FS 251 - Grass trimmer STIHL - Free user manual and instructions
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| Product Type | Grass Trimmer |
| Brand | STIHL |
| Model | FS 251 |
| Engine Type | 2-Stroke |
| Displacement | 27.2 cc |
| Power Output | 1.2 kW (1.6 hp) |
| Weight (without cutting attachment) | 5.5 kg |
| Cutting Path | 38 cm (15 in) |
| Fuel Tank Capacity | 0.47 L |
| Handle Type | Bike Handle |
| Drive Shaft | Straight Shaft |
| Cutting Attachment | AutoCut 25-2 |
| Vibration Level (left/right) | 5.0/3.5 m/s² |
| Sound Pressure Level | 95 dB(A) |
| Safety Features | Deflector, Throttle Lock, Stop Switch |
| Air Filter | Long-life air filter |
| Spark Plug | NGK BPMR7A or equivalent |
| Fuel/Oil Ratio | 50:1 (STIHL 2-stroke oil) |
| Spare Parts Availability | Widely available via STIHL dealers |
| Repair Service | Authorized STIHL service centers |
Frequently Asked Questions - FS 251 STIHL
What fuel mixture does the STIHL FS 251 require?
The STIHL FS 251 uses a 50:1 mixture of unleaded gasoline and STIHL two-stroke engine oil. Use only high-quality 2-stroke oil to ensure proper lubrication.
How do I start the FS 251?
Follow the starting procedure: 1) Set the master control lever to the choke position (for cold start). 2) Press the primer bulb 5-10 times. 3) Pull the starter cord until the engine starts. 4) Then move the lever to the run position. For warm starts, no choke is needed.
What is the correct cutting head line size?
The FS 251 typically uses a 2.4 mm (0.095 in) diameter trimmer line. You can also use blades such as the AutoCut 25-2 cutting head.
How do I replace the spark plug?
Use a spark plug wrench to remove the old plug. Gap the new plug to 0.5 mm (0.020 in). Recommended plug: NGK BPMR7A or equivalent. Torque to 20 Nm.
Why does my FS 251 lose power after use?
Common causes include a clogged air filter, dirty fuel filter, or incorrect fuel mixture. Clean or replace the air filter, check fuel lines, and ensure fresh 50:1 mix.
How often should I clean the air filter?
Clean the air filter every 10 hours of operation or if the engine feels sluggish. Use warm soapy water and let it dry completely before re-oiling (recommended: STIHL air filter oil).
What is the recommended maintenance schedule?
After 10 hours: clean air filter. After 50 hours: check spark plug, clean fuel filter, and inspect gearhead. After 100 hours: replace spark plug and fuel filter. Lubricate gearhead every 25 hours.
Can I use metal blades on the FS 251?
Yes, the FS 251 can be equipped with STIHL brush knives or grass blades. Ensure you use the correct deflector for blades and adjust the harness for balance.
How do I adjust the trimmer head?
To adjust the cutting height, loosen the clamp on the shaft and slide the handle to the desired position. For the cutting head, you can change the line length by tapping the head on the ground while running.
Where can I find spare parts for the FS 251?
Spare parts are available at authorized STIHL dealers and online stores. Use the model number FS 251 to ensure compatibility. Always use genuine STIHL parts for best performance.
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