Get your Stihl FS 45 string trimmer back to reliable cutting performance with genuine OEM replacement parts from Repair Clinic. The FS 45 is a residential-class straight-shaft trimmer using a two-stroke engine that runs on a premixed gasoline-and-two-stroke-oil fuel blend. The primer bulb on the FS 45 supplies fuel directly to the carburetor for easier cold starting; a cracked or leaking primer bulb prevents this priming function and contributes to hard-starting complaints. Parts most frequently replaced include the carburetor, spark plug, air filter, cutting line, and primer bulb. Use the FS 45 parts list and browse the full Stihl trimmer parts catalog.
Stihl FS 45 Residential Platform: Primer Bulb Function and Trimmer Head Line-Winding Technique
The Stihl FS 45 primer bulb is a flexible rubber component that, when pressed, draws fuel from the tank into the carburetor before starting, improving cold-start reliability on this two-stroke engine. A primer bulb that is cracked, hardened, or does not return to its original shape after being pressed has failed and no longer performs this priming function effectively, contributing to hard-starting complaints that can otherwise be mistaken for carburetor problems. The FS 45 trimmer head uses a manual line-winding spool system rather than an automatic feed; even winding of the cutting line on the spool is necessary for the line to feed correctly and avoid jamming inside the head housing. For repair guidance, visit the Stihl trimmer repair help section.
FS 45 Component Failures and Service Procedures
Stihl FS 45 Primer Bulb Failure and Hard-Starting Diagnosis
A FS 45 that requires excessive pulls to start, particularly when cold, may have a cracked or hardened primer bulb that no longer draws adequate fuel into the carburetor during priming. Inspect the bulb for cracks and confirm it returns fully to shape after being pressed; a bulb that stays compressed or shows visible cracking has failed and should be replaced before assuming a carburetor fault.
FS 45 Cutting Line Winding and Spool Feed Technique
Uneven winding of cutting line on the FS 45 spool causes the line to bind or jam inside the trimmer head housing rather than feeding smoothly. When replacing the cutting line, wind it evenly in the direction indicated on the spool, keeping consistent tension throughout to prevent overlapping coils that catch during feed.
FS 45 Carburetor Varnish and Post-Storage Starting Failure
The FS 45 carburetor is the primary diagnostic target for any trimmer that fails to start after off-season storage. Ethanol-blend fuel deposits varnish on the diaphragm passages during storage. Drain the fuel system before storage each winter. Browse Stihl trimmer carburetor parts.
FS 45 Spark Plug Service and Annual Replacement
Replace the FS 45 spark plug every 100 hours of operation or annually, whichever comes first. A worn plug causes difficulty starting and inconsistent engine performance, including misfiring under load.
Stihl FS 45 Parts at Repair Clinic
- Genuine Stihl OEM Parts for the FS 45 Residential Platform: Every FS 45 part meets Stihl OEM specifications. Browse the full Stihl trimmer parts catalog.
- Primer Bulb Diagnostic Clarity: Our content documents the primer bulb inspection that should precede carburetor replacement for hard-starting complaints, since a failed bulb produces similar symptoms.
- Line-Winding Technique Guidance: Our content documents correct manual line-winding technique to prevent jamming inside the FS 45 trimmer head.
- 365-Day Returns and Fast Shipping: All FS 45 parts ship promptly. The Stihl trimmer repair help section provides step-by-step guidance.
Stihl FS 45 String Trimmer Parts FAQ
Why does my Stihl FS 45 need many pulls to start when cold?
A FS 45 that requires excessive pulls to start, particularly in cold conditions, may have a cracked or hardened primer bulb that no longer draws adequate fuel into the carburetor during priming. Inspect the bulb for visible cracks and confirm it returns fully to its original shape after being pressed; a bulb that fails this check should be replaced before assuming the carburetor itself has failed.
How do I wind the cutting line correctly on my FS 45?
Wind the replacement cutting line evenly onto the FS 45 spool in the direction indicated by the arrow molded into the spool body, maintaining consistent tension throughout the winding process. Uneven winding with overlapping coils causes the line to bind or jam inside the trimmer head housing during operation rather than feeding smoothly when bumped.
How often should I replace the spark plug on my FS 45?
Replace the Stihl FS 45 spark plug every 100 hours of operation or once per trimming season, whichever comes first. A worn spark plug causes difficulty starting, rough idle, and misfiring under cutting load; replacing it on this schedule maintains reliable performance throughout the season.
What causes the FS 45 to vibrate excessively during operation?
Excessive vibration on the FS 45 most commonly results from an unbalanced trimmer head, loose engine mounting hardware, or worn internal cutting head components. Inspect the trimmer head for damage or uneven line winding first, then confirm all mounting bolts and fasteners are properly tightened before investigating more involved engine or shaft components.
