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Understanding Vapor Lock in Lawn Mowers

Understanding Vapor Lock in Lawn Mowers

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Paul Brown

Vapor lock in lawnmowers generally occurs during hot summer days and result in your mower stalling or simply not working at all. This issue occurs because the fuel in the fuel delivery system can overheat and vaporize, preventing fuel delivery to your mower. 

In this article, I’ll explain the causes of vapor lock in more detail. I’ll also offer you some solutions so that you don’t have to worry about your Homeowner’s Association coming after you for an unmowed lawn.

What Causes Vapor Lock in Riding Lawn Mowers?

Vapor lock in riding lawn mowers is a result of the fuel overheating and turning to gas. However, your mower is designed to pump liquid gas, not air. This causes the gas bubbles to accumulate, which, in turn, prevents the liquid gas from pumping to the engine.

Without fuel, the engine either stops working entirely or starts and stalls, both of which can be highly annoying.

While the summer heat is the most common cause of vapor lock, leaving a mower near very hot objects such as a working barbeque or fire pit can also increase the risk of your mower developing a vapor lock. 

This is especially true if it happens during the summer when the heat is already a problem.

How To Prevent Vapor Lock in a Lawn Mower

Vapor lock is undoubtedly one of the most annoying issues that your lawn mower can face. Luckily, preventing vapor lock is a relatively simple task. Let’s now talk about what you need to do.

Use Fresh Fuel

Did you know that fuel can go stale?

That’s right, gasoline can go stale, and it doesn’t take long. In fact, in as little as 30 days, the gas inside your mower will have degraded and become significantly less combustible, and therefore, less effective. 

It also increases the risk of vapor lock since the gas won’t burn, allowing it to get hot enough to vaporize instead (source).

Luckily, you don’t need to refill your gas every month. What you should do instead is be conscious of what fuel you’re adding to your mower and avoid fuels that include alcohol or ethanol. These fuels are meant for larger cars, not smaller lawn mowers.

You can encounter a lot of issues when using gas from your local station pump which I explained in this article. One of the advantages of using an ethanol-free gas is that it has a longer shelf life.

Additionally, get into the habit of adding a fuel stabilizer to your tank every time you fill it up. This helps increase the lifespan of your gas.

You can use a product like Star Brite Star Tron Enzyme Fuel Treatment (link to Amazon). It helps stabilize fuel for as long as two years, so you’re unlikely to ever have to worry about the condition of your fuel. 

Your mower will likely need to be refilled before this product stops working.

If you’ve never used a fuel stabilizer before, you can refer to this YouTube video to understand how to use it in your lawn mower. As the video points out, a fuel stabilizer is also a great way to protect your mower’s engine during the winter.

How to Winterize your Lawn Mower with Fuel Stabilizer

Protect Your Fuel Lines

This is perhaps one of the easiest solutions you have to prevent vapor lock. All you need to do is install heat-resistant sleeves on your fuel lines.

These sleeves are precisely what they sound like. They prevent your fuel lines from heating up, which means that the gas inside them won’t be able to overheat and vaporize, and you won’t have to worry about vapor lock issues.

Take Care of Your Engines

Knowing how to take care of your mower engine can help keep it clean.

  • Clean around the airflow areas, such as the air intake and the cooling fins. This helps keep your engine, and the fuel inside, as cool as possible, as dirt can act as an insulating and heating material.
  • Don’t use water to wash your engines. Instead, use compressed air or a soft brush. Additionally, check the engine and surrounding areas for mice and insect infestations.

Check the Fuel Tank Cap

One way that mowers are designed to reduce the risk of vapor lock is through the cap on the fuel tank. These caps usually have a small vent hole that allows air to flow through, reducing the risk of overheating.

If the cap is dirty, there’s a chance that the vent hole is blocked. Cleaning your fuel tank cap is possible, but if the cap is too dirty, replace it with a new one.

See Lawnmower Spits Gas Out of Fuel Cap: Reasons and Fixes

Keep an Eye on the Temperature

If you’re unable to implement any of the solutions mentioned above, there’s another simple fix – keep an eye on the temperature outside.

The possibility of vapor lock increases when temperatures are high and the engine is running for an extended period of time. Consider mowing your lawn in the morning and evening if possible and avoiding the worst of the midday and afternoon heat.

Additionally, make sure you’re not leaving your mower near a hot object that can increase the likelihood of vapor lock.

If you have to mow during the hottest hours of the day, make sure to take as many breaks as possible. Keep an eye out for any early signs of vapor lock, like sputtering, and stop mowing immediately if you think there’s an issue with your mower.

Final Thoughts

With proper care, your lawnmower should last you for years. If your mower does experience vapor lock, all you need to do is vent the engine.

Move your mower into the shade and open its hood. Let the engine vent and pour cold water over the fuel lines, pump, and bowls. Once vented, press the accelerator slightly to remove any leftover vapor in your fuel lines.

Once your mower engine is fully vented, it should be ready to get back on your lawn!

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