Introduction
The Stihl FS45 is a lightweight, gasoline‑powered string trimmer that many homeowners and landscaping professionals rely on for clean edges and quick weed removal. Knowing how to start Stihl Fs45 Weed Eater correctly saves time, reduces wear on the engine, and keeps the operator safe. This guide walks you through every phase of the starting process, from pre‑start checks to troubleshooting a stubborn engine, and it includes maintenance habits that make future starts effortless.
- Understanding the Stihl FS45
- Safety Precautions Before Starting
- Required Tools and Materials
- Step‑by‑Step Starting Procedure
- Cold Start vs Warm Start Differences
- Troubleshooting Common Starting Issues
- Maintenance Tips for Reliable Starts
- Comparison Table: FS45 vs Other Stihl Trimmers
- Best Practices for Longevity
- Common Mistakes to Avoid
- Frequently Asked Questions
- Conclusion
Understanding the Stihl FS45
The FS45 belongs to Stihl’s entry‑level professional line. It features a 27.2 cc two‑stroke engine that delivers a respectable 1.1 kW of power while keeping the overall weight around 4.6 kg (10.1 lb). The trimmer uses a semi‑automatic choke system, a primer bulb, and a recoil starter. Because the engine is air‑cooled and runs on a 50:1 fuel‑oil mixture, proper fuel preparation is essential for reliable ignition. The cutting head accepts a variety of nylon line diameters, and the shaft is designed for comfortable, balanced handling during extended use.
One of the FS45’s design goals is quick, repeatable starts. The choke lever, primer bulb, and throttle trigger are positioned so the operator can reach them without shifting grip. Understanding each component’s role helps you follow the start sequence without guesswork.
Safety Precautions Before Starting
Before you even think about pulling the starter rope, make sure the work area is clear of bystanders, pets, and flammable materials. Wear eye protection, hearing protection, sturdy gloves, long pants, and closed‑toe boots. Verify that the trimmer’s guard is securely attached and that the cutting line is not damaged or excessively worn. Never start the engine in an enclosed space; carbon monoxide builds up quickly and can be fatal.
Check the fuel tank for the correct 50:1 mixture. Using straight gasoline or an incorrect ratio can cause hard starting, excessive smoke, or engine damage. Confirm that the fuel cap vents properly; a blocked vent creates vacuum lock and prevents fuel flow. Finally, ensure the spark plug boot is firmly seated and that the spark plug gap matches the manufacturer’s specification (typically 0.5 mm).
Required Tools and Materials
Having the right items on hand eliminates interruptions during the start routine. The essential list includes:
- Fresh 50:1 pre‑mixed fuel or separate gasoline and two‑stroke oil for mixing
- Clean container for fuel mixing
- Spark plug socket (usually 13 mm) and gap gauge
- Small brush or compressed air for cleaning the air filter
- Protective gear as described in the safety section
- Owner’s manual for reference to torque specs and part numbers
Optional but helpful tools are a fuel stabilizer for seasonal storage, a spare spark plug, and a torque wrench for precise reinstallation of the spark plug.
Step‑by‑Step Starting Procedure
Follow these steps each time you need to start the FS45. The sequence works for both cold and warm engines; the only difference is choke position, which is covered in the next section.
- Place the trimmer on a flat, stable surface. Keep the cutting head away from your body and any obstacles.
- Set the choke lever to the “Full Choke” position. On a cold engine this enriches the mixture for easier ignition.
- Press the primer bulb 5–7 times. You should see fuel moving through the clear fuel line; this primes the carburetor.
- Engage the throttle trigger to the “Start” detent. This holds the throttle slightly open, providing the engine with enough air‑fuel mix to fire.
- Grip the starter handle firmly and pull the rope briskly. Use a smooth, full‑length pull; avoid yanking. The engine should cough and then run.
- Once the engine fires, immediately move the choke lever to the “Half Choke” position. This leans the mixture as the engine warms.
- Allow the engine to run for 10–15 seconds. Then move the choke to the “Run” (off) position.
- Release the throttle trigger to the idle position. The trimmer should now idle smoothly.
- Test the cutting head. Squeeze the throttle gently; the line should spin freely. If it stalls, repeat the choke adjustment.
If the engine does not start after three pulls, return the choke to “Full Choke,” re‑prime, and try again. Persistent failure indicates a deeper issue covered in the troubleshooting section.
Cold Start vs Warm Start Differences
A cold start requires the full choke and several primer pumps because the fuel in the carburetor has evaporated and the engine block is cold. A warm start—typically within 10–15 minutes of a previous run—needs only the half‑choke or even the run position, and often just one or two primer presses. The throttle trigger should still be set to the start detent for both scenarios. Skipping the choke adjustment on a cold engine leads to flooding, while using full choke on a warm engine causes rough running and excess smoke.
Recognizing engine temperature by feel (the cylinder head will be warm to the touch after a recent run) helps you choose the correct choke setting without guesswork.
Troubleshooting Common Starting Issues
Even a well‑maintained FS45 can refuse to start. The table below lists frequent symptoms, likely causes, and corrective actions.
| Symptom | Probable Cause | Fix |
|---|---|---|
| Engine cranks but never fires | Stale or incorrect fuel mixture | Drain tank, refill with fresh 50:1 mix |
| Engine fires then dies immediately | Choke left in full position too long | Move choke to half then run promptly |
| Hard pull, rope feels stiff | Flooded cylinder | Remove spark plug, pull rope to clear excess fuel, reinstall plug |
| No spark at plug | Fouled or damaged spark plug | Clean or replace plug, check gap |
| Primer bulb stays collapsed | Clogged fuel line or filter | Inspect and clean fuel line, replace filter |
If none of these remedies restore reliable starting, consult a certified Stihl dealer for carburetor cleaning or ignition module testing.
Maintenance Tips for Reliable Starts
Regular upkeep is the single biggest factor in consistent starts. Perform the following at the intervals suggested in the owner’s manual:
- Air filter: Clean or replace every 25 hours of operation. A clogged filter starves the engine of air.
- Spark plug: Inspect every 50 hours; replace annually or if the electrode is worn.
- Fuel system: Drain old fuel before long storage; add stabilizer if the trimmer will sit more than 30 days.
- Cutting head: Check line wear and replace the spool when the line diameter drops below 2.4 mm.
- Recoil starter: Lubricate the spring lightly with a few drops of light machine oil once per season.
Keeping a maintenance log helps you track intervals and spot patterns that precede starting problems.
Comparison Table: FS45 vs Other Stihl Trimmers
Choosing the right trimmer often comes down to power, weight, and starting system. The table below highlights key differences among popular Stihl models.
| Model | Engine Displacement (cc) | Power (kW) | Weight (kg) | Starting System | Best Use Case |
|---|---|---|---|---|---|
| FS45 | 27.2 | 1.1 | 4.6 | Recoil + Primer + Choke | Residential lawns, light commercial |
| FS55 | 27.2 | 1.2 | 4.9 | Recoil + Primer + Choke | Larger yards, thicker weeds |
| FS70 | 27.2 | 1.3 | 5.2 | Recoil + Primer + Choke | Professional landscaping |
| FS90 | 28.4 | 1.5 | 5.8 | Recoil + Primer + Choke | Heavy‑duty brush clearing |
The FS45 remains the lightest and most maneuverable, making it ideal for users who prioritize ease of handling over raw power.
Best Practices for Longevity
Adopting a few habits extends the life of your FS45 and keeps starts effortless:
- Always use fresh, correctly mixed fuel; avoid gasoline older than 30 days.
- Run the engine at idle for a minute before shutting off to clear residual fuel from the carburetor.
- Store the trimmer upright in a dry, ventilated area; keep the fuel tank at least 50 % full to minimize condensation.
- Inspect the spark plug boot for cracks each season; replace if brittle.
- Sharpen or replace the cutting line before it becomes too short; a worn line forces the engine to work harder.
These practices reduce carbon buildup, prevent gummed carburetors, and keep the recoil mechanism smooth.
Common Mistakes to Avoid
Even experienced users sometimes slip into habits that cause hard starts or damage:
- Over‑priming: More than 7 presses floods the carburetor, leading to a wet spark plug.
- Leaving the choke on: Running with full choke after the engine fires creates carbon deposits and wastes fuel.
- Using the wrong fuel ratio: A richer mixture (e.g., 40:1) fouls the plug; a leaner mix (e.g., 60:1) overheats the piston.
- Pulling the starter rope at an angle: This stresses the recoil spring and can snap the rope.
- Neglecting the air filter: A dirty filter mimics fuel problems and leads to unnecessary carburetor adjustments.
Correcting these behaviors early saves time and money on repairs.
Frequently Asked Questions
How many times should I press the primer bulb on a cold start?
Press the primer bulb 5 to 7 times until you see fuel moving through the clear line. Over‑priming can flood the engine, while under‑priming may leave the carburetor dry.
What fuel mixture does the Stihl FS45 require?
The FS45 runs on a 50:1 ratio of unleaded gasoline to two‑stroke engine oil. Use a high‑quality synthetic or semi‑synthetic oil labeled for air‑cooled two‑stroke engines.
Why does my trimmer start but then die after a few seconds?
This usually means the choke was left in the full position too long. Move the choke to half choke as soon as the engine fires, then to run after 10–15 seconds.
Can I use ethanol‑blended gasoline in the FS45?
Stihl recommends gasoline with no more than 10 % ethanol (E10). Higher ethanol blends attract moisture and can cause phase separation, leading to starting problems.
How often should I replace the spark plug?
Inspect the spark plug every 50 hours of operation and replace it at least once per season, or sooner if the electrode shows excessive wear or fouling.
Conclusion
Starting the Stihl FS45 reliably comes down to a disciplined routine: verify fuel quality, set the choke correctly, prime the carburetor, and pull the starter with a smooth motion. By following the step‑by‑step procedure outlined above, respecting cold‑ versus warm‑start differences, and keeping up with basic maintenance, you’ll enjoy quick starts every time you reach for the trimmer. Avoid common pitfalls such as over‑priming or leaving the choke engaged, and consult the troubleshooting table when the engine behaves unexpectedly. With these habits in place, the FS45 will remain a dependable tool for clean edges and weed‑free beds season after season.