Stihl FS 250 Repair Manual

The Stihl FS 250 is a professional-grade, high-power brushcutter/trimmer designed for demanding clearing and maintenance work. This manual provides comprehensive repair, maintenance, and troubleshooting information for the FS 250 engine, fuel system, ignition, cutting head, drive shaft, and gearbox. It is intended for qualified technicians. Below are key sections covering safety, specifications, disassembly, troubleshooting, and reassembly procedures.

1. Safety Precautions & Warnings 2. Technical Specifications 3. Tools & Special Equipment 4. Engine Disassembly & Assembly 5. Fuel System Repair 6. Ignition System Service 7. Drive Shaft & Gearbox 8. Cutting Attachment Service 9. Carburetor Adjustment 10. Troubleshooting Guide 11. Torque Specifications

Safety Precautions & Warnings

Before any repair, disconnect the spark plug boot to prevent accidental starting. Work in a clean, well-ventilated area. Use genuine Stihl parts. Wear appropriate personal protective equipment (PPE).

Hazard	Precaution
Fuel Fire/Explosion	Drain fuel tank before disassembly. No smoking or open flames.
Sharp Cutting Tools	Handle cutting blades and trimmer heads with heavy-duty gloves.
Spring-Loaded Components	Use caution when disassembling starter, clutch, or recoil springs.
Hot Surfaces	Allow engine and muffler to cool completely before handling.
Chemical Exposure	Use proper ventilation when handling fuel, oil, or solvents.

Technical Specifications

Model: Stihl FS 250
Engine Type: 2-MIX engine, single-cylinder, air-cooled, 2-stroke
Displacement: 41.0 cm³ (2.5 cu. in.)
Power Output: 1.6 kW (2.2 hp)
Fuel/Oil Mix: 50:1 (Stihl HP Ultra or equivalent ISO-L-EGD)
Idle Speed: 2800 rpm
Maximum Power Speed: 9000 rpm
Ignition System: Electronic, CDI
Spark Plug: Bosch WSR 6 F or equivalent, gap 0.5 mm
Drive System: Solid drive shaft, helical cut gearbox
Cutting Attachments: Accepts trimmer heads, circular metal blades, brush knives
Weight (without attachment): Approx. 6.7 kg (14.8 lbs)

Tools & Special Equipment

Standard mechanic's tools plus Stihl special tools recommended for efficient service.

Torque wrench (3-20 Nm range)
Piston stop tool (Stihl 5910 890 4500)
Flywheel puller (Stihl 5910 890 4000)
Crankcase splitting tool set
Clutch holding tool
Carburetor adjustment tool (splined)
Compression tester
Feeler gauges

WARNING! Using incorrect tools can damage components and void warranty.

Engine Disassembly & Assembly

Procedure for removing and servicing the engine block, cylinder, and piston.

Remove all external components: fuel tank, air filter, carburetor, muffler, starter.
Remove the clutch assembly using the clutch holding tool.
Remove the flywheel using the puller tool.
Split the crankcase using the splitting tool set. Note orientation of bearings and seals.
Inspect piston, rings, cylinder for scoring, wear, or carbon buildup.
Reassembly is reverse order. Apply sealant to crankcase halves as specified. Torque all fasteners to specification.

CAUTION! Mark all parts for correct reassembly. Keep work area free of debris.

Fuel System Repair

Servicing the fuel tank, lines, filter, and carburetor (likely a Zama C1Q-S series).

Fuel Line Replacement: Drain tank. Remove old lines from tank grommet and carburetor. Install new lines, ensuring they reach the bottom of the tank for the supply line.

Carburetor Rebuild: Disassemble, clean all jets, channels, and diaphragms in an ultrasonic cleaner. Inspect diaphragms for stiffness or tears. Replace gaskets and diaphragms with a rebuild kit. Reinstall and adjust.

Ignition System Service

Testing and replacing the ignition coil, spark plug, and stop switch.

Spark Test: Remove spark plug, reconnect boot, ground plug against cylinder. Pull starter rope. Look for strong blue spark.
Coil Resistance Test: Use multimeter. Primary winding: ~0.5-2.0 Ω. Secondary winding: ~5-20 kΩ. Replace if out of spec or if spark is weak.
Stop Switch Test: Disconnect wire from coil. Test for continuity between switch wire and ground when switch is pressed. Should show continuity.

Tip: Always start diagnosis with a fresh, properly gapped spark plug.

Drive Shaft & Gearbox

Service for the solid drive shaft and helical gear head.

Remove the cutting attachment and drive shaft cover.
Disconnect the shaft from the engine clutch drum.
Inspect shaft for straightness and spline wear.
For gearbox: Remove gear head housing. Check gears for chipping or excessive wear. Check seals for leaks. Repack with Stihl gear grease.
Reassemble, ensuring seals are properly seated to prevent grease leakage.

WARNING! A bent drive shaft causes severe vibration and must be replaced.

Cutting Attachment Service

Maintenance for trimmer heads and metal blades.

Trimmer Head (AutoCut C 6-2): Replace worn cutting line. To replace spool, depress tabs, remove cover, wind new line following directional arrows. Ensure line lengths are equal.

Metal Blades: Check for cracks, nicks, or imbalance. Sharpen with a file, maintaining original angle. Always use the correct blade washer and retaining nut. Tighten nut to specified torque.

Carburetor Adjustment

Final adjustment after rebuild or for performance issues. Engine must be at operating temperature.

L (Low Speed) Jet: Turn in until lightly seated, then open 1 turn as a baseline.
H (High Speed) Jet: Turn in until lightly seated, then open 1 turn as a baseline.
LA (Idle Speed) Screw: Adjust to achieve a steady 2800 rpm idle.
Fine Tuning: Run at full throttle. Adjust H jet for maximum RPM without "lean bog" (surging). Adjust L jet for smooth acceleration from idle. Readjust idle speed if necessary.

CAUTION! A lean mixture (too little fuel) causes engine overheating and severe damage.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, fuel, or compression	Check spark, fuel delivery, and compression (should be >100 psi).
Engine starts then dies	Clogged fuel filter, bad diaphragm, air leak	Replace fuel filter, rebuild carb, check crankcase seals & intake boot.
Loss of power	Clogged air filter, exhaust screen, carb adjustment	Clean/replace air filter, clean spark arrestor screen, adjust carb.
Excessive vibration	Bent drive shaft, unbalanced blade, loose parts	Inspect shaft, check blade balance, tighten all fasteners.
Gearbox overheating/leaking	Low grease, damaged seal, worn gears	Disassemble gear head, replace seals/gears, repack with grease.

Compression Test: Reading below 90 psi indicates worn piston/rings or cylinder damage.

Torque Specifications

Critical fastener torque values. Use a calibrated torque wrench.

Component	Torque (Nm)	Torque (lb-in / lb-ft)
Crankcase Screws	10 Nm	88 lb-in
Cylinder Nuts	20 Nm	15 lb-ft
Clutch Nut	40 Nm	30 lb-ft
Flywheel Nut	50 Nm	37 lb-ft
Spark Plug	25 Nm	18 lb-ft
Gearhead Retaining Nut	60 Nm	44 lb-ft
Blade Retaining Nut	40 Nm	30 lb-ft

Service: For technical support or genuine parts, contact your authorized Stihl dealer.