Stihl MS170 Won’t Start – Possible Causes and Their Solution

The STIHL MS 170 chainsaw is a reliable and versatile tool for various cutting tasks, whether it’s for professional use or tackling backyard projects. However, like any mechanical device, it can encounter issues that might prevent it from starting. Many people complain that my chainsaw won’t start and if you find yourself frustrated with the same non-starting MS 170, fear not.

In this comprehensive guide, we will delve into the potential causes behind this problem and provide you with step-by-step solutions to get your chainsaw up and running again.

Common Causes of Start-Up Issues

Before jumping into the solutions, let’s explore the common causes behind an STIHL MS 170 chainsaw failing to start:

  • Fuel Issues

One of the most frequent reasons for a chainsaw not starting is related to fuel problems. Old or stale fuel, incorrect fuel-to-oil mixture ratios, or contaminated fuel can all lead to difficulty in starting the engine.

  • Ignition Coil Problems

Faulty spark plugs, a damaged ignition coil, or disconnected wires can prevent the ignition system from generating a spark, hindering the starting process.

  • Airflow and Carburetor Problem

A clogged air filter or carburetor can disrupt the proper air-fuel mixture, leading to difficulties in starting the engine.

  • Flooded Engine

Repeatedly pulling the starter cord without the engine firing can flood the engine with excess fuel, making ignition difficult.

  • Compression Issues

Low compression due to worn-out piston rings or cylinder seals can reduce the engine’s ability to start.

  • Choke Misuse

Incorrect use of the choke, such as leaving it on after the engine warms up, can cause starting problems.

  • Vapor Lock Issue 

A vapor lock issue can occur when air or vapor blocks the normal flow of fuel in a chainsaw’s fuel system, preventing the engine from starting or running properly. While vapor lock is less common in modern chainsaws with proper fuel system designs, it can still occur under certain conditions. 

Solution Guide: Step by Step

Now that we’ve identified the potential causes, let’s go through the step-by-step troubleshooting process to analyze and resolve the problems with your STIHL MS 170 chainsaw:

Step 1: Check the Fuel System

  • Empty any old or stale fuel from the chainsaw’s tank.
  • Prepare a fresh fuel mixture following the manufacturer’s recommended fuel-to-oil ratio.
  • Clean or replace the fuel filter to ensure proper fuel flow.

Step 2: Inspect the Ignition Coil

  • Remove the spark plug and inspect its condition. Replace it if it’s damaged.
  • Check the spark plug gap; it should match the manufacturer’s specifications.
  • Examine the ignition coil for any signs of damage or loose connections.

Step 3: Clean the Air Filter and Carburetor

  • Remove the air filter cover and clean the air filter. Replace it if it’s damaged or excessively dirty.
  • Carefully clean the carburetor with a carburetor cleaner, ensuring all passages are clear.

Clean the Air Filter and Carburetor

Step 4: Check the Flooded Engine

  • Set the choke to the “Off” position.
  • Open the throttle fully.
  • Pull the starter cord several times to clear excess fuel from the engine.
  • Set the choke to the proper starting position and attempt to start the chainsaw again.

Step 5: Check Compression

  • Perform a compression test using a compression gauge to determine if the engine’s compression is within the recommended range.
  • If compression is low, consult a professional for further diagnosis and potential repairs.

Step 6: Properly Use the Choke

  • When starting a cold engine, engage the choke. Once the engine starts, gradually disengage the choke as it warms up.

Step 7: Vapor Lock issue

  • If you suspect a vapor lock, stop attempting to start the chainsaw and allow it to cool down. High engine temperatures can contribute to the vaporization of fuel in the fuel lines and carburetor.
  • Inspect the fuel lines for any kinks, sharp bends, or damage that could restrict the flow of fuel. Damaged or pinched fuel lines can contribute to vapor lock.
  • Ensure that the fuel tank cap and vent are functioning properly. 
  • If your chainsaw has a primer bulb, use it to draw fresh fuel into the carburetor. Priming can help to push out any air bubbles or vapor that might be causing the vapor lock.
  • If the chainsaw is hot, you can try cooling it down by placing it in a shaded area or using a fan to speed up the cooling process. This might help to dissipate any vapor that has built up.
  • If you’ve recently used the chainsaw, carefully loosen the fuel tank cap to release any pressure that might have built up. Be cautious, as fuel vapors might escape.

How to Start a Stihl MS 170 Chainsaw – Easy Steps

Starting a Stihl MS 170 chainsaw involves a specific sequence of actions to ensure proper and safe operation. Here’s a step-by-step guide on how to start the Stihl chainsaw:

Note: Always follow the manufacturer’s instructions and safety guidelines when operating any power equipment, including chainsaws.

  • Safety Gear: Put on the necessary safety gear, including eye protection, hearing protection, gloves, and appropriate clothing.
  • Chain Brake: Activate the chain brake by pushing the front-hand guard forward. This is the bar in front of the top handle.
  • On/Off Switch: Set the on/off switch to the “On” position. This switch usually has an “I” (On) and “O” (Off) symbol.
  • Primer Bulb: Press the primer bulb several times until you see fuel filling the bulb, usually 5 to 6 times.
  • Choke: Set the choke lever to the closed position. This is usually achieved by moving the choke lever downwards.
  • Throttle Lock: Engage the throttle lock by pressing the throttle trigger lockout and squeezing the throttle trigger fully. This locks the throttle in the open position.
  • Start Position: With the saw on the ground, place your left foot on the rear handle to stabilize the chainsaw. Hold the top handle with your left hand and pull the starter rope slowly until you feel resistance. This is the point where the engine is about to fire.
  • Pull the Starter Rope: Give a quick, strong pull to start the engine. The engine should sputter and start to run for a moment.
  • Move to Run Position: After the engine sputters, move the choke lever to the half-open position (midway between closed and open). This helps the engine transition from a cold start to running smoothly.
  • Idle: If the engine starts, disengage the throttle lock and let the engine idle for a moment. The chain should not be moving at this point.
  • Warm Up: Allow the chainsaw to warm up for a minute or so before using it. During this time, the engine should stabilize, and you can disengage the choke fully when the engine is running smoothly.
  • Release Chain Brake: Before starting to cut, release the chain brake by pulling the front hand guard towards you. This allows the chain to rotate.

Also remember, this is a general guide. Must consult your Stihl MS 170 chainsaw’s user manual for specific instructions and safety precautions. If you’re not comfortable starting the chainsaw or if you’re unfamiliar with its operation, it’s recommended to seek assistance from a knowledgeable person or professional.

Stihl MS170 Won’t Start – FAQs

Why won't my chainsaw start if I have a spark?
If your chainsaw has a spark but still won’t start, it indicates that while the ignition system is working correctly, there might be issues with other critical factors such as the fuel mixture, compression, or air intake. Chainsaws require a combination of these elements for proper combustion and ignition. If any of these factors are not within the correct parameters, the chainsaw may not start even if there is a spark.
What to check when the chainsaw won t start?
When troubleshooting a chainsaw that won’t start, consider checking the following: Fuel quality and mixture. Air filter for clogs. Compression levels in the engine. Carburetor for clogs or adjustments. Spark plug condition. Proper priming and choke usage. Exhaust and muffler for blockages. Ignition system functionality. Adherence to safety features. Following the manufacturer’s starting procedures.
How do you prime a Stihl MS170?
To prime a Stihl MS170 chainsaw, follow these steps: Locate the primer bulb on the side of the chainsaw’s engine. Press the primer bulb several times until you see fuel filling the bulb. Usually, 5 to 6 presses are sufficient. The primer bulb helps draw fuel into the carburetor, assisting with starting by providing the engine with a fuel-rich mixture.
What would cause a STIHL chainsaw not to start?
Several factors can cause an STIHL chainsaw not to start: Incorrect fuel mixture or poor-quality fuel. Clogged or dirty air filter. Low compression due to worn components. Carburetor issues such as clogs or adjustments. Fouled or worn spark plug. Incorrect use of the choke or throttle. Obstructed exhaust or muffler. Malfunctioning ignition system. Problems with safety mechanisms. Failure to follow proper starting procedures. <span style="font-weight: 400;">Remember, proper maintenance, adhering to safety guidelines, and using quality fuel are essential for the reliable operation of your chainsaw. If troubleshooting doesn’t resolve the issue, seeking assistance from a professional chainsaw technician is recommended.</span>



Encountering Starting issues with your STIHL MS 170 chainsaw can be frustrating. But with the knowledge of potential causes and the solution steps outlined in this guide, you’re well-equipped to address the problem. Regular maintenance and adherence to manufacturer guidelines for fuel mixture ratios and usage can significantly reduce the likelihood of encountering such issues. Here are some of the chainsaw tips for beginners, must read it once to clear your confusion. 

We also have some other options for you, if you want something extraordinary. Check our article on the best Stihl chainsaws and best Chainsaw brands, This will help you a lot in making up your mind and finding the chainsaw that suits you the best. 

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