Master The Cold And Warm Start: How To Start A STIHL Chainsaw MS 170 Safely

To start a STIHL MS 170 chainsaw, engage the chain brake, squeeze the throttle trigger to set the Master Control Lever to full choke, and pull the starter rope until the engine briefly fires. Immediately move the lever up one click to the half-choke position, pull the rope to start the engine, and then tap the throttle to transition to the run position. This standard starting sequence prevents engine flooding and ensures a safe, reliable ignition within three to five pulls.

The STIHL MS 170 is a highly popular, lightweight chainsaw prized for its reliability in firewood cutting, property maintenance, and light felling. However, mastering its specific starting procedure—particularly understanding its unique multi-position Master Control Lever—is essential to prevent engine flooding, minimize physical wear on the recoil starter, and ensure operator safety. Because the MS 170 does not feature a manual fuel primer bulb or a decompression valve, relying on the correct mechanical starting sequence is paramount.

Pre-Operation & Equipment Checklist

Before attempting to start your STIHL MS 170, you must prepare the tool, inspect safety mechanisms, and wear the necessary protective gear. Operating a chainsaw without these precautions increases the risk of severe kickback injuries or permanent engine damage.

Essential Safety Gear (Personal Protective Equipment)

• Chainsaw Chaps or Pants: Must meet ASTM F1897 or ISO 11393 standards to protect your legs from accidental chain contact.
• Safety Glasses and Face Shield: High-impact eye protection meeting ANSI Z87.1 standards.
• Hearing Protection: Ear muffs or earplugs rated with a Noise Reduction Rating (NRR) of at least 25 dB.
• Heavy-Duty Work Gloves: Leather or cut-resistant gloves to protect your hands from sharp cutters and vibration.
• Protective Boots: Steel-toe or composite-toe boots with high-grip soles.

Required Fluids and Mechanical Checkpoints

• Fuel Mixture: Fresh, mid-grade (minimum 89 octane) unleaded gasoline mixed at a strict 50:1 ratio with high-quality 2-stroke air-cooled engine oil (preferably STIHL HP Ultra). Avoid fuels containing more than 10% ethanol (E10), as higher ethanol blends cause phase separation and damage carburetor diaphragms.
• Bar and Chain Lubricant: High-tack bar oil designed to resist slinging. The chain oil reservoir should be filled every time you refuel the chainsaw.
• Chain Tension: The chain should fit snugly against the underside of the guide bar but still turn easily by hand. When pulled upward from the top of the bar, the drive links should not fully exit the bar groove.
• Chain Brake Function: Ensure the front hand guard clicks cleanly forward into the engaged position and pulls back into the disengaged position.

Checklist Summary Table

Step-by-Step Ignition Process for the STIHL MS 170

Starting the STIHL MS 170 requires distinct procedures depending on whether the engine is cold (has not been run recently) or warm (has been run and shut down within the last 15 to 20 minutes).

Step 1: Engage the Chain Brake and Remove the Scabbard

Always start the chainsaw with the chain brake fully engaged. Push the black front hand guard forward toward the guide bar until you hear a sharp, audible click. This locks the clutch drum, preventing the saw chain from rotating along the bar when the engine ignites. Once the brake is engaged, slide the protective plastic scabbard off the guide bar to expose the cutting chain.

Warning: Never attempt to start the chainsaw without engaging the chain brake. If the engine starts at high idle with the brake disengaged, the chain will immediately spin, creating an extreme risk of contact injury.

Step 2: Squeeze and Lock the Master Control Lever

The STIHL MS 170 features a unified Master Control Lever on the rear handle that controls the choke, throttle lock, and ignition switch. To set the lever to the lowest position (Full Choke / Cold Start):

1. Press and hold down the throttle trigger lockout on top of the rear handle.
2. Squeeze the lower throttle trigger completely.
3. While holding both triggers, push the Master Control Lever all the way down past the detent point to the Full Choke position (represented by the closed choke flap symbol).

Pro-Tip: The Master Control Lever cannot be pushed down to the Full Choke position without first depressing the throttle trigger and lockout. Forcing the lever without squeezing the triggers will break the internal plastic linkages.

Step 3: Position and Secure the Chainsaw on the Ground

Place the chainsaw flat on firm, level ground. Ensure the cutting bar and chain are completely clear of the ground, branches, stones, or any other obstructions.

1. Place your right foot firmly inside the wide lower opening of the rear handle. This anchors the rear of the saw to the ground.
2. Grip the front handlebar firmly with your left hand, locking your elbow straight. This gives you complete leverage and prevents the bar from kicking upward during starting pulls.

Step 4: Pull the Starter Rope to Achieve the Engine "Burp"

With your left hand firmly gripping the front handlebar and your right foot securing the rear handle, grip the starter rope handle with your right hand.

1. Pull the starter rope slowly upward until you feel physical mechanical resistance (this engages the starter pawls with the flywheel).
2. Once resistance is felt, pull the starter rope upward with a rapid, vertical, and continuous stroke. Do not let the rope snap back; guide it gently back into the housing.
3. Repeat this motion until the engine fires briefly—often called a "burp" or "pop"—and then immediately dies. This typically occurs within 2 to 5 pulls.

Warning: Do not pull the starter rope more than 5 times while the Master Control Lever is in the Full Choke position. Continuous pulling on Full Choke after the initial ignition pop will flood the combustion chamber with fuel, wetting the spark plug and preventing the saw from starting.

Step 5: Switch to the Half-Choke (Warm Start) Position

Immediately after the engine makes its brief firing sound and dies, move the Master Control Lever up one position to the Half-Choke / Warm Start position (represented by the symbol with a diagonal line through the choke flap).

• Do not squeeze the throttle trigger while making this adjustment. Squeezing the trigger will automatically release the lever to the Run position, which you do not want yet.

Step 6: Pull the Starter Rope Until the Engine Ignites

Ensure the saw is still safely anchored with your foot and hand. Pull the starter rope with the same firm, rapid motion as before. Because the cylinder is now primed with fuel, the engine should start running within 1 to 3 pulls. It will run at a high, loud idle speed because the throttle lock is mechanically engaged in this position.

Step 7: Disengage the High Idle (The Throttle "Blip")

As soon as the engine starts and is running, briefly squeeze and release (blip) the throttle trigger. This action automatically releases the starting throttle lock, allowing the Master Control Lever to spring upward to the normal Run position (represented by the I symbol). The engine's speed will drop to a smooth, standard idle, and the chain will remain static as long as the chain brake is still engaged.

Step 8: Disengage the Chain Brake and Verify Lubrication

With the engine idling smoothly, lift the chainsaw by the handlebar and rear handle. Pull the front hand guard backward toward the front handlebar with your left hand until you hear a click. This disengages the chain brake, allowing the chain to spin freely.

• Before cutting, hold the chainsaw bar over a clean surface (like a tree stump or a piece of cardboard) and rev the engine slightly.
• A fine line of oil should fling off the tip of the bar onto the surface, indicating that the automatic oiler is functioning correctly.

STIHL MS 170 Engine Specifications and Starting Metrics

The following technical data details the operating parameters, fluid capacities, and electrical specifications that govern the starting and running performance of the STIHL MS 170.

Resolving Common MS 170 Starting Problems and Engine Flooding

If your STIHL MS 170 does not start after following the standard steps, it is highly likely that the engine has either flooded, has poor spark delivery, or is dealing with stale fuel issues. Use the following diagnostic pathways to resolve these common field issues.

Scenario 1: The Engine is Flooded (Smells strongly of gasoline, won't start after multiple pulls)

• Root Cause: The starter rope was pulled too many times while the Master Control Lever was in the Full Choke position, filling the combustion chamber with liquid fuel and soaking the spark plug.
• Actionable Fix:
  
  
  1. Flip the Master Control Lever to the Stop position (0).
  2. Use the combination wrench (scrench) to remove the top orange shroud cover and unscrew the spark plug.
  3. If the spark plug electrode is wet with fuel, wipe it dry with a clean cloth or blow it dry with compressed air.
  4. With the spark plug removed, tip the chainsaw upside down so the spark plug hole faces the ground. Pull the starter rope 10 to 15 times rapidly to clear excess liquid fuel from the crankcase.
  5. Reinstall the spark plug, torque it to specification (15-20 Nm), and reattach the ignition lead.
  6. Attempt to start the saw with the Master Control Lever set to the Run (I) or Half-Choke position without using the full choke again.

Scenario 2: The Starter Rope is Extremely Difficult to Pull

• Root Cause: Liquid fuel has filled the combustion chamber completely, causing a hydrostatic lock (liquid cannot be compressed), or there is physical damage within the recoil starter housing.
• Actionable Fix: Remove the spark plug and pull the starter rope. If the rope pulls freely, the issue is hydrostatic lock caused by severe flooding (follow the steps in Scenario 1). If the rope remains locked or hard to pull with the spark plug removed, unscrew the starter cover housing and check for a broken recoil spring, frayed starter cord, or melted plastic starter pawls.

Scenario 3: The Engine Starts but Dies Instantly When Accelerated

• Root Cause: The carburetor jets are partially clogged with varnish from old, ethanol-blended fuel, or the engine is drawing in too much air through a split fuel line or loose intake boot.
• Actionable Fix:
  
  
  1. Drain any fuel that has been sitting in the tank for more than 30 days.
  2. Refill the tank with fresh fuel mixed with a fuel stabilizer.
  3. Inspect the fuel filter located inside the fuel tank using a wire hook; if it is dark or clogged, pull it off and install a new OEM STIHL fuel filter.
  4. Check the spark arrestor screen inside the muffler exhaust port. If it is clogged with black carbon deposits, remove it and clean it with a wire brush or heat it with a torch to burn off the carbon.

Frequently Asked Questions

Why does my STIHL MS 170 not have a primer bulb?

The STIHL MS 170 is designed as an entry-level professional and homeowner saw, utilizing a highly simplified carburetor design. It relies entirely on the mechanical choke flap to restrict airflow, which increases vacuum within the carburetor throat to draw fuel directly into the combustion chamber during the initial starting pulls.

Can I start my MS 170 while dropping it in the air (drop-starting)?

No, drop-starting is an incredibly dangerous practice that is strictly prohibited by STIHL and safety organizations worldwide. Drop-starting involves throwing the saw downward with one hand while pulling the starter rope with the other, which causes you to lose physical control of the guide bar and can result in severe kickback injuries.

How do I start the MS 170 if it is already warm?

To start a warm engine, do not use the Full Choke position. Simply set the Master Control Lever to the Run (I) position, ensure the chain brake is engaged, place the saw on the ground, and pull the starter rope. If it does not catch on the first two pulls, move the lever down to the Half-Choke ()I() position to provide a slightly richer mixture and high idle, then pull again.

What should I do if my chainsaw chain spins while the engine is idling?

If the chain spins while the engine is at idle and the chain brake is disengaged, your idle speed is set too high, or your clutch springs are broken. Use a small carburetor adjustment screwdriver to turn the idle speed screw (marked LA on the side of the housing) counterclockwise until the chain stops spinning. If adjusting the LA screw does not stop the chain, have a dealer inspect the clutch assembly.

Maintain Your STIHL MS 170 for Peak Performance

Keeping your chainsaw in optimal running condition requires regular maintenance of its fuel, filtration, and ignition systems. For replacement parts, high-quality lubricants, or professional servicing, always consult an authorized local STIHL dealer to keep your equipment running safely and efficiently.