Using the wrong type of gas in your lawn mower can seriously damage the engine. This is one thing you don’t want to get wrong.

Lawn Boy has manufactured mowers with 2-cycle (2-stage) and 4-cycle (4-stage) engines that have different fuel requirements. Protect the investment you made in your mower by using the right gas and properly caring for it.

A Lawn Boy mower requires unleaded gasoline with a minimum octane rating of 87 and a maximum ethanol content of 10%. Lawn Boy 2-cycle lawn mowers use a gasoline and oil mix. Lawn Boy 4-cycle lawn mowers use straight gasoline.

This guide explains how to determine what type of engine you have, how to choose the right fuel, and how to care for that fuel.

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Choose the Right Gasoline for a Lawn Boy Mower

When selecting gas for your Lawn Boy mower, use fresh gasoline from a reputable source with a low ethanol content. I recommend using a fuel additive to stabilize the fuel and reduce moisture.

Low Ethanol Content

Ethanol, an alternative fuel used in gasoline today, can cause problems in the small engines used on Lawn Boy mowers. Ethanol attracts moisture from the air which is corrosive to the fuel system.

In addition, fuel and water will separate over time. The ethanol and water mixture will leave behind gummy deposits that can create fuel restrictions. It is very harmful to the engine when this mixture separates from the gas and runs hot through the engine.

Always choose low-ethanol gasoline that contains no more than 10% ethanol. The lower the ethanol level, the better. More and more fuels with ethanol are being sold at the local fuel stations.

Never use fuels sold as E15, E30, or E85. These fuels contain up to 15%, 30%, and 85% ethanol.

Use Fresh Gasoline

Gasoline can begin breaking down as soon as 30 days after purchase. It’s best to purchase the amount of fuel that can be used within 30 days to reduce damage to your Lawn Boy mower from fuel.

If you are unable to use the gasoline you purchased within this time, add a fuel additive to stabilize it so it lasts a little longer without breaking down.

Add a Fuel Stabilizer

I like to add Sea Foam Motor Treatment, a fuel additive to stabilize fuel, to every tank of gas. Sea Foam not only stabilizes gas, but it also cleans the fuel system and reduces moisture. It helps minimize problems that can develop from running old fuel.

Read more about using Sea Foam in, “Why Use Sea Foam Fuel Additive in a Lawn Mower“.

Ethanol-Free Fuel

Ethanol-free fuels are always best to run in your lawn mower, but it is a more expensive fuel choice. Ethanol-free fuel can be bought at some fuel stations often sold as recreation fuel or REC-90.

It can also be bought in canisters as a convenient option to store on the shelf in your storage shed or garage.

• 4-Cycle Fuel

Identify the Type of Engine on Your Lawn Boy Mower: 2-Cycle or 4-Cycle Engine

How to identify a 2-cycle or 4-cycle engine:

• Fuel Cap: An original 2-cycle fuel cap will have the gas-to-oil mix ratio listed on the cap (16:1 or 32:1) or it will show fuel and oil can on the cap.
• Number of Fill Ports: A 2-cycle engine will have one fill port for a gas-to-oil mix. A 4-cycle engine will have 2 fill ports. There will be one for engine oil and one for gas.
• Operator’s Manual: The manual that came with your Lawn Boy mower will list whether you need to use a mixed gas and oil mixture or straight gas.

Gas to Use in a 4-Cycle Lawn Boy Mower

Lawn Boy mowers with 4-cycle engines require unleaded gasoline with a minimum octane rating of 87 and a maximum ethanol content of 10%. Never use a mixed gas in your 4-cycle Lawn Boy mower. 4-cycle lawn mowers have two fill ports: one for gasoline and one for oil.

Gas and Oil Mix for a 2-Cycle Lawn Boy Mower

2-Cycle Gas and Oil Mix in a Lawn Boy Mower

Don’t mistakenly add straight gas to a 2-cycle Lawn Boy mower. If you do this and start your mower, it will most likely seize up and die. This is because a 2-cycle engine burns an oil and fuel mix.

Without the oil mixed with gas, the engine doesn’t get the lubrication it requires to run. Running straight gas will ruin the engine and you’ll be shopping for a new lawn mower.

Lawn Boy mowers with 2-cycle engines require gas and oil mixed at a ratio of 32:1. For example, 32:1 mix equals 32 parts gasoline to 1 part oil. The mix your mower requires varies by the age of your unit. If your mower is older than 1971, it requires a gas and oil mix at a ratio of 16:1.

If you have an older mower and you’re not sure when it was made, refer to your operator’s manual. You may also find it located on the fuel cap.

When creating this mix for a 2-cycle engine, use unleaded gasoline with a minimum octane rating of 87 and maximum ethanol content of 10%. Add a 2-cycle premium oil that is ISO-L-EGD and JASO M345 FD certified.

This oil from Lawn Boy works great. You can also purchase this 16 oz bottle from Briggs & Stratton which has a simple way to measure the amount of oil you require.

How to Mix Gas and Oil for a 2-Cycle Lawn Boy Mower:

• Use the chart below to determine how much fuel mix to prepare.
• Remove the cap from an approved gas can. Add unleaded fuel (minimum 89 octane rating & maximum 10% ethanol content) to a gas can.
• Using the chart for ounces of oil required, add the 2-cycle oil to the gas can.
• Replace the cap.
• Gently shake the fuel and oil until they are mixed.
• Add to your Lawn Boy’s fuel tank.

Lawn Boy 2-Cycle Gas to Oil MixChart

In Summary

Using the wrong kind of gas or old gas in your Lawn Boy mower can cause starting and running problems. Follow these quick tips when choosing and storing gas:

• Use straight gas in a 4-cycle engine and an oil and gas mix in a 2-cycle engine. Mix at the correct gas-to-oil ratio for your Lawn Boy model.
• Always use fresh gas and consume it within 30 days.
• Use unleaded gasoline with a minimum 87 octane rating and a maximum 10% ethanol content. The lower the ethanol content the better. Non-ethanol fuel is the best for the engine, but it is more expensive.
• Add a fuel stabilizer when you are unable to consume it within 30 days.
• Store gasoline in a dry cool location away from combustible products.