How To Start A STIHL MS 170 Chainsaw: The Complete Technical Starting And Troubleshooting Guide

To start a STIHL MS 170 chainsaw, engage the chain brake, depress the throttle trigger lockout and trigger simultaneously, and push the Master Control Lever all the way down to the Full Choke position. Pull the starter rope firmly until the engine briefly fires (typically 2 to 5 pulls), then immediately move the Master Control Lever up one position to the Half-Throttle/Warm Start setting. Pull the starter rope again to start the engine, and immediately blip the throttle trigger to transition the lever to the normal Run position, ensuring the chain brake is disengaged before cutting.

Pre-Operation Inspection and Safety Protocol

Prior to starting the STIHL MS 170, a systematic pre-flight inspection is necessary to protect the operator and prevent catastrophic damage to the engine, guide bar, and cutting chain. The MS 170 is a high-revving, lightweight 30.1cc two-stroke engine spinning a sharp cutting chain at speeds exceeding 50 miles per hour. Neglecting basic checks can lead to cylinder scoring, premature clutch wear, or severe kickback injuries.

Essential Pre-Start Checklist

• Engine Fuel Mixture: Fresh, unleaded gasoline with a minimum octane rating of 89 mixed at a precise 50:1 ratio with high-quality air-cooled two-stroke engine oil (such as STIHL HP Ultra). Do not use fuel containing more than 10% ethanol (E10), as it causes phase separation, running hot, and deteriorated fuel lines.
• Bar and Chain Lubrication: Fill the bar oil reservoir with dedicated, high-tack bar and chain lubricant. Never run the saw without bar oil; it prevents friction, overheating, and metal-to-metal binding.
• Chain Tension Calibration: The cutting chain must be properly tensioned. When cold, the drive links must not sag out of the bottom of the guide bar groove, yet you should be able to pull the chain freely along the bar by hand (always wear heavy leather gloves during this check).
• Safety Gear (PPE): Safety glasses or face shield, hearing protection (earmuffs with a minimum NRR rating of 22 dB), steel-toe work boots, and heavy-duty chainsaw chaps constructed with cut-retardant ballistic fibers.
• Mechanical Integrity: Inspect the spark plug boot for secure attachment, verify the chain catcher peg on the bottom of the saw is intact, and ensure the muffler screen is clear of carbon buildup.

Operating Metrics and Constraints

• Estimated Prep Time: 5 to 10 minutes.
• Required Tools: STIHL Combination wrench (scrench), protective gloves, fuel mixing container.
• Financial Investment: Standard maintenance costs (fuel stabilizer, 2-stroke oil, bar lubricant) generally run between $15 and $30 per season.

Step-by-Step STIHL MS 170 Cold Start Procedure

Starting a cold engine requires an enriched fuel-to-air ratio. The STIHL MS 170 utilizes a single Master Control Lever to actuate the choke, throttle lock, and ignition switch simultaneously. Understanding the internal physics of this mechanism prevents common starting errors like engine flooding.

Step 1: Engage the Chain Brake

Push the hand guard forward toward the guide bar. You will hear an audible click as the internal brake band wraps tightly around the clutch drum, locking the sprocket. This safety step prevents the cutting chain from spinning when the engine fires up at high idle speed.

Warning: Never attempt to start the chainsaw with the chain brake disengaged. When the engine starts on half-throttle, the clutch engages immediately, and a spinning chain can cause severe lacerations if it contacts the ground or your body.

Step 2: Set the Master Control Lever to Full Choke

To place the Master Control Lever into the lowest position (Full Choke), you must bypass an internal physical lock.

1. Grip the rear handle of the chainsaw.
2. Press down on the throttle trigger lockout lever on top of the handle with your palm.
3. Squeeze the throttle trigger underneath the handle with your index finger.
4. With your left thumb, push the Master Control Lever all the way down to the bottom position (indicated by the closed choke symbol).
5. Release the throttle trigger and lockout lever, then release the Master Control Lever. It will remain locked in the Full Choke position.

Step 3: Secure the Chainsaw on Flat Ground

Do not "drop start" the chainsaw. Drop starting is an incredibly dangerous practice that leaves you with zero control over the bar tip, risking catastrophic kickback.

1. Place the chainsaw flat on clear, level ground. Ensure the cutting chain and guide bar are not contacting any twigs, rocks, or debris.
2. Slip the toe of your right work boot completely inside the rear handle loop to pin the back of the saw to the ground.
3. Firmly grasp the front handlebar with your left hand, locking your elbow straight. This creates a rigid tripod base of control between your foot, your left hand, and the ground.

Step 4: Pull the Starter Rope to Achieve "First Ignition"

With your right hand, grip the starter rope handle.

1. Pull the starter rope slowly outward until you feel positive resistance (the starter pawls engaging the flywheel).
2. From this point, pull the rope upward with a rapid, powerful, vertical stroke.
3. Guide the rope back into the housing slowly; do not let it snap back violently, as this damages the recoil spring and starter rope guide.
4. Repeat this motion until the engine briefly fires, making a distinct, muffled "cough" or "burp" sound, and then immediately dies. This typically occurs within 2 to 5 pulls.

Pro-Tip: Do not pull the rope more than 5 times on Full Choke. If you continue to pull the rope after the engine "coughs" without moving the lever, raw fuel will flood the combustion chamber, soaking the spark plug and preventing the engine from firing.

Step 5: Transition to the Half-Throttle/Warm Start Position

Once the engine has sputtered, you must open the choke butterfly valve while keeping the engine at high idle to allow air to mix with the fuel.

1. Without touching the throttle trigger (touching the trigger will release the starting lock), push the Master Control Lever up one position to the half-throttle setting (indicated by the warm start/half-throttle symbol).
2. Keep your right foot in the rear handle and your left hand on the front handlebar.
3. Pull the starter rope with the same rapid, firm motion. The engine should fire up and continue running within 1 to 3 pulls.

Step 6: Disengage High Idle and Return to Run

When the engine starts in the half-throttle position, it will run at a high, loud RPM, and the clutch will try to spin the chain (though blocked by the activated chain brake).

1. Immediately tap or "blip" the throttle trigger with your right finger.
2. Squeezing the trigger automatically releases the internal catch, causing the Master Control Lever to spring upward to the normal running position (indicated by the "I" symbol). The engine will drop down to a smooth, low idle.
3. Lift the chainsaw by the handlebar, pull the front hand guard back toward the front handle until it clicks, and begin cutting. The chain will only spin when you squeeze the throttle trigger.

Executing a Warm Start (Hot Restart)

If you have recently run the chainsaw and the engine is still warm, the fuel within the carburetor has already vaporized, and the combustion chamber is primed. Starting a warm engine with the choke on will instantly flood the motor.

Step 1: Engage the Chain Brake

Push the front hand guard forward to lock the chain.

Step 2: Set the Master Control Lever to the Warm Start Position

Squeeze the throttle lockout and trigger, and push the Master Control Lever down. Slide it up to the half-throttle position. If the engine has only been off for a minute or two, you can often leave the Master Control Lever in the normal "I" Run position and proceed.

Step 3: Pull the Starter Rope

With the saw secured on the ground, pull the starter rope. The engine should catch and run on the first or second pull. If it fires in half-throttle, instantly blip the trigger to return the Master Control Lever to the "I" Run position to drop the engine to idle.

STIHL MS 170 Technical and Calibration Specifications

The following table provides the precise factory settings, fluid requirements, and clearance tolerances necessary to keep your STIHL MS 170 running optimally.

Troubleshooting Common MS 170 Starting Failures

Chainsaws operate in high-dust, high-vibration environments, making them prone to starting hiccups. Below are the three most common starting failures, their technical causes, and how to resolve them on the job site.

Scenario 1: The Engine is Flooded (Smells of gas, won't fire on warm start)

• Root Cause: The starter rope was pulled too many times on Full Choke, or the warm start was attempted with the choke engaged. Excess raw fuel has saturated the spark plug, filling the combustion chamber and preventing the spark from jumping the plug gap.
• Actionable Fix:
  
  
  1. Turn off the machine by moving the Master Control Lever to the Stop "0" position.
  2. Use your scrench to remove the top engine shroud and unscrew the spark plug.
  3. If the spark plug electrode is wet with fuel, wipe it clean with a dry cloth and blow air into the cylinder plug hole to dry it out.
  4. Hold the chainsaw upside down with the spark plug removed and pull the starter rope 5 to 10 times to expel excess fuel from the combustion chamber.
  5. Clean the spark plug electrode with a wire brush, check the gap (0.020 in), and reinstall it.
  6. Reattach the spark plug boot and shroud. Set the Master Control Lever directly to the "I" Run position (no choke) and pull the starter rope firmly until it starts.

Scenario 2: The Starter Rope is Hard to Pull or Seized

• Root Cause: This can be caused by hydraulic lock (the cylinder is completely filled with liquid fuel), a broken recoil spring, or a seized engine due to using straight gasoline without two-stroke oil.
• Actionable Fix:
  
  
  1. Remove the spark plug and attempt to pull the starter rope.
  2. If the rope pulls freely with the plug removed, the issue was hydraulic lock; dry the plug and cylinder as detailed in Scenario 1.
  3. If the rope remains stuck or hard to pull, remove the four screws holding the starter housing to the side of the saw. Check for wood chips jammed in the flywheel fins or a tangled recoil pulley.
  4. If the flywheel cannot be rotated manually by hand with the spark plug removed, the piston has likely seized inside the cylinder due to lack of lubrication. The engine will require a rebuild.

Scenario 3: Engine Starts, Bogs Down, and Dies When Throttle Squeezed

• Root Cause: A clogged fuel filter inside the gas tank, a dirty spark arrestor screen in the muffler, or a carburetor that needs adjustment due to temperature or elevation changes.
• Actionable Fix:
  
  
  1. Pull the fuel filter out of the gas tank using a bent wire hook; if it is dark, gummy, or clogged, replace it with a new filter.
  2. Unscrew the small metal screen located on the exhaust outlet of the muffler. If it is black and blocked with carbon, clean it with a wire brush or burn the carbon off with a propane torch, then reinstall it.
  3. Locate the "LA" idle speed adjustment screw on the right side of the carburetor. If the engine dies at idle, turn the screw clockwise until the engine idle stabilizes.

Frequently Asked Questions

Why does my STIHL MS 170 die as soon as I take the choke off?

This usually happens because the engine is still cold and has not had enough fuel vaporized in the crankcase to run on a normal mixture. Always let the chainsaw idle in the half-throttle position for 5 to 10 seconds before blipping the trigger to return it to the normal "I" Run position. If it continues to die, check for a vacuum leak in the fuel line or a dirty carburetor jets.

What is the difference between cold start and warm start positions?

The cold start (Full Choke) position closes a physical butterfly valve inside the carburetor throat, blocking air and drawing in a heavy concentration of fuel to prime a cold cylinder. The warm start (Half-Throttle) position leaves the choke valve open to allow maximum airflow but mechanically locks the throttle open slightly, keeping the engine at a higher idle speed to ensure it catches easily when already warm.

Can I use regular gasoline without oil in my STIHL MS 170?

No. Never use straight gasoline in a two-stroke engine. Two-stroke engines do not have an internal oil reservoir; they rely entirely on the oil mixed into the gasoline to lubricate the crankshaft bearings, piston pin, and cylinder walls. Running a STIHL MS 170 on straight gasoline will destroy the engine in less than a minute of operation.

Why does the cutting chain spin while the chainsaw is idling?

If the chain is spinning while the engine is at idle and the chain brake is off, either your idle speed (LA screw) is set too high, or you have a broken clutch spring. Turn the "LA" screw counter-clockwise to lower the idle RPM. If the chain continues to spin at low speeds, the clutch springs have lost tension or broken, requiring a clutch assembly replacement.

Precision Performance Maintenance

Keep your STIHL MS 170 operating like new by using premium fuels, performing routine spark plug inspections, and sharpening your cutting chain regularly. Investing a small amount of time in preventative maintenance ensures your chainsaw starts reliably on the very first pull every single season.