Stihl MS 170 Wont Start (5 Proven Fixes for Arborists)
Let’s face it, in our quest for smart living – whether it’s heating our homes efficiently with a wood stove, maintaining a beautiful yard with perfectly pruned trees, or even just enjoying the satisfaction of splitting our own firewood – a reliable chainsaw is indispensable. And when that chainsaw, especially a trusty Stihl MS 170, decides it doesn’t want to play ball, it can throw a wrench into even the most well-laid plans. I’ve been there, staring at a silent saw, wondering what went wrong. Over years spent felling trees, processing timber, and prepping firewood, I’ve learned that a non-starting MS 170 isn’t necessarily a death sentence. More often than not, it’s a problem with a relatively simple fix.
That’s why I’ve put together this guide, “Stihl MS 170 Won’t Start: 5 Proven Fixes for Arborists (and You!).” I’m not just going to tell you what to do; I’m going to explain why you’re doing it, giving you the knowledge to diagnose and resolve these issues yourself. Think of this as your personal troubleshooting manual, drawing from my own experiences and insights.
Diagnosing the Silent Saw: Why Your Stihl MS 170 Won’t Start
Before we dive into specific fixes, it’s crucial to understand the underlying reasons why your MS 170 might be refusing to start. We’re dealing with a small engine here, and its functionality relies on a delicate balance of fuel, air, and spark.
- Fuel Delivery Issues: This is one of the most common culprits. A dirty carburetor, a clogged fuel filter, or stale fuel can all prevent the engine from getting the fuel it needs.
- Ignition Problems: Without a spark, there’s no combustion. A faulty spark plug, a damaged ignition coil, or a short in the wiring can all be the cause.
- Compression Loss: The engine needs compression to ignite the fuel-air mixture. A worn piston ring or a leaky cylinder head gasket can lead to a loss of compression.
- Airflow Obstructions: A blocked air filter can choke the engine, preventing it from getting the necessary air for combustion.
- Flooding: Too much fuel in the cylinder can also prevent the engine from starting.
Key Concepts: Fuel, Air, Spark, and Compression
Let’s break down these concepts further.
- Fuel: The MS 170, like most chainsaws, runs on a mixture of gasoline and two-stroke oil. The oil lubricates the engine’s internal components. Using the wrong fuel mixture (too much or too little oil) can damage the engine. I always recommend using a high-quality two-stroke oil specifically designed for air-cooled engines and following the manufacturer’s recommended mixing ratio (usually 50:1). Stale fuel can also be a problem. Gasoline degrades over time, especially when mixed with oil. I typically use fuel stabilizer if I know the saw will be sitting for more than a month.
- Air: The engine needs a clean supply of air for efficient combustion. The air filter prevents dust and debris from entering the engine. A clogged air filter restricts airflow, leading to a weak or non-existent start.
- Spark: The spark plug creates the spark that ignites the fuel-air mixture. A fouled or damaged spark plug won’t produce a spark, preventing the engine from starting.
- Compression: The piston’s movement inside the cylinder compresses the fuel-air mixture, making it easier to ignite. A loss of compression means the mixture won’t ignite properly.
5 Proven Fixes for a Non-Starting Stihl MS 170
Now, let’s get down to the practical solutions. These fixes are presented in order of complexity, starting with the easiest and most common issues.
Fix #1: Check and Replace the Spark Plug
This is often the first place I look when a chainsaw refuses to start. It’s a simple check and a relatively inexpensive fix.
Tools You’ll Need:
- Spark plug wrench (usually comes with the chainsaw)
- New spark plug (Stihl recommends a specific spark plug for the MS 170 – check your manual)
- Wire brush (optional, for cleaning the old spark plug if you want to try reusing it)
Step-by-Step Guide:
- Safety First: Disconnect the spark plug wire from the spark plug. This prevents accidental starting while you’re working on it.
- Locate the Spark Plug: The spark plug is usually located on the side of the engine, under a rubber boot.
- Remove the Spark Plug: Use the spark plug wrench to loosen and remove the spark plug.
- Inspect the Spark Plug: Examine the spark plug for signs of damage, fouling (carbon buildup), or excessive wear. A healthy spark plug should have a clean, dry electrode.
- Clean (Optional): If the spark plug is just slightly fouled, you can try cleaning it with a wire brush. However, I generally recommend replacing it.
- Gap the New Spark Plug: Use a spark plug gapping tool to ensure the gap between the electrode and the ground strap is correct. The correct gap for the Stihl MS 170 is usually around 0.5mm (0.020 inches). This measurement can be found in your owner’s manual.
- Install the New Spark Plug: Carefully thread the new spark plug into the cylinder head by hand. Once it’s snug, tighten it with the spark plug wrench. Don’t overtighten!
- Reconnect the Spark Plug Wire: Push the spark plug wire firmly onto the spark plug.
- Test: Try starting the chainsaw.
Why This Works: A fouled or damaged spark plug can prevent the engine from generating a spark, which is essential for combustion. Replacing the spark plug ensures a strong, consistent spark.
Personal Experience: I remember one time, I was cutting firewood in the middle of winter. My MS 170 suddenly died. I was convinced it was a major problem, but after swapping out the spark plug, it fired right up. It turned out the old spark plug was just heavily fouled due to the cold weather and the engine running rich.
Fix #2: Clean or Replace the Air Filter
A clogged air filter restricts airflow to the engine, leading to a weak or non-existent start. This is especially true if you’re working in dusty or dirty conditions.
Tools You’ll Need:
- Screwdriver (usually a flathead)
- Clean, dry cloth
- Warm water and mild detergent (if cleaning)
- Air compressor (optional, for drying)
- New air filter (if replacing)
Step-by-Step Guide:
- Locate the Air Filter: The air filter is usually located under a cover on the top or side of the engine.
- Remove the Air Filter Cover: Use a screwdriver to remove the air filter cover.
- Remove the Air Filter: Carefully remove the air filter from its housing.
- Inspect the Air Filter: Examine the air filter for dirt, debris, and damage.
- Clean the Air Filter (If Reusable): If the air filter is made of foam or a similar washable material, you can clean it. Wash it in warm water with mild detergent, rinse thoroughly, and allow it to dry completely. I often use an air compressor to speed up the drying process. A paper air filter cannot be cleaned and must be replaced.
- Replace the Air Filter (If Necessary): If the air filter is heavily soiled or damaged, replace it with a new one.
- Clean the Air Filter Housing: Use a clean, dry cloth to wipe out the air filter housing.
- Install the Air Filter: Carefully install the air filter back into its housing. Make sure it’s properly seated.
- Reinstall the Air Filter Cover: Reinstall the air filter cover and tighten the screws.
- Test: Try starting the chainsaw.
Why This Works: Cleaning or replacing the air filter ensures that the engine receives a sufficient supply of clean air for combustion.
Strategic Advantage: Regularly cleaning or replacing the air filter not only improves starting performance but also extends the life of the engine by preventing dirt and debris from entering the combustion chamber. I make it a habit to check the air filter after every few uses, especially when working in dusty conditions.
Fix #3: Check and Clean the Fuel Filter
The fuel filter prevents dirt and debris from entering the carburetor. A clogged fuel filter can restrict fuel flow, leading to a weak or non-existent start.
Tools You’ll Need:
- Small screwdriver or pick
- Clean container
- New fuel filter (recommended)
- Fuel line clamp (optional, but recommended)
Step-by-Step Guide:
- Safety First: Disconnect the spark plug wire from the spark plug.
- Locate the Fuel Filter: The fuel filter is usually located inside the fuel tank, attached to the end of the fuel line.
- Empty the Fuel Tank (Recommended): For ease of access and to prevent fuel spillage, I recommend emptying the fuel tank. You can pour the fuel into a clean container.
- Access the Fuel Filter: Use a small screwdriver or pick to carefully pull the fuel line out of the fuel tank. You may need to use a fuel line clamp to pinch the fuel line and prevent fuel from siphoning out.
- Remove the Fuel Filter: The fuel filter is usually attached to the end of the fuel line. You may need to gently pull it off.
- Inspect the Fuel Filter: Examine the fuel filter for dirt, debris, and damage.
- Replace the Fuel Filter: I always recommend replacing the fuel filter rather than trying to clean it. Fuel filters are relatively inexpensive, and a new filter ensures optimal fuel flow.
- Reinstall the Fuel Filter: Attach the new fuel filter to the end of the fuel line.
- Reinstall the Fuel Line: Carefully reinsert the fuel line back into the fuel tank. Make sure it’s securely attached.
- Refill the Fuel Tank: Refill the fuel tank with fresh fuel.
- Reconnect the Spark Plug Wire: Push the spark plug wire firmly onto the spark plug.
- Test: Try starting the chainsaw.
Why This Works: Replacing the fuel filter ensures that the carburetor receives a clean, unrestricted supply of fuel.
Case Study: I once had a client who was struggling to start his MS 170. He had tried everything he could think of, but nothing seemed to work. I checked the fuel filter and found it completely clogged with debris. After replacing the fuel filter, the chainsaw started on the first pull. He was amazed at how such a small part could cause so much trouble.
Fix #4: Clean the Carburetor
The carburetor mixes air and fuel to create the combustible mixture that powers the engine. A dirty or clogged carburetor can disrupt this mixture, leading to starting problems. This is a more involved process but often necessary.
Tools You’ll Need:
- Screwdrivers (various sizes)
- Carburetor cleaner spray
- Compressed air (optional, but recommended)
- Small brushes or pipe cleaners
- Carburetor rebuild kit (optional, but recommended if the carburetor is heavily soiled or damaged)
- Clean workspace
Step-by-Step Guide:
- Safety First: Disconnect the spark plug wire from the spark plug.
- Remove the Air Filter and Air Filter Housing: As described in Fix #2.
- Disconnect Fuel Lines: Carefully disconnect the fuel lines from the carburetor. Use a fuel line clamp to prevent fuel spillage. Note the position of each fuel line before disconnecting them.
- Remove the Carburetor: Remove the screws or bolts that hold the carburetor in place. Carefully remove the carburetor from the engine.
- Disassemble the Carburetor: This is where things get a bit more complex. I recommend taking pictures or videos as you disassemble the carburetor so you can remember how everything goes back together. Carefully remove the various components of the carburetor, such as the fuel bowl, jets, needles, and diaphragms.
- Clean the Carburetor Components: Spray all the carburetor components with carburetor cleaner. Use small brushes or pipe cleaners to remove any dirt or debris. Pay particular attention to the jets and needles, as these are easily clogged.
- Blow Out Passages with Compressed Air: Use compressed air to blow out all the passages in the carburetor body. This will help to remove any remaining dirt or debris.
- Reassemble the Carburetor: Carefully reassemble the carburetor, referring to your pictures or videos as needed. Make sure all the components are properly seated. If you’re using a carburetor rebuild kit, replace any worn or damaged parts.
- Reinstall the Carburetor: Reinstall the carburetor onto the engine, making sure it’s securely attached.
- Reconnect Fuel Lines: Reconnect the fuel lines to the carburetor, making sure they’re connected to the correct ports.
- Reinstall the Air Filter and Air Filter Housing: As described in Fix #2.
- Reconnect the Spark Plug Wire: Push the spark plug wire firmly onto the spark plug.
- Adjust the Carburetor (If Necessary): After cleaning the carburetor, you may need to adjust the idle speed and the high-speed mixture. Refer to your owner’s manual for instructions on how to adjust the carburetor.
- Test: Try starting the chainsaw.
Why This Works: Cleaning the carburetor removes any dirt or debris that may be blocking the fuel passages, allowing the engine to receive the correct fuel-air mixture.
Technical Details: Carburetors are precision instruments. The jets, for example, have very small orifices that can easily be clogged. Even a tiny amount of dirt can disrupt the fuel flow and prevent the engine from starting. The MS 170 carburetor typically has an idle jet, a main jet, and a needle valve. The idle jet controls the fuel flow at idle, the main jet controls the fuel flow at high speed, and the needle valve adjusts the fuel-air mixture.
Personalized Story: I once spent an entire afternoon trying to get a chainsaw to start. I had checked everything I could think of, but nothing seemed to work. Finally, I decided to take apart the carburetor. I found that one of the jets was completely clogged with varnish from old fuel. After cleaning the jet, the chainsaw started right up. That experience taught me the importance of using fresh fuel and properly storing my chainsaws when they’re not in use.
Fix #5: Check Compression
If all the other fixes have failed, the problem may be a loss of compression. This is a more serious issue that may require professional repair.
Tools You’ll Need:
- Compression tester
- Spark plug wrench
Step-by-Step Guide:
- Safety First: Disconnect the spark plug wire from the spark plug.
- Remove the Spark Plug: Use the spark plug wrench to remove the spark plug.
- Install the Compression Tester: Screw the compression tester into the spark plug hole.
- Test Compression: Pull the starter cord several times while watching the compression gauge.
- Check Compression Reading: The compression reading should be within the manufacturer’s specifications. For the Stihl MS 170, the compression should typically be around 120-150 PSI.
- Interpret Results: A low compression reading indicates a potential problem with the piston rings, cylinder, or valves.
Why This Works: Compression is essential for the engine to ignite the fuel-air mixture. A loss of compression means the mixture won’t ignite properly.
When to Seek Professional Help: If the compression reading is significantly below the manufacturer’s specifications, it’s best to take the chainsaw to a qualified repair technician. They can diagnose the problem and recommend the necessary repairs. Common causes of compression loss include worn piston rings, a scored cylinder, or a leaky cylinder head gasket.
Preventive Maintenance: Keeping Your Stihl MS 170 Running Smoothly
The best way to avoid starting problems is to perform regular preventive maintenance. Here are some tips:
- Use Fresh Fuel: Always use fresh fuel and mix it with the correct amount of two-stroke oil. I recommend using fuel stabilizer if you know the saw will be sitting for more than a month.
- Clean the Air Filter Regularly: Clean the air filter after every few uses, especially when working in dusty conditions.
- Replace the Fuel Filter Annually: Replace the fuel filter at least once a year, or more often if you’re using the chainsaw frequently.
- Inspect the Spark Plug Regularly: Inspect the spark plug regularly and replace it when necessary.
- Store the Chainsaw Properly: When storing the chainsaw for an extended period, drain the fuel tank and run the engine until it stalls. This will prevent the carburetor from becoming clogged with varnish.
- Sharpen the Chain Regularly: A sharp chain makes the chainsaw easier to start and reduces strain on the engine.
- Lubricate the Chain Regularly: Keep the chain properly lubricated to prevent wear and tear.
- Follow the Manufacturer’s Recommendations: Always follow the manufacturer’s recommendations for maintenance and operation.
Strategic Advantage: Proactive maintenance not only prevents starting problems but also extends the life of your chainsaw and improves its overall performance. It’s an investment that pays off in the long run.
Wood Processing & Firewood Preparation: The Importance of a Reliable Chainsaw
In the world of wood processing and firewood preparation, a reliable chainsaw is more than just a tool; it’s a partner. Whether you’re felling trees for timber, bucking logs for firewood, or pruning branches in your yard, a chainsaw is essential.
- Felling Techniques: Proper felling techniques are crucial for safety and efficiency. I always recommend using a felling wedge to prevent the tree from pinching the chainsaw bar. The size of the wedge depends on the diameter of the tree. For a tree with a diameter of 12 inches, I would use a wedge that is at least 6 inches long.
- Bucking Logs: Bucking logs into firewood requires precision and skill. I always recommend using a log stand to elevate the log and prevent the chainsaw from hitting the ground. The length of the firewood depends on the size of your wood stove or fireplace. A standard length is 16 inches.
- Debarking Logs: Debarking logs can be done manually with a drawknife or mechanically with a debarker. Debarking logs helps to speed up the drying process and prevent insect infestations.
- Splitting Firewood: Splitting firewood can be done manually with an axe or mechanically with a log splitter. A hydraulic log splitter can significantly increase efficiency, especially when dealing with large or knotty logs. I use a 25-ton hydraulic log splitter, which can split logs up to 24 inches in diameter.
- Drying Methods: Drying firewood is essential for efficient burning. Green wood has a high moisture content, which makes it difficult to ignite and produces a lot of smoke. Seasoned wood, on the other hand, has a low moisture content and burns cleanly. I recommend drying firewood for at least six months, or longer if possible. The ideal moisture content for firewood is around 20%.
- Firewood Stacking: Proper firewood stacking is important for air circulation and drying. I recommend stacking firewood in a single row, with the pieces slightly spaced apart. This allows air to circulate around the wood and helps it to dry more quickly.
Wood Type Selection:
Different types of wood have different burning characteristics. Hardwoods, such as oak, maple, and ash, are denser and burn longer than softwoods, such as pine, fir, and spruce. However, softwoods are easier to ignite and produce more heat. I typically use a mixture of hardwoods and softwoods for my firewood. The hardwoods provide long-lasting heat, while the softwoods help to get the fire started quickly.
Safety Considerations:
Safety is paramount when working with chainsaws and wood processing equipment. Always wear appropriate personal protective equipment (PPE), including a helmet, eye protection, hearing protection, gloves, and chainsaw chaps. Be aware of your surroundings and avoid working in hazardous conditions. Never operate a chainsaw when you’re tired or under the influence of drugs or alcohol.
Conclusion: Empowering You to Keep Your Saw Running
A non-starting Stihl MS 170 can be frustrating, but with a little knowledge and some basic troubleshooting skills, you can often fix the problem yourself. By following the steps outlined in this guide, you can diagnose the issue, implement the appropriate fix, and get your chainsaw back up and running. Remember to prioritize safety and perform regular preventive maintenance to keep your chainsaw running smoothly for years to come.
Next Steps:
- Identify the Problem: Use the troubleshooting tips in this guide to diagnose the reason why your Stihl MS 170 won’t start.
- Gather Your Tools and Supplies: Gather the necessary tools and supplies for the fix you’ve identified.
- Follow the Step-by-Step Guide: Carefully follow the step-by-step guide to implement the fix.
- Test Your Chainsaw: After completing the fix, test your chainsaw to see if it starts.
- Perform Regular Maintenance: Perform regular preventive maintenance to keep your chainsaw running smoothly.
By taking these steps, you can ensure that your Stihl MS 170 is always ready to tackle your wood processing and firewood preparation needs. Happy cutting!
