn mower may turn over while not starting is that there’s too much gas in the tank and it could overflow, causing it to overflow onto the ground and possibly causing an explosion.

This article will explain what could be the cause of a lawn mower turning over but not starting. Let’s get started.

Reasons behind lawn mower turning over but not starting

  1. Partially restricted carburetor
  2. Varnish in the carb
  3. Choke plate might not close fully
  4. Bad gas
  5. Faulty spark plug

Partially restricted carburetor

A lawn mower carburetor is an important part of the engine of your lawnmower. It is a device that mixes the fuel with air and sends it to the engine to get power.

A partially restricted carburetor of a lawn mower engine
A partially restricted carburetor

When the carburetor is partially restricted and it turns over, but not starts, there are a few things that may cause this problem.

One reason for this could be varnish build up in the carburetor. Gas cannot flow well when this happens because the passageways have become clogged up with varnish.

To prevent the lawn mower from turning over but not starting, you might try to use fuel additives. But the use of fuel additives won’t stop the process, but it will greatly slow it down but gas will still go bad eventually. 

The engine will run at choke on and will stop. It might run but is likely to surge.

Varnish in the carb

Another cause of a lawn mower not starting is varnish in the carb. The carburetor is responsible for the engine’s need for air and fuel in the engine. If there is a varnish buildup in the carb, it may not allow the float needle to seal. 

Dirt on carburetor of a lawn mower engine
Dirt on carburetor

Varnish build-up can affect a carb’s ability to seal and stop gas from flowing when needed. This may lead to flooding of your engine if there’s too much gas in your carb before you start it up. 

Gas gets into the cylinder by seeping past the rings to the crankcase. It’ll show an over-full oil or gas smell in oil.

Bad gas

When the gas sits in the tank for too long, it can play tricks on your lawn mower. The gas turns into a thick sludge and clogs up the fuel line and carburetor. 

Testing for gasoline in lawn mower, draining gas
Testing for gasoline in lawn mower

For this reason, when you try to start the engine, it turns over but doesn’t start as you might expect.

Choke plate might not close fully

The choke plate’s function is to limit the amount of air going into the carburetor and throttle body in order for the engine to start. When it doesn’t close completely, some of the air left inside can leak out, causing engine stalling. 

Your mower’s choke might not close completely. This will cause the engine to not start.

Faulty spark plug

If you have a lawn mower and it is getting hard to start, there are a few ways that you can tell if the problem is with your spark plug. One of these ways is through the color of your engine oil. 

Faulty spark plug of a lawn mower
Faulty spark plug

If it’s black and oily, then chances are that your spark plug doesn’t work properly and causes deposits of oil in the engine. This deposited oil then prevents the engine from starting fully. 

If the oil appears to be wet, then it means that too much fuel might have been added to the engine instead of just enough. Where dry spark plug may appear as a block fuel system fault with the choke.

Your lawn mower might backfires due to faulty spark plug. To avoid this problem, make sure that you are using spark plugs that are in good condition so they can perform well in any conditions.

Frequently Asked Questions

How do you force start a lawn mower?

Lawn mowers can be manually started by pulling the cord on its handle or by turning an engine key. However, what should you do if your lawn mower’s engine won’t start?

If you are looking for a quick and easy way to force start a lawn mower, there is a common and easy solution. Try to spray engine starting fluid on the air filter and start it. 

Try turning on your mower and see if it starts up. If it starts up and stays running, then you are good to go!

Can a lawn mower get flooded?

Yes, it can, but typically the mower itself is water resistant and can be used for a short period of time after it has been submerged.

The issue with flooding is priming the mower too many times. The water will find its way into the engine and cause serious damage. Another cause is to try to start it too many times pulling the start cord loosely. 

If you have a riding lawn mower, it may be better to keep it away from any bodies of water until the flood subsides.

Why is my lawnmower cutting out?

There are two main reasons why your lawnmower may be cutting out. The first one is a faulty power switch, which is usually caused by a loose cable connection. 

The second reason is an overheating motor which causes the thermal cut out to trip.

The most common cause of a faulty power switch is that the wires are not connected properly and they are touching each other while it’s running. A loose wire connection can also cause the lawn mower to cut out.


In this article we’ve discussed the reasons behind a lawn mower that turns but does not start. And also some possible fixes. Follow our advice to get your lawnmower run again. 

If you have trouble solving this issue, get help from professionals.

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