STIHL FS 90 Trimmer Parts Manual

The STIHL FS 90 is a professional-grade gasoline-powered trimmer designed for demanding clearing and trimming tasks. This parts manual provides detailed exploded views, part numbers, and descriptions for all components of the FS 90 trimmer, including the engine, drive shaft, cutting head, handles, and fuel system. It is intended for authorized service technicians and experienced users to assist in maintenance, repair, and ordering of genuine STIHL replacement parts. Below are key sections for identification, engine parts, drive train, cutting attachments, and ordering information.

1. Introduction & Model Identification 2. Engine Assembly Parts 3. Drive Shaft & Gearbox Parts 4. Cutting Attachment Parts 5. Handle & Control Parts 6. Fuel System Parts 7. Air Filter & Exhaust System 8. Ignition System Parts 9. Starter Assembly Parts 10. Fasteners & Miscellaneous Parts 11. Parts Ordering & Diagrams

Introduction & Model Identification

Key identifiers: The STIHL FS 90 is a straight-shaft trimmer. Locate the model serial number on the engine housing or crankcase.

ComponentIdentification
ModelFS 90
Engine Type2-stroke, single-cylinder, air-cooled
Displacement27.2 cm³ (1.66 cu. in.)
Powerhead Serial NumberLocated on engine housing (e.g., 123456789)
Ignition SystemElectronic, capacitor discharge (CDI)
Fuel/Oil Mix50:1 (STIHL HP Ultra oil recommended)
Shaft TypeSolid, straight drive shaft
Standard Cutting AttachmentSTIHL AutoCut C 5-2 line head or circular saw blade

Engine Assembly Parts

Crankcase, cylinder, piston, crankshaft, and related components.

  1. Cylinder: Part # 1128 020 1201 – Includes cylinder, fins, and transfer ports.
  2. Piston: Part # 1128 030 2001 – Piston with rings and wrist pin.
  3. Crankshaft: Part # 1128 040 0600 – Complete crankshaft assembly.
  4. Crankcase: Part # 1128 050 0601 – Two-piece crankcase halves.
  5. Bearings & Seals: Main bearings, crankshaft seals, and gaskets.

WARNING! Engine disassembly requires special tools and expertise. Always disconnect the spark plug boot before servicing.

Drive Shaft & Gearbox Parts

Components transmitting power from the engine to the cutting head.

  1. Drive Shaft: Part # 1128 291 0600 – Solid steel shaft within the trimmer tube.
  2. Flexible Coupling: Part # 1128 292 0600 – Connects engine output to drive shaft.
  3. Gearbox (Cutting Head End): Part # 1128 300 0601 – Bevel gear assembly.
  4. Gearbox Seals & Bearings: Part # 1128 301 0600 – Seal and bearing kit.
  5. Trimmer Tube: Part # 1128 280 0600 – Main shaft housing.

CAUTION! Inspect the drive shaft for bends or damage. A damaged shaft can cause vibration and gearbox failure.

Cutting Attachment Parts

Handle & Control Parts

Handle assembly, throttle trigger, lockout, and control cables.

Loop Handle: Part # 1128 790 0600 – Main handle with vibration damping. Throttle Trigger: Part # 1128 817 0600 – Complete trigger assembly with switch. Throttle Cable: Part # 1128 818 0600 – Cable connecting trigger to carburetor. Handlebar Mount: Part # 1128 791 0600 – Clamp assembly for attaching handle. Master Control Lever: Part # 1128 830 0600 – Combination stop switch / choke / run control.

Fuel System Parts

Fuel tank, carburetor, fuel lines, and filter.

  1. Fuel Tank: Part # 1128 350 0601 – Polyethylene tank with integrated cap.
  2. Carburetor: Part # 1128 120 0602 – Zama C1Q-S series carburetor assembly.
  3. Fuel Filter: Part # 1128 358 0600 – In-tank fuel filter.
  4. Fuel Line: Part # 1128 359 0600 – Tygon fuel line (bulk per meter).
  5. Impulse Line: Part # 1128 357 0600 – Line connecting crankcase to carburetor.

Tip: Always use fresh fuel mix and replace the fuel filter annually or if engine runs poorly.

Air Filter & Exhaust System

Components for air intake and exhaust gas management.

  1. Air Filter: Part # 1128 140 0600 – Foam filter element.
  2. Air Filter Cover: Part # 1128 141 0600 – Plastic cover with latch.
  3. Muffler: Part # 1128 150 0601 – Complete muffler with spark arrestor screen.
  4. Spark Arrestor: Part # 1128 152 0600 – Replaceable screen insert.
  5. Exhaust Gasket: Part # 1128 151 0600 – Cylinder-to-muffler gasket.

WARNING! Regularly clean the air filter and spark arrestor screen. A clogged screen can cause overheating.

Ignition System Parts

Spark plug, ignition module, and wiring.

PartPart NumberDescription
Spark Plug1128 170 0601Bosch WSR 6 F or equivalent
Ignition Module (CDI)1128 400 0601Electronic control unit
Stop Switch Wire1128 402 0600Wire from switch to CDI
Spark Plug Boot1128 171 0600High-tension lead terminal

Starter Assembly Parts

Recoil starter pulley, rope, spring, and housing.

Starter Assembly Complete: Part # 1128 190 0601 – Includes pulley, spring, rope, and handle. Starter Rope: Part # 1128 193 0600 – Replacement rope. Starter Spring: Part # 1128 192 0600 – Recoil spring. Starter Handle: Part # 1128 194 0600 – Plastic grip.

Fasteners & Miscellaneous Parts

Screws, nuts, washers, antivibration elements, and decals.

Parts Ordering & Diagrams

Use exploded-view diagrams with reference numbers to identify parts.

Symptom / NeedReference SourceAction
Identify a specific partExploded View Diagram (Fig. 1-10)Match the number in the diagram to the parts list.
Order genuine STIHL partsPart Number from this manualProvide part number to an authorized STIHL dealer.
Verify part compatibilityModel & Serial NumberConfirm your FS 90 serial number with the dealer.
Assembly guidanceSTIHL Repair ManualRefer to the separate service repair manual for procedures.
Parts not listedAuthorized DealerContact a STIHL dealer with your serial number for assistance.

Note: Part numbers are subject to change. Always confirm with your dealer using your unit's serial number.

STIHL Support: For technical or parts assistance, contact an authorized STIHL servicing dealer or visit www.stihlusa.com.

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