Stihl Carburetor Repair Manual

This manual provides comprehensive instructions for the repair, maintenance, and troubleshooting of Stihl chainsaw and power equipment carburetors. It covers common models including the Zama, Walbro, and Tillotson carburetors used across Stihl's product line. Below are key sections covering safety, identification, disassembly, cleaning, adjustment, reassembly, and common issues.

1. Safety Precautions 2. Carburetor Identification 3. Tools & Materials Required 4. Disassembly Procedure 5. Cleaning & Inspection 6. Diaphragm & Gasket Replacement 7. Needle Valve & Jet Cleaning 8. Reassembly Instructions 9. Adjustment & Tuning 10. Troubleshooting Common Problems 11. Specifications & Parts List

Safety Precautions

Before beginning any repair, ensure your safety and the integrity of the equipment.

Precaution	Description
Work Area	Work in a clean, well-ventilated area away from sparks or open flames.
Fuel Handling	Drain all fuel from the tank and carburetor. Fuel is highly flammable.
Personal Protective Equipment (PPE)	Wear safety glasses and nitrile gloves to protect from chemicals and small parts.
Tool Safety	Use the correct tools. Keep fingers clear of springs and small, sharp components.
Component Handling	Organize parts in order of removal. Avoid losing small screws, springs, and check valves.

WARNING! Failure to follow safety procedures can result in fire, injury, or damage to the carburetor.

Carburetor Identification

Identify your carburetor model before ordering parts. The model number is typically stamped on the carburetor body or lever plate.

Locate the identification tag or stamped numbers on the carburetor body.
Common Stihl series: C1Q, C3M, C1U, WT, etc.
Match the model to the correct repair kit (diaphragms, gaskets, needle valve).

Tip: Take a clear photo of the carburetor and any numbers before disassembly.

Tools & Materials Required

Basic Tools: Screwdrivers (flathead, Phillips #1, #2), needle-nose pliers, small socket set.
Cleaning Supplies: Carburetor cleaner spray, compressed air, ultrasonic cleaner (optional), lint-free cloths.
Replacement Parts: Carburetor rebuild kit (model-specific), fuel line, fuel filter.
Safety: Safety glasses, gloves, container for small parts.
Tuning Tools: Tachometer for final adjustment.

Disassembly Procedure

Systematic disassembly is crucial for successful repair.

Remove the carburetor from the engine: Disconnect fuel lines, throttle linkage, and mounting nuts.
External components: Remove air filter cover, choke lever, and throttle plate screws as needed.
Main body: Remove the four or six screws securing the two halves of the carburetor.
Internal parts: Carefully lift off the cover, exposing diaphragms, gaskets, and the metering lever.
Note the orientation and position of all springs, check valves, and the inlet needle.

CAUTION! Do not force components. If stuck, apply a small amount of penetrating oil.

Cleaning & Inspection

Thorough cleaning is the most important step in carburetor repair.

Process: 1. Soak all metal parts in carburetor cleaner. 2. Use compressed air to blow out all passages, including the main jet, idle jet, and impulse channel. 3. Inspect the carburetor body for cracks, warping, or damaged threads. 4. Check the throttle and choke shafts for excessive wear or play.

Key Areas: High-speed (H) and Low-speed (L) adjustment screw ports, fuel inlet screen, venturi.

Diaphragm & Gasket Replacement

Diaphragms and gaskets are wear items and should be replaced during every rebuild.

Remove the old diaphragm and gasket from the fuel pump and metering chambers.
Clean the sealing surfaces completely of any old adhesive or residue.
Install the new diaphragm from the repair kit, ensuring it is not pinched or folded.
Set the metering lever height. The lever should be flush with the carburetor body surface (use the gauge provided in the kit).
Replace the cover gasket and ensure the diaphragm is properly aligned with the impulse hole.

WARNING! An incorrectly set metering lever will cause flooding or lean running.

Needle Valve & Jet Cleaning

The inlet needle valve and jets control fuel flow and are common failure points.

Inlet Needle: Remove the seat and inspect the needle tip and spring for wear. Replace if the tip is grooved or not sealing. Jets: Remove the H and L jets with the correct screwdriver. Soak and blow through with compressed air. Ensure the tiny orifices are completely clear. Welch Plug: Some models have a pressed-in plug covering internal channels. Do not remove unless necessary for cleaning; replace if removed.

Reassembly Instructions

Reassemble in the reverse order of disassembly.

Install the cleaned jets and needle valve assembly.
Place the new pump and metering diaphragms and gaskets in their chambers.
Carefully mate the two halves of the carburetor, ensuring diaphragms are positioned correctly.
Install and tighten screws in a criss-cross pattern to avoid warping.
Reinstall external components: throttle plate, choke lever, and linkages.

Tip: Do not overtighten screws. Snug is sufficient to prevent air leaks.

Adjustment & Tuning

Initial settings before starting the engine.

Screw	Initial Setting	Function
High-Speed (H)	1 turn out from lightly seated	Controls fuel at full throttle
Low-Speed (L)	1 turn out from lightly seated	Controls fuel at idle and low throttle
Idle Speed (LA or T)	Set so chain just stops moving	Sets idle RPM

Fine Tuning: 1. Start engine and warm up for 5 minutes. 2. Adjust idle speed screw so engine runs smoothly and chain does not move. 3. Turn L screw for fastest, smoothest idle, then return to set idle speed. 4. With engine at full throttle (no load), adjust H screw for peak RPM, then richen slightly (1/8 turn) for safety.

Troubleshooting Common Problems

Symptom	Possible Cause	Corrective Action
Engine won't start	Flooded, no fuel, bad diaphragm	Check spark plug for wetness; verify fuel flow; replace pump diaphragm.
Engine runs lean (high RPM, overheating)	Air leak, clogged jet, bad gasket	Spray carb cleaner around seals to find leak; clean H jet; replace gaskets.
Engine runs rich (smoky, bogging)	Dirty air filter, stuck needle, high metering lever	Clean/replace air filter; clean/inspect inlet needle; reset metering lever height.
Poor idle or stalling	Clogged L jet, idle screw setting, air leak	Clean L jet and passage; adjust L and idle screws; check for crankcase seals.
Fuel leaking from carburetor	Stuck inlet needle, damaged diaphragm, cracked body	Clean/replace needle and seat; replace diaphragm; inspect body for cracks.

Specifications & Parts List

Common Repair Kits: RK-23, RK-88, RK-101 (Refer to your specific model).
Diaphragm Material: Nitrile rubber (fuel resistant).
Jet Sizes: Vary by model and engine size (e.g., .026", .030").
Torque Values:Carburetor mounting nuts: 8-10 ft-lbs. Body screws: 6-8 in-lbs (finger tight plus 1/4 turn).

Warranty Note: Using non-genuine Stihl parts may affect performance and warranty.