Ryobi offers gas-powered string trimmers, often called weed eaters or weed wackers, with either a 2-cycle or 4-cycle engine.

You must know which type of engine is on your model string trimmer to avoid adding the wrong fuel. Using the wrong fuel in your trimmer can result in having to purchase a new replacement string trimmer.

Ryobi string trimmers use unleaded gasoline with a minimum 89-octane rating and a maximum ethanol content of 10%. Ryobi string trimmers with 2-cycle engines require oil to be mixed with gasoline.

Ryobi string trimmers with 4-cycle engines will have separate fill ports, one for fuel and one for oil.

If you are unsure what type of engine you are running on your Ryobi string trimmer, refer to your operator’s manual. You may also find this information on the original fuel cap which may have an image of a fuel pump and oil can. It may even indicate the gas-to-oil ratio on the cap.

This post may include affiliate links. Purchases made through these links may provide a commission for us, at no extra cost to you. As an Amazon Associate, we earn from qualifying purchases.

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.

Old or Bad Gas in a Ryobi String Trimmer

Gas can be the root of many problems developing in a Ryobi string trimmer including not starting, bogging down, and loss of power. This is because gas can begin breaking down becoming less effective as soon as 30 days after purchase.

Most gasoline contains ethanol. This is a plant-based fuel, often made of corn, that makes gas more environmentally friendly. It is a product that may be better for the environment but isn’t good for the small engine on your Ryobi string trimmer.

When gas ages, it leaves behind a varnish with sticky deposits that will clog the fuel system.

Ethanol naturally attracts moisture from the air that can corrode components on the string trimmer and be harmful to the engine when the water and ethanol mixture separates from the gas and runs extremely hot when burned.

Because gas breaks down quickly, it is important to use fresh gas. Add a fuel additive like Sea Foam Motor Treatment to stabilize your gas and reduce moisture so it lasts a little longer.

Ryobi string trimmers require unleaded gasoline with a minimum octane rating of 89 and a maximum ethanol content of 10% (E10). If your Ryobi trimmer has a 2-cycle engine, mix a 2-cycle premium oil with the gas before adding it to the fuel port.

Avoid gasoline that includes ethanol contents greater than 10% including fuels sold as E15, E30, or E85. These fuels contain up to 15%, 30%, and 85% ethanol respectively. Ethanol-free fuels are best and will reduce the issues you experience due to old fuel.

Ethanol-free fuels can be found at your local hardware store or online. They can also be found at select fuel stations sold as recreation fuel (REC-90). Look for a fuel station near you at pure-gas.org

Ethanol Free Fuels for String Trimmers

• 2-Cycle 50:1 Premix
• 4-Cycle Fuel

Gas and Oil to Use in a 2-Cycle Ryobi String Trimmer

2-Cycle Gas and Oil Mix in a Ryobi String Trimmer

All 2-cycle Ryobi string trimmers require a 2-cycle premium oil to be added to gas before adding it to the fuel tank. Don’t make the mistake of adding straight gas to your 2-cycle string trimmer.

This will cause the engine to seize up and no longer run. This is because gas runs very dry. Without the lubrication provided by the addition of oil to the gas, the internal parts of the engine won’t be able to move freely.

Most likely, if you accidentally add straight gas to your string trimmer and start it, you will have to replace it with a new one. The engine will be damaged beyond repair.

Your Ryobi 2-cycle string trimmer uses a gas and oil mixture at a ratio of 50:1. This means 50 parts gas is mixed with 1 part oil. Refer to the chart below.

When creating this mix, use unleaded gasoline with a minimum octane rating of 89 (mid-grade) and maximum ethanol content of 10%. Add a 2-cycle premium oil that is ISO-L-EGD and JASO M345 FD certified.

Note: Some older Ryobi 2-cycle string trimmers use a mix at 32:1. You can find the mix ratio for an older string trimmer in your owner’s manual.

How to mix gas and oil for a 2-cycle string trimmer:

• 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 the Ryobi string trimmer’s fuel tank.

You can use the manufacturer’s recommended Ethanol Shield 2-Cycle Oil. Another alternative is this 2-cycle mix by Kawasaki. It comes in 5.2 oz. and 6.4 oz. bottles that can be mixed with 2 gal. or 2.5 gal. of gas respectively for a 50:1 mix.

Using one of these brands of oil that already includes a fuel stabilizer helps extend the life of the gas and oil mix. Just make sure you consume the mix within 90 days.

2-Cycle Ryobi Gas to Oil Mix

2-Cycle Premixed Ethanol-Free Fuel

A great option to reduce fuel problems and extend engine life is using an ethanol-free fuel mix. This is an ethanol-free blend of oil and fuel that is ready to pour into your Ryobi string trimmer’s fuel tank. You won’t have to deal with the bad effects of ethanol as discussed in the fuel section.

It’s a convenient option to have fuel available on your shelf when you need it that’s not going to go bad as it sits. You can find a 50:1 premixed can of fuel at your local hardware store or online.

Gas and Oil to Use in a 4-Cycle Ryobi String Trimmer

Gas for Ryobi 4-Cycle String Trimmer

While 2-cycle Ryobi string trimmers have been on the market for many years, you will now find Ryobi string trimmers with 4-cycle engines. These types of engines have separate ports for fuel and oil so there is no need to mix fuel and oil.

4-cycle Ryobi string trimmers require unleaded gasoline with an octane rating of 89 or higher and an ethanol content of 10% or less.

It is best to add a fuel stabilizer like Sea Foam or STA-BIL to keep the gasoline from breaking down quickly and to help reduce moisture and gummy deposits in the fuel system.

While using gasoline with a low ethanol content is acceptable, it is not the best option available. The best fuel to use in a Ryobi string trimmer is an ethanol-free fuel available at the fuel pump at select fuel stations or in canisters at your local hardware store or online.

Ethanol-free gas is the more expensive choice. Purchasing in canisters is not only convenient, but it may also be a good alternative if you don’t want to deal with the potential headaches that can come from running old ethanol-based gas through a string trimmer.

Engine Oil in a 4-Cycle Ryobi String Trimmer

4-cycle engines have separate fill ports for the engine oil and the fuel. DO NOT mix the oil and fuel together for a 4-cycle engine. Never use 2-cycle oil in a 4-cycle string trimmer.

Oil is required to keep the engine components lubricated. When the wrong type or not enough oil is used, friction can build in the engine and overheat causing your string trimmer not to start and possibly ruin the engine. Ryobi recommends a 20W-50 engine oil.

The engine oil viscosity may need to be changed to one better suited for very hot or very cold ambient temperatures when you are using your string trimmer in these types of conditions.

For example, you may need to change your oil viscosity to a 10W-30 when operating your Ryobi trimmer in colder temperatures.

4-Cycle Ryobi Engine Oil Viscosity

In Summary

The fuel used in your Ryobi string trimmer affects performance. When fuel ages, it can cause corrosion and fuel restrictions. Follow these simple steps when choosing a fuel for your Ryobi string trimmer:

• Always use fresh gas.
• Make sure the gas contains no more than 10% ethanol.
• Know the type of engine on your Ryobi (2-cycle or 4-cycle).
  • 2-cycle: Mix gas and oil together before adding to the fuel tank.
  • 4-cycle: Use straight gas.
• Add a fuel stabilizer so your gas lasts longer without breaking down.
• Store gas in a dry location away from moisture and combustible products.