Stihl FS 85 vs. FS 106 Trimmer (Field Test)

The FS 85 is documented as a 25.4 cm³ two-stroke brushcutter with commonly listed output of 0.95 kW (1.3 hp). I can’t verify matching specifications for every FS 106 version, so a fair comparison starts with its nameplate and exact manual. Choose by condition, approved attachments, and safe performance, not an assumed power advantage.

When an older trimmer starts poorly or bogs in thick growth, it is tempting to replace it with the model that sounds stronger. But the FS 85 and FS 106 are older machines, and model details can vary by market or version. A model number alone cannot confirm the right fuel ratio, cutting attachment, or operating limits.

I would not call a comparison a measured field test without two identified machines and recorded results. The FS 85 figures below are available specifications; the FS 106 details must be checked on the actual machine. That distinction matters: it prevents a guess from turning into an unsafe setup or an expensive repair.

What the FS 85 and FS 106 Comparison Can Establish

This comparison separates confirmed information from details that need checking on your specific trimmer. It can help you assess engine size, condition, and suitable work, but it cannot establish that one model cuts faster or lasts longer without verified FS 106 data and comparable test results.

Displacement is the engine’s cylinder volume, measured in cubic centimetres (cm³). It does not, by itself, prove that a machine will cut faster. A worn engine, wrong head, damaged line, dull blade, or poor tuning can matter as much as the model name.

For the FS 85, 25.4 cm³ and 0.95 kW (1.3 hp) are commonly listed figures, but verify that they match your market and version. For the FS 106, use its nameplate and the STIHL manual that matches the model and serial-number version. If a seller quotes power, tank size, or maximum RPM, ask for the source rather than treating it as universal.

Before comparing either trimmer, inspect both in similar condition. A test between a serviced FS 85 and a neglected FS 106 would measure maintenance more than model performance.

Equipment Setup and Safety Preparation

A fair comparison begins with two safe, correctly identified machines and the right equipment fitted to each. Check the model and manual first, then inspect the guard, handle, harness, cutting tool, fuel system, and stop control. Do not start a trial until the setup is approved and secure.

Find the model plate and record the full model identification. Match it to the correct instruction manual, including any version details the manual requires. Manuals can specify different cutting heads, blade sizes, guards, handles, harnesses, and fuel instructions. Do not transfer an FS 85 setup to an FS 106 just because the machines look alike.

Before starting, check:

• The guard is present, secure, and correct for the attachment.
• The cutting head or blade is approved for that exact model version.
• The handle, harness, and attachment fasteners are secure.
• The fuel lines and tank show no leak or damage.
• The stop control works, and the cutting attachment does not turn at idle.
• Eye or face protection, hearing protection, gloves, long trousers, and sturdy boots are in use.

Clear people and pets from the work area. Look for stones, wire, glass, fencing, and other hidden hazards. A metal blade can react sharply if it hits a rigid object or catches wire. Use only its specified guard and compatible handle and harness setup, and follow the manual’s blade technique. Never remove the guard to make a tool fit.

For fuel, follow the manual supplied for the specific machine. STIHL’s current general recommendation for compatible two-stroke equipment is a 50:1 mix with STIHL two-stroke oil. Older manuals or market-specific instructions can differ, so do not assume that ratio applies to every FS 85 or FS 106. Never run either machine on straight gasoline or an unverified mix.

Field Trimming and Brushcutting Operation

A useful field comparison tests the machines on the same vegetation with approved, comparable attachments and a repeatable method. Since FS 106 specifications and attachment limits are not confirmed here, this is a test procedure, not a claim that one model has already beaten the other in measured trials.

Choose a clear area with vegetation that matches the job you expect to do. Do not begin in dense brush if you have not confirmed that the installed tool is approved for it. Set both machines up according to their own manuals; record the attachment type and line or blade condition before cutting.

Use the same area and work in short, timed sections. Note how each machine starts, idles, cuts, and responds under ordinary load. Record fuel used only if you can measure it consistently and safely. Stop if either machine overheats, vibrates abnormally, leaks fuel, stalls repeatedly, or fails to idle without turning the attachment.

Keep the head or blade below waist level and away from your body. Use controlled sweeps. Do not force the tool into thick growth or strike rocks, fences, or hard stems. Stop the engine before clearing tangled grass, checking a fastener, or adjusting the attachment.

Field-fit example: routine grass and weeds. If both machines have sound engines and approved line heads, compare starting, balance, and cutting progress on the same patch. A worn or incorrectly loaded line head can distort the result, so use the specified line and loading method for each model.

Field-fit example: woody growth. Do not assume either model can safely take a metal blade. Confirm the allowed blade, diameter, guard, handle, and harness in that machine’s manual. If those details cannot be verified, use an approved line head within its limits or choose equipment designed for the task.

These are practical test scenarios, not reports of measured performance. A real result needs the exact FS 106 version, matched setups, and recorded observations. The safer takeaway is simple: attachment limits and machine condition come before a head-to-head power claim.

Maintenance, Inspection, and Carburetor Tuning

A carburetor meters fuel and air for the engine. Poor starting or stalling can have several causes, so do not begin by turning adjustment screws. Check fuel, air flow, the plug, and basic condition first; use the exact manual specifications for any carburetor adjustment.

Use fresh fuel mixed at the ratio in the correct manual. If the machine has been stored with fuel in it, old fuel may contribute to hard starting or rough running. Drain or handle fuel as directed by the manual and local rules; do not pour it onto the ground or into a drain.

A practical first check is:

• Inspect the air filter and clean or replace it as the manual directs.
• Check the spark plug for damage or heavy deposits; use the specified type and gap.
• Inspect the fuel lines, tank, and filter for damage or blockage.
• Check the cutting attachment for entangled grass, damage, or loose parts, with the engine stopped.
• Confirm the guard and fasteners are intact before restarting.

If the engine still runs poorly, seek service or follow the model’s exact carburetor procedure. Do not tune idle or maximum speed from generic online RPM figures. A tachometer and the correct manual procedure may be required. Incorrect mixture or overspeed can damage the engine; stop work if the attachment turns at idle or the engine races.

For a comparison, record repairs and adjustments on each machine. A carburetor problem on one unit does not show that the other model is inherently more reliable. Likewise, fresh fuel and a clean filter can change a field result substantially.

Storage and Seasonal Care

Good storage reduces the chance that either trimmer will be hard to start next season. Follow the manual’s fuel-storage instructions, clean debris after use, and keep the machine dry and secure. Do not store it with an unverified fuel mix or an attachment that is damaged or loose.

After work, stop the engine and let hot parts cool. Check the cutting tool, guard, fasteners, and air intake for damage or packed debris. Remove grass only after the engine is off, and do not handle a hot muffler or cutting attachment.

Before seasonal storage, use the manual’s directions for fuel and engine care. Procedures can differ, so avoid applying one model’s storage steps to the other without checking. Store fuel in an approved container, away from heat or ignition sources, and follow its label and local safety rules.

When taking a trimmer out of storage, inspect it before starting. Check fuel lines, the stop control, guard, attachment, and harness. Start on stable ground with the cutting tool clear of people and objects. If it leaks, vibrates abnormally, or will not idle safely, stop and repair it before use.

Which Trimmer Should You Choose?

The better choice is the machine whose identity, condition, and approved setup you can verify. The FS 85 has a commonly listed 25.4 cm³ engine and 0.95 kW (1.3 hp) output. For the FS 106, confirm specifications from its own nameplate and matching manual before comparing power, fuel use, or attachments.

If both machines are available to inspect, check cold starting, idle stability, throttle response, vibration, and service condition. Compare them with their manuals and equivalent approved cutting setups. Do not choose by a claimed engine advantage that cannot be traced to a reliable specification.

For a purchase, ask the seller for the manual, service history, and a cold start. For a machine you already own, identify the version before ordering a blade, guard, or carburetor part. If the nameplate or manual is missing, a STIHL dealer may be able to help identify compatible parts and instructions.

Frequently Asked Questions

These answers focus on what can be confirmed safely without guessing at an FS 106 specification. Check the nameplate and exact manual for machine-specific limits, fuel instructions, and approved attachments.

Is the FS 85 more powerful than the FS 106?

The FS 85 is commonly listed at 0.95 kW (1.3 hp). I can’t verify a matching FS 106 power figure here, so there is not enough confirmed information to say which is more powerful.

What is the FS 85 engine size?

The FS 85 is commonly listed with 25.4 cm³ displacement. Verify the figure against the manual for your market and machine version.

What is the FS 106 engine size?

Its displacement is not confirmed here. Read the nameplate and consult the manual that matches the exact FS 106 version.

Can I use the same cutting attachment on both?

Only if each machine’s manual approves that attachment and its guard and setup. Similar appearance does not establish compatibility.

Should I use a 50:1 fuel mix?

Use the ratio in the specific machine’s manual. STIHL’s current general recommendation for compatible two-stroke equipment is 50:1 with STIHL two-stroke oil, but an older or market-specific manual may differ.

Why does the cutting head spin at idle?

That is a stop-and-check condition. Stop the engine and follow the manual’s idle and carburetor guidance, or have a qualified service shop inspect it. Do not continue operating while the attachment turns at idle.

Can I fit a metal blade to either model?

Do so only when the exact manual approves the blade and specifies the matching guard, handle, and harness arrangement. If you cannot confirm the setup, do not install the blade.

What should I check first if either trimmer will not start?

Check the manual’s starting steps, fresh correctly mixed fuel, air filter, spark plug, and fuel-system condition. If it still fails to start, avoid random carburetor adjustments and seek model-specific service guidance.

(This article was written by one of our staff writers, Harrison Croft. Visit our Meet the Team page.)