Stihl FS 310 Manual

The Stihl FS 310 is a professional-grade, high-power brushcutter/string trimmer designed for demanding clearing and maintenance work. It features a powerful 2-stroke engine with electronic ignition, anti-vibration system, loop handle with integrated controls, straight shaft, harness attachment points, and compatibility with a wide range of cutting attachments. Below are key sections for safety, features, operation, maintenance, and troubleshooting.

1. Features at a Glance 2. Safety Instructions 3. Assembly & Preparation 4. Specifications 5. Controls and Operation 6. Fuel & Lubrication 7. Cutting Attachments 8. Maintenance Schedule 9. Storage 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: Powerful 2-stroke engine, Straight drive shaft, Loop handle with master control lever, Anti-vibration system, QuickStop inertia chain brake (if equipped with cutting blade), and attachment points for harness.

Feature	Description
Engine Type	2-stroke, single-cylinder, air-cooled
Ignition System	Electronic ignition (CDI)
Fuel Tank Capacity	Approx. 0.95 liters (1.0 US qt)
Drive Shaft	Solid, straight shaft
Anti-Vibration	Integrated dampening elements in handle and shaft
Handle System	Loop handle with integrated controls
Cutting Attachment	Accepts trimmer heads, metal blades, brush knives
Starter	Rewind starter with decompression valve
Weight (without attachment)	Approx. 7.5 kg (16.5 lbs)
Sound Power Level	High - hearing protection required

Safety Instructions

Read and understand the manual before operation. Always wear appropriate PPE.

Personal Protective Equipment (PPE): Always wear safety glasses, hearing protection, heavy-duty gloves, long pants, sturdy boots, and a hard hat when clearing overhead.
Operation Area: Keep bystanders, children, and pets at least 15 meters away. Clear the work area of debris like stones and wire.
Fuel Safety: Refuel outdoors only, with engine stopped and cool. Use only STIHL MotoMix or a 50:1 mixture of high-quality 2-stroke oil and unleaded gasoline (min. 89 octane).
Starting & Carrying: Start on the ground, firmly holding the unit. Do not drop-start. Carry unit with the cutting attachment stopped and pointed away.
Kickback Danger: Be aware of kickback, especially when using metal cutting blades. The cutting attachment rotates counter-clockwise.

WARNING! Improper use can cause serious or fatal injury. Never operate with a damaged or missing guard.

Assembly & Preparation

Unpack and inspect all parts. Assemble on a clean, stable surface.

Handle Attachment: Slide the loop handle onto the shaft at the desired position and tighten the clamping screws securely.
Harness Attachment: Connect the harness rings to the attachment points on the rear of the machine.
Cutting Attachment: Ensure the engine is off. Fit the chosen trimmer head or blade, securing it with the appropriate nut and washer. Use the shaft lock to hold the shaft while tightening.
Fuel Mix: Fill the fuel tank with the correct 50:1 fuel/oil mixture. Fill the separate chain oil tank (if using a saw blade attachment) with STIHL chain oil.

CAUTION! Ensure all fasteners are tight before starting. A loose cutting attachment can be violently thrown.

Specifications

Engine Displacement: 56.5 cc
Power Output: High performance professional engine
Idle Speed: 2,800 rpm (factory set)
Maximum Powerhead Speed: 7,500 rpm
Recommended Cutting Attachments: STIHL AutoCut trimmer heads, circular saw blades, brush knives, grass blades
Drive System:Direct drive via rigid shaft and gearhead
Vibration Levels: Front/Rear handle: Typically < 2.5 m/s²

Emissions Compliance: Meets EPA Phase II and CARB regulations

Warranty: Limited commercial warranty (see dealer for details)

Controls and Operation

Master Control Lever: Located on the handle. Must be held in against the handle to allow the engine to run. Releases to stop the engine.

Throttle Trigger: Located inside the handle. Controls engine speed.

Throttle Trigger Lockout: Must be depressed before the throttle trigger can be engaged.

Stop Switch: Move to "0" or "STOP" to shut off the engine.

Choke/Start Aid Lever: Used for cold starting.

Decompression Valve: Reduces pulling force for the starter.

Starting Procedure (Cold): 1. Press the fuel primer bulb 5-10 times. 2. Set the choke lever to full choke (up position). 3. Lock the throttle trigger by pressing the lockout and squeezing the trigger, then push the master control lever in and hold. 4. Place unit on firm ground, hold securely. 5. Pull starter rope briskly until engine fires (usually 1-3 pulls). 6. Immediately move choke lever to half-choke position. 7. Pull starter rope again to start. Once running, briefly blip the throttle to move choke to run position.

Fuel & Lubrication

Fuel Mixture: Use only high-quality unleaded gasoline (min. 89 octane) mixed with a high-performance 2-stroke engine oil at a 50:1 ratio. STIHL MotoMix pre-mixed fuel is recommended to ensure optimal performance and avoid fuel-related issues.

Mixing Instructions: Add oil to an approved fuel can first, then add gasoline. Close can and shake thoroughly.

Gearhead Lubrication: The gearhead is filled with grease at the factory. Periodically check for leakage and re-grease using STIHL gear grease as described in the maintenance section.

Air Filter: Clean regularly (every 10 operating hours) with compressed air or by tapping out debris. Replace if damaged or excessively dirty.

Spark Plug: Use STIHL recommended type (e.g., BOSCH WSR6F). Check gap (0.020 in / 0.5 mm) and clean every 50 hours. Replace annually or as needed.

Cutting Attachments

The FS 310 is compatible with a wide range of attachments via its standard drive square.

Trimmer Heads (e.g., AutoCut): For grass and light weeds. Ensure the correct line diameter is used and the line is not too long.

Circular Metal Blades: For thick weeds, brush, and saplings. Always use the correct guard and harness. Be extremely mindful of kickback.

Brush Knives: 3-tooth or 8-tooth knives for heavy brush clearing.

Grass Blades: Multi-tooth blades for dense grass.

WARNING! Always use the correct guard for the attachment. Never use a trimmer head guard with a metal blade. Ensure the attachment is properly seated and the retaining nut is securely tightened with the shaft locked.

Maintenance Schedule

Interval Task

Before each use Check for loose fasteners, damaged parts, and proper guard installation. Check fuel level.

Daily (or every 10 hrs) Clean air filter. Check cutting attachment for damage and tightness.

Every 50 hours Clean spark plug, check electrode gap. Clean cooling fins. Check gearhead for grease leakage.

Every 100 hours Replace spark plug. Clean fuel filter in tank. Grease gearhead (remove old grease and refill).

Annually or as needed Have a STIHL authorized dealer check carburetor adjustment, compression, and overall condition.

CAUTION! All maintenance should be performed with the engine OFF and cool. Disconnect the spark plug boot for safety during major work.

Storage

For storage longer than 30 days, prepare the unit to prevent fuel system damage.

Run the engine to empty the carburetor of fuel, or add fuel stabilizer to a full tank and run for 2 minutes.

Allow engine to cool completely.

Thoroughly clean the entire unit, removing all dirt, debris, and plant sap.

Remove the cutting attachment. Lightly oil the drive square and attachment interface.

Store in a dry, well-ventilated place, out of reach of children. Cover the unit to keep dust off.

WARNING! Never store the unit with fuel in the tank indoors or in an enclosed space where fuel vapors could accumulate.

Regulatory Information

This product complies with all relevant U.S. emission and safety standards. The engine exhaust from this product contains chemicals known to the State of California to cause cancer, birth defects, or other reproductive harm. STIHL and the STIHL logo are registered trademarks of Andreas Stihl AG & Co. KG. For genuine parts, accessories, and service, contact an authorized STIHL servicing dealer. For support, visit www.stihlusa.com or contact customer service at 1-800-467-8445.

Troubleshooting

Symptom Possible Cause Corrective Action

Engine will not start No fuel, flooded, bad spark, choke position wrong Check fuel. If flooded, move choke to run, hold throttle wide open, and pull starter. Check spark plug.

Engine starts but dies Clogged fuel filter, dirty air filter, carburetor adjustment Clean/replace fuel filter. Clean air filter. Have dealer check carburetor.

Loss of power Clogged air filter, dirty spark arrestor screen, old fuel Clean air filter. Clean spark arrestor screen (muffler). Use fresh fuel mix.

Excessive vibration Bent cutting attachment, loose fasteners, damaged drive shaft Stop engine. Check attachment for damage/balance. Tighten all fasteners. Inspect shaft.

Cutting attachment does not spin Sheared drive pin (if equipped), damaged gearhead Stop engine. Check and replace shear pin. If gearhead is damaged, see dealer.

Gearhead overheats or leaks grease Insufficient grease, damaged seals Clean and re-grease gearhead. If seals are damaged, replace gearhead or see dealer.

Dealer Service: For repairs beyond basic maintenance, take the unit to an authorized STIHL dealer.

Customer Support: 1-800-467-8445; www.stihlusa.com

Stihl FS 310 Manual © - All Rights Reserved 2025

Interval	Task
Before each use	Check for loose fasteners, damaged parts, and proper guard installation. Check fuel level.
Daily (or every 10 hrs)	Clean air filter. Check cutting attachment for damage and tightness.
Every 50 hours	Clean spark plug, check electrode gap. Clean cooling fins. Check gearhead for grease leakage.
Every 100 hours	Replace spark plug. Clean fuel filter in tank. Grease gearhead (remove old grease and refill).
Annually or as needed	Have a STIHL authorized dealer check carburetor adjustment, compression, and overall condition.

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, bad spark, choke position wrong	Check fuel. If flooded, move choke to run, hold throttle wide open, and pull starter. Check spark plug.
Engine starts but dies	Clogged fuel filter, dirty air filter, carburetor adjustment	Clean/replace fuel filter. Clean air filter. Have dealer check carburetor.
Loss of power	Clogged air filter, dirty spark arrestor screen, old fuel	Clean air filter. Clean spark arrestor screen (muffler). Use fresh fuel mix.
Excessive vibration	Bent cutting attachment, loose fasteners, damaged drive shaft	Stop engine. Check attachment for damage/balance. Tighten all fasteners. Inspect shaft.
Cutting attachment does not spin	Sheared drive pin (if equipped), damaged gearhead	Stop engine. Check and replace shear pin. If gearhead is damaged, see dealer.
Gearhead overheats or leaks grease	Insufficient grease, damaged seals	Clean and re-grease gearhead. If seals are damaged, replace gearhead or see dealer.