Stihl String Trimmer: The Complete Guide to Choosing and Using One

A Stihl string trimmer has earned a reputation among homeowners and professional landscapers as one of the most durable and reliable ways to tackle grass and weeds that a mower cannot reach. Whether you choose gas or battery power, understanding the lineup, the cutting heads, and proper maintenance will help you get years of dependable service. This guide walks through everything you need to know.

What Is a String Trimmer?

A string trimmer, sometimes called a weed whacker or line trimmer, uses a rapidly spinning nylon line to cut grass and light vegetation. The line spins fast enough to slice through soft growth by centrifugal force. Trimmers handle the edges, fence lines, tree bases, and tight spots your lawn mower deck cannot reach, giving a property that finished, manicured look.

Stihl, a German family-owned company founded in 1926, is one of the largest manufacturers of outdoor power equipment in the world. Its FS series of trimmers spans small homeowner units to heavy professional brushcutters built for all-day commercial use.

Gas vs. Battery Stihl Trimmers

Stihl offers both gasoline and battery-powered string trimmers, and the right choice depends on your yard and preferences.

Gas models in the FS series use a two-stroke engine, meaning you mix oil with the gasoline. They deliver strong, sustained power ideal for thick weeds, large properties, and professional workloads. The trade-offs are more noise, exhaust, vibration, and the need to keep mixed fuel on hand.

Battery models run on Stihl’s AK and AP lithium-ion systems. They start instantly with a trigger pull, run quietly, require no fuel mixing, and need far less maintenance. For small to medium suburban yards, a battery trimmer is often all you need. The professional AP system trimmers rival gas power but cost more and depend on battery runtime.

Understanding the FS Model Numbers

Stihl uses an FS prefix for gasoline trimmers and FSA for battery trimmers, with higher numbers generally indicating more power. A rough guide:

• FS 38 to FS 56: Homeowner gas trimmers for typical residential lawns.
• FS 70 to FS 91: Prosumer and light commercial units with more torque.
• FS 111 and up: Professional-grade trimmers and brushcutters for demanding jobs.
• FSA series: Battery trimmers, from the compact FSA 57 to the powerful FSA 135.

Engine displacement on gas models is measured in cubic centimeters, ranging from around 27cc on homeowner units to over 36cc on professional machines. More cc generally means more cutting power and the ability to swing thicker line or a metal blade.

The AutoCut and Line-Feed Heads

Stihl’s most common cutting head is the AutoCut, a bump-feed design. When the line wears down, you tap the head on the ground while it spins and centrifugal force releases a measured length of fresh line, which is then trimmed to length by a blade on the guard. It is simple, reliable, and rebuildable.

Stihl also offers fixed-line heads where you insert pre-cut line segments, and the TrimCut manual-adjust head. For heavy brush, many FS models accept metal grass blades or brush knives, dramatically expanding what the tool can cut. Always match line diameter to the machine; homeowner units typically use 0.080 to 0.095 inch line, while professional units run 0.095 to 0.105 inch or thicker.

Where to Buy: The Dealer Difference

Unlike many brands, Stihl is sold primarily through a network of independent servicing dealers rather than big-box stores. This is a deliberate choice. At a dealer, the unit is assembled, fueled, tested, and demonstrated before you leave, and you have a local expert for parts, repairs, and warranty work.

The trade-off is that you cannot simply grab one off a warehouse shelf or order the flagship models online for doorstep delivery in the same way as some competitors. For buyers who value service and longevity, the dealer relationship is a genuine benefit; for those who want the absolute lowest price and instant online checkout, it can feel like a hurdle.

How Much Does a Stihl Trimmer Cost?

Pricing spans a wide range based on power and features:

• Entry homeowner gas (FS 38, FS 56): Roughly $160 to $280.
• Prosumer gas (FS 70, FS 91): Around $300 to $450.
• Professional gas (FS 111 and up): $450 to $700 or more.
• Battery trimmers (FSA series): $150 to $250 as a bare tool, plus $100 to $300 for battery and charger.

Battery kits that include the battery and charger cost more upfront but save on fuel and maintenance over time. Because batteries are cross-compatible within a system, buying more Stihl battery tools spreads that cost.

How to Choose the Right One

1. Assess your yard size and the toughness of the growth you cut.
2. For small, tidy lawns, lean battery for quiet, fuss-free operation.
3. For large properties or heavy weeds and brush, choose a gas FS model with adequate cc.
4. Consider a loop handle for tight trimming or a bike-style handle for wide sweeping over big areas.
5. Visit a dealer to hold the units, since balance and weight matter over a long session.

Mixing Fuel for Gas Models

Two-stroke Stihl engines require a precise fuel-to-oil ratio, typically 50 to 1 when using Stihl HP Ultra oil. Getting this right is critical; too little oil starves the engine of lubrication and can seize it, while too much fouls the plug and creates smoke. Use fresh gasoline of at least 89 octane and mix only what you will use within a month or two.

Stihl sells premixed MotoMix fuel that stays stable for years, which is worth considering if you use the trimmer only occasionally and hate dealing with stale fuel. Ethanol-free gas is gentler on small engines when you can find it.

Loading and Replacing the Line

Reloading an AutoCut head is straightforward. The basic process:

1. Stop the engine and let the head cool.
2. Align the arrows on the head to open it, or twist the retainer as directed.
3. Cut a length of the correct-diameter line and fold it to find the center.
4. Seat the midpoint in the head’s channel and wind in the direction of the arrow.
5. Feed the ends through the eyelets, reassemble, and trim to length.

Winding the line in the wrong direction is the single most common mistake, so follow the arrows molded into the head.

Maintenance and Care

Regular upkeep keeps a Stihl trimmer running for a decade or more. Clean the air filter every few uses and replace it when dirty, since a clogged filter starves the engine. Check and replace the spark plug annually, and keep the cooling fins clear of grass buildup so the engine does not overheat.

At the end of the season, run the tank dry or add fuel stabilizer, since old ethanol fuel gumming up the carburetor is the number one reason trimmers fail to start in spring. For battery models, store the battery at a partial charge in a cool, dry place rather than fully depleted or fully charged.

Troubleshooting Common Issues

If a gas trimmer will not start, first suspect stale fuel, a fouled spark plug, or a clogged air filter, in that order. Bogging under load often points to a dirty air filter or a carburetor that needs cleaning or adjustment. If the line will not feed, the head may be wound too tightly, cross-wound, or out of line.

For battery units, a trimmer that suddenly stops may have tripped its overload protection from cutting material too thick; let it rest and cut lighter. Erratic power can indicate a battery reaching the end of its charge or a dirty contact. Excessive vibration usually means an unbalanced head or debris wrapped around the shaft.

Final Thoughts

Choosing a Stihl string trimmer comes down to matching power source and model to your property: battery for quiet convenience on smaller lots, gas FS models for serious cutting on larger or overgrown ground. Buy from a servicing dealer, learn the AutoCut head, mix fuel correctly, and keep the filter and plug fresh, and you will own a tool that reliably delivers that clean, finished edge season after season for many years.