What Type of Gas Does a Weed Eater Use?

On this page (9 sections)

1. What type of gas does a weed eater use?
2. Why straight gas ruins a 2-cycle engine
3. What ratio should you mix for your trimmer?
4. Should you use ethanol-free gas?
5. Which oil goes in a weed eater?
6. How do you fill and start a gas weed eater?
7. How should you store mixed fuel and the trimmer?
8. What mistakes should you avoid with weed eater fuel?
9. The bottom line on weed eater fuel

A gas weed eater uses regular unleaded gasoline mixed with 2-cycle oil, usually at a 50:1 ratio. Straight pump gas damages a 2-cycle engine, so you add oil before the fuel ever reaches the tank.

That one step is the whole answer to what type of gas does a weed eater use, and getting it wrong is the most common way these trimmers fail.

The rest is about octane, ethanol, the right oil and how to mix and store the fuel so the engine starts easily every time. Each part is simple once you know what your trimmer expects.

What type of gas does a weed eater use?

Regular unleaded gasoline with 2-cycle oil mixed in. A weed eater engine is a 2-cycle design, so it has no separate oil sump and the oil has to travel with the fuel.

Without that oil, metal rubs on metal and the engine seizes.

Use pump gas at the octane the maker lists, which is usually 87 or higher. Avoid fuel with more than 10 percent ethanol when you can.

Most makers specify mid-grade or regular, so don't pay for premium unless your manual calls for it.

The mix ratio matters as much as the fuel. A 50:1 mix means 1 part oil to 50 parts gas.

Too little oil wears the engine, and too much oil fouls the plug and clogs the exhaust.

Why straight gas ruins a 2-cycle engine

Straight gas contains no oil, so the cylinder runs dry. The piston and ring are lubricated only by the oil in the fuel, and that film disappears within minutes of running on plain gas.

The engine may start and run normally at first, which is what makes the mistake so easy. Then it loses compression, gets hard to start and eventually won't run at all.

A scored cylinder usually means a rebuild or a new trimmer.

If straight gas gets into the tank by accident, stop the engine and drain it right away. Add the correct mix and run it briefly, and have a small engine shop look at it if it sounds rough afterward.

The repair costs more than a can of 2-cycle oil, so mix carefully every time.

What ratio should you mix for your trimmer?

Most trimmers call for 50:1, but some brands ask for 40:1 or 32:1. The ratio is printed on the fuel cap or in the manual, and that is the number to follow for your exact model.

To mix a small batch, pour the oil into a clean fuel can first, then add the gas. That order helps the oil blend evenly instead of sitting in a layer.

Shake the can gently before each fill.

Mix only what you'll use in about a month. Fuel that sits loses its punch, and stale mix is a leading cause of hard starting.

Should you use ethanol-free gas?

Yes, ethanol-free fuel is the better choice when you can find it. Ethanol absorbs moisture from the air, and that water collects in the carburetor and fuel lines of a small engine.

Ethanol-free gas also stores longer, so a can lasts through a few weekends of trimming.

Most pump gas in the US contains up to 10 percent ethanol. That E10 fuel works fine in a trimmer you use weekly and keep fresh.

For a trimmer that sits a lot, buy ethanol-free at a marina or hardware store, or use a pre-mixed canned fuel.

Canned fuel costs more per gallon but needs no measuring and stays stable for a long time. For occasional homeowners, it's the easiest way to avoid a gummed carburetor.

Whatever you choose, never top off a tank with fuel left over from last season.

Which oil goes in a weed eater?

Use oil made for air-cooled 2-cycle engines, and match it to the maker's recommendation. Husqvarna, for example, sells its own 2-cycle oil, and mixing that with pump gas is the safe route.

Many makers specify a synthetic blend for cleaner running and less smoke.

Don't use 4-cycle motor oil, outboard oil or two-stroke oil for water-cooled engines. Those products don't burn the way an air-cooled weed eater needs.

The wrong oil leaves carbon deposits and can foul the spark plug quickly.

Measure oil with the markings on the bottle or a small measuring cup. Guessing at the ratio is how engines end up with too much or too little oil.

A small bottle of the right oil protects a trimmer worth far more.

How do you fill and start a gas weed eater?

Fill the tank outdoors on a level surface with the engine off and cool. Use a funnel to avoid spills on the housing or the ground.

Wipe up any drips before starting.

Set the choke, prime the bulb if your model has one, and pull the starter with a firm, steady motion. Push the choke in as the engine warms.

If the trimmer floods, wait a few minutes with the choke open, then try again without priming.

The Husqvarna 122RJ runs a string trimmer head and a grass blade on mixed fuel. It adds a barrier bar and a J-handle for heavier clearing jobs.

For a lighter yard, the Husqvarna 122LK uses a SmartStart recoil system designed to reduce pull effort. Its 22cc 2-cycle engine is built for occasional homeowner use and comes with the T25 head.

For bigger overgrowth, the Wild Badger 52cc kit pairs an 18-inch string trimmer with a 10-inch brush blade. Its full-crank engine is built for denser grass and brush than a light homeowner trimmer.

How should you store mixed fuel and the trimmer?

Use mixed fuel within about 30 days and store it in a sealed, labeled gas can. Keep the can out of direct sun and away from the house.

Label it clearly so no one pours it into a 4-cycle car or mower.

For the off-season, drain the tank and run the engine until it stops on its own. That empties the carburetor so fuel can't turn to varnish inside it.

A fogging oil or a fuel stabilizer helps if your manual calls for one.

Store the trimmer upright in a dry spot. Our guide to how to store a weed eater in the garage covers hanging, fuel and winter prep in more detail.

If you're weighing a cordless trimmer instead, our look at how long a weed eater battery takes to charge shows what changes without fuel.

What mistakes should you avoid with weed eater fuel?

The big ones are straight gas, stale mix and the wrong oil. Each one causes hard starting or engine damage that a little care would prevent.

A few smaller habits matter too.

Don't mix fuel in the trimmer tank. Measure in a can so the ratio stays exact.

Don't leave fuel in the tank for months, and don't reuse old mix from last season.

Don't fill the tank to the very top. Leave a little room for the fuel to expand.

Don't store the trimmer on its side with fuel in it, since it can leak into the carburetor or the air filter.

If you're still shopping, our guide to how to choose a weed eater compares gas and cordless models for yard size. And if you end up with a corded electric model instead, check what type of extension cord a weed wacker needs before you plug in.

The bottom line on weed eater fuel

Mix regular unleaded with 2-cycle oil at the maker's ratio, and a gas weed eater will run cleanly all season. Use ethanol-free fuel when you can, keep the mix fresh and never run straight gas.

That covers what type of gas does a weed eater use, from the first tank to winter storage.

Pick a 50:1 mix for most trimmers and follow the cap or manual if yours differs. Buy the oil the maker recommends, measure it carefully and label your fuel can.

For heavy brush and overgrowth, the Husqvarna 122RJ brush cutter puts the same mixed fuel to the hardest work. For a light yard, a 22cc trimmer like the Husqvarna 122LK is easy to keep fed, while the 52cc Wild Badger kit sits in between with its brush blade.

Whichever you run, fresh fuel and the right oil are the cheapest maintenance you'll ever do.

Frequently asked questions

Can I put straight gas in a weed eater?

No. A 2-cycle weed eater engine needs oil mixed into the gas to stay lubricated.

Straight pump gas will run it for a short while and then seize or score the cylinder.

Mix fresh fuel with 2-cycle oil at the ratio the maker specifies before you fill the tank.

What gas mix does a weed eater take?

Most gas weed eaters run on a 50:1 mix, which is 1 part 2-cycle oil to 50 parts gasoline. Some brands call for 40:1 or 32:1.

Check the fuel cap or manual for your model's ratio, and use the oil the maker recommends for it.

Is ethanol-free gas better for a weed eater?

Yes. Ethanol-free gas stores longer and doesn't pull moisture into the carburetor the way E10 can.

Small 2-cycle engines are more sensitive to ethanol, so buying ethanol-free fuel or a pre-mixed canned fuel reduces gumming and hard starts, especially when the trimmer sits between jobs.

Can I use 4-cycle oil in a 2-cycle weed eater?

No. 4-cycle oil is not designed to burn with the fuel and won't lubricate the cylinder properly.

Use only oil labeled for air-cooled 2-cycle engines.

The wrong oil can foul the spark plug and score the piston, which usually costs more than the oil you saved.

How long can mixed weed eater gas sit in the tank?

Mixed fuel is best used within 30 days. Gasoline loses its lighter compounds and the oil can separate, which leads to hard starting.

Drain the tank and run the carburetor dry before storing the trimmer for the season, and mix fresh fuel when you start again.