How To Start A STIHL MS 170 Chainsaw: The Ultimate Cold & Warm Start Guide

Starting a STIHL MS 170 chainsaw correctly requires mastering the 4-position Master Control Lever to prevent engine flooding and ensure immediate ignition. By setting the chain brake, engaging full choke until the initial combustion "pop," and immediately shifting to half-choke, operators achieve reliable starting within three to five pulls. Adhering to proper ground-starting posture and maintaining a precise 50:1 fuel mixture guarantees peak 30.1 cc engine performance and long-term operational reliability.

Pre-Operation Safety Standards & Equipment Checklist for the STIHL MS 170

Before attempting to start the STIHL MS 170, operators must conduct a systematic safety audit and verify fuel quality. The MS 170 features a 30.1 cc STIHL 2-MIX engine that depends on exact fuel ratios and unrestricted air movement to generate its rated 1.3 kW (1.7 bhp) output. Skipping basic pre-start checks can result in severe personal injury, premature engine seizure, or rapid clutch wear.

Essential Gear, Tools, and Operational Requirements

• Personal Protective Equipment (PPE): Chainsaw chaps complying with ASTM F1897, non-slip steel-toe safety boots, heavy-duty leather gloves, protective eyewear certified to ANSI Z87.1, and hearing protection with a minimum Noise Reduction Rating (NRR) of 25 dB.
• Fuel & Lubricants: Fresh 89-octane mid-grade unleaded gasoline blended with premium two-stroke engine oil at an exact 50:1 ratio (2.6 fl. oz. oil per 1 gallon of gas). Ethanol content must remain below 10% (E10 maximum) to prevent carburation diaphragm degradation. Bar and chain lubricant must be filled to capacity in the designated reservoir.
• Mechanical Verification: Proper chain tension check (the chain should fit snug against the underside of the guide bar guide rails but still rotate freely by hand when the chain brake is disengaged).
• Duration & Labor Benchmark: Pre-start inspection requires 2–3 minutes; cold-starting execution takes under 60 seconds when following correct choke sequencing.

Step-by-Step Starting Procedure for the STIHL MS 170

Step 1: Engage Safety Controls and Assume Safe Ground-Starting Posture

Place the STIHL MS 170 on flat, clean ground devoid of loose gravel, twigs, or debris that could be drawn into the flywheel cover or contact the saw chain. Verify that the guide bar and chain are suspended off the ground and completely clear of all obstructions.

1. Push the front hand guard forward away from the handlebar until it clicks firmly into place to engage the chain brake. This mechanically locks the clutch drum, preventing chain rotation upon startup.
2. Remove the plastic guide bar scabbard.
3. Assume the standardized ground-starting position: Place your right boot toe securely inside the rear handle loop. Place your left hand firmly on the front handlebar, locking your elbow straight to maintain absolute physical control over the powerhead.

Warning: Never "drop-start" a chainsaw by pulling the starter rope with one hand while dropping the powerhead with the other. This unstable method causes severe loss of physical control, exposing the operator to kickback and severe laceration hazards.

Step 2: Set the Master Control Lever to Cold Start (Full Choke)

The STIHL MS 170 uses a single unified Master Control Lever (Combipro switch) controlling the ignition circuit, throttle latch, and choke butterfly valve. Moving this lever into the lowest position requires a specific sequence.

1. Depress the throttle trigger interlock (top safety lever on the rear handle) and squeeze the bottom throttle trigger simultaneously.
2. While holding both triggers completely depressed, slide the Master Control Lever all the way down to Position 4 (Full Choke / Cold Start symbol marked with a closed choke gate).
3. Release the throttle trigger and interlock lever. The Master Control Lever will remain locked in Position 4, holding the throttle valve slightly open in a fast-idle position while keeping the choke valve fully closed.

Pro-Tip: If the Master Control Lever refuses to slide into Position 4, you are not depressing the throttle trigger fully. Do not force the lever, as this can bend the inner mechanical linkages.

Step 3: Execute Initial Pulls Until Primary Ignition ("The Pop")

With the saw stabilized and the choke set to Position 4, you must pull the starter cord until the engine briefly fires. This short combustion cycle is commonly known as "the pop" or "false start."

1. Grip the starter grip handle with your right hand. Pull the rope out slowly until you feel distinct mechanical resistance (top dead center of the piston stroke).
2. Once resistance is felt, pull the starter rope briskly upward in a vertical motion. Do not pull the rope to its absolute maximum length (approximately 30 inches) to prevent snapping the recoil spring or rope anchor.
3. Guide the starter rope back into the housing smoothly—do not let it snap back freely against the crankcase.
4. Repeat this firm pulling motion. Usually between 2 to 4 pulls, the engine will briefly ignite, produce a short "burble" or "pop" sound, and immediately stall out.

Warning: Stop pulling immediately after you hear the engine pop! Pulling the starter cord more than once or twice after the initial pop while remaining in Position 4 (Full Choke) will flood the combustion chamber with liquid fuel, drenching the spark plug and preventing ignition.

Step 4: Transition to Half-Choke (Warm Start) and Fire the Engine

Once the engine delivers its initial ignition pop, the engine cylinder is primed with a concentrated air-fuel mix. You must now open the choke valve slightly to allow adequate airflow into the carburetor venturi.

1. Push the Master Control Lever up one single notch into Position 3 (Half-Choke / Warm Start / Start position). Do not touch the throttle trigger while doing this, or the lever will jump directly to Position I (Run).
2. Pull the starter rope briskly using the exact same motion as Step 3.
3. Within 1 to 3 pulls, the engine will start and run at a high idle speed (fast idle).

Step 5: Disengage Fast Idle and Release the Chain Brake

Because the engine is currently running at fast-idle speed with the throttle latch engaged, the centrifugal clutch is attempting to turn the drive sprocket against the engaged chain brake. You must clear the fast idle immediately to prevent clutch shoes and drum overheating.

1. Immediately blip (press and quickly release) the throttle trigger. The Master Control Lever will automatically spring up into Position I (Normal Run position), returning the carburetor to standard engine idle speed (approx. 2,800 RPM).
2. Allow the engine to idle smoothly for 15–30 seconds to warm up the cylinder walls and establish consistent crankcase pressure.
3. Pull the front hand guard back toward the handlebar until a sharp click is heard, releasing the chain brake.
4. Verify that the saw chain remains motionless at idle. Squeeze the throttle trigger to begin cutting operations.

Step 6: Executing a Warm Engine Restart Procedure

If the chainsaw has already been running, is at operating temperature, or has been shut off for less than 15–20 minutes, skip the full choke position entirely to avoid flooding.

1. Engage the chain brake by pushing the front hand guard forward.
2. Depress the throttle trigger lockout and main trigger together.
3. Move the Master Control Lever down to Position 3 (Half-Choke / Warm Start).
4. Place the saw in a stable ground position or lock the rear handle securely between your knees/thighs.
5. Pull the starter rope briskly. The engine will start within 1–2 pulls.
6. Blip the throttle trigger to reset the Master Control Lever to Position I (Run), then pull back the front hand guard to disengage the chain brake.

STIHL MS 170 Technical Specifications & Master Control Matrix

Understanding the exact technical metrics, clear tolerances, and lever positions of the STIHL MS 170 ensures correct operational mechanics during daily maintenance and starting operations.

Troubleshooting Common MS 170 Starting Failures

| Column 1 | | :--- | | [Engine Won't Start] | | | | | [Engine Flooded?] [No Ignition Pop?] | | - Smells raw gas - Fuel old (>30 days) - Pull cord wet - Spark plug fouled - Cord hard to pull - Stop switch grounded | | v v [Clear Flooded Engine] [Inspect & Service] 1. Set Lever to Position I 1. Replace with 50:1 fresh fuel 2. Pull plug, dry electrode 2. Check plug gap (0.020") 3. Invert saw, pull cord 10x 3. Verify spark against cylinder 4. Reinstall plug, start in Pos 3 4. Clean air filter & spark arrestor

Scenario 1: Flooded Engine from Over-Choking

• Root Cause: The operator pulled the starter rope too many times in Position 4 (Full Choke) after the primary ignition pop occurred. Liquid fuel has saturated the crankcase and wet the spark plug electrode, preventing spark jump.
• Actionable Fix:
  
  
  1. Move the Master Control Lever up to Position 0 (Stop).
  2. Remove the top engine shroud using a STIHL combination wrench (19 mm socket).
  3. Disconnect the spark plug boot and remove the spark plug using the 19 mm socket end.
  4. Inspect the plug: If the electrode is soaked with fuel, wipe it clean and dry, or clean it thoroughly with electrical contact cleaner and a wire brush.
  5. Turn the chainsaw upside down so the spark plug hole points toward the ground.
  6. Pull the starter cord 10 to 15 times rapidly while upside down to expel excess unburned fuel from the combustion chamber.
  7. Reinstall the dry spark plug, torque it to 20 Nm (14.7 ft-lbs), reattach the boot, and replace the shroud.
  8. Set the Master Control Lever directly to Position 3 (Half-Choke / Warm Start)—do not go to full choke. Pull the cord until the engine starts.

Scenario 2: Engine Starts But Stalls Immediately Upon Acceleration

• Root Cause: The engine has not reached minimal thermal operating temperature, or the idle adjustment screw (LD screw) is set too lean, or stale ethanol-blended fuel has clogged the idle jet in the Zama carburetor.
• Actionable Fix:
  
  
  1. Restart the engine in Position 3 and allow it to idle in Position I for a full 45 to 60 seconds without pulling the throttle trigger.
  2. If stalling persists, drain the fuel tank completely and refill with fresh 50:1 premix fuel utilizing non-ethanol 91+ octane gasoline.
  3. Locate the carburetor adjustment access port on the right side of the shroud. Using a small flathead screwdriver, turn the Low-Speed setting screw (marked "LD") clockwise 1/8 to 1/4 turn to slightly increase low-end fuel delivery and idle speed.

Scenario 3: Starter Cord Has Extreme Mechanical Resistance or Lockup

• Root Cause: The combustion chamber is completely hydro-locked with liquid fuel, or hydro-lock has occurred alongside dynamic clutch assembly seizure or flywheel binding.
• Actionable Fix:
  
  
  1. Never force or yank the pull cord when extreme resistance is felt; doing so will strip the pawls on the starter cup or break the pull rope.
  2. Immediately remove the spark plug as outlined in Scenario 1.
  3. Pull the starter cord gently with the spark plug removed. If it pulls smoothly, hydro-lock was the culprit. Cycle the cord multiple times to clear liquid fuel before reinstalling the spark plug.
  4. If the cord remains locked with the spark plug out, remove the starter housing (4 T27 Torx screws) and inspect the recoil spring assembly and flywheel fan fins for mechanical obstruction or broken recoil pawls.

Scenario 4: Engine Refuses to Fire When Hot

• Root Cause: Vapor lock in the fuel line caused by excessive heat, or partial loss of compression due to thermal expansion on a worn piston ring, or ignition coil breakdown under high operating temperatures.
• Actionable Fix:
  
  
  1. Allow the saw to cool in a shaded area for 10 minutes.
  2. Set the Master Control Lever directly to Position I (Run) or Position 3 (Warm Start). Hold the throttle trigger wide open (squeeze fully) while placing your foot through the rear handle on the ground.
  3. Pull the starter cord 4 to 6 times with the throttle held wide open to flush vaporized gas bubbles through the carburetor.
  4. If the saw fails to start, pull the spark plug, re-attach the wire boot, ground the threaded outer metal shell of the plug against a clean metal cooling fin on the cylinder block, and pull the cord. Observe the gap: If no bright blue spark is visible across the 0.020 in gap, replace the ignition module coil.

Frequently Asked Questions

Why does my STIHL MS 170 flood so easily during a cold start?

The STIHL MS 170 relies on a compact Zama diaphragm carburetor that delivers a high fuel-to-air ratio when the Master Control Lever is set to Position 4 (Full Choke). Because the engine displacement is relatively small at 30.1 cc, the combustion chamber saturates rapidly. Pulling the starter cord more than once or twice after the engine gives its initial ignition "pop" draws raw liquid fuel directly into the cylinder, wetting the spark plug and stopping combustion.

How do I know if my MS 170 is in full choke or half choke?

The position of the choke is governed by the Master Control Lever located above the rear handle on the left side. The lowest position (Position 4, marked with a fully closed choke gate icon) is Full Choke. Moving the lever up one click detent to Position 3 places the saw in Half-Choke (Warm Start position). Position I is normal running mode, and the top position (Position 0) cuts the electrical ignition grounding circuit to stop the saw.

Can I start my MS 170 chainsaw without placing it on the ground?

Yes, experienced operators can utilize the "knee-lock" starting method as an alternative to ground starting. Place the rear handle firmly between your thighs, clamped tightly above the knees, while holding the front handlebar firmly with your left hand (elbow locked straight). Ensure the guide bar and chain project outward away from your body into clear air before pulling the starter cord with your right hand. Never drop-start a chainsaw under any circumstances.

What is the correct fuel mix for a STIHL MS 170?

The STIHL MS 170 requires a strict 50:1 fuel-to-oil ratio, achieved by mixing 2.6 fluid ounces of high-quality two-stroke engine oil per one gallon of unleaded gasoline. The gasoline must have a minimum anti-knock index of 89 octane and an ethanol content not exceeding 10% (E10). Using pre-mixed canned synthetic fuel (such as STIHL MotoMix) eliminates ethanol-related degradation and extends carburetor diaphragm life significantly.

Master Your STIHL Maintenance Routine

Mastering the starting workflow and proper choke mechanics of your STIHL MS 170 prevents unnecessary engine wear and eliminates starting frustration on the job site. Keep your saw performing at factory parameters by combining correct starting procedures with routine air filter cleanings, proper chain sharpening, and fresh, high-octane 50:1 fuel mix.