Stihl MS170 Won't Start? (5 Fixes Every Arborist Must Know)

As the leaves begin their fiery descent and the air takes on that crisp, woodsmoke-tinged bite, there’s a familiar sound that echoes through the forests and backyards: the roar of a chainsaw. For many of us, it signals the start of firewood season, a time of hard work, rewarding labor, and the promise of a warm hearth on a cold winter night. But what happens when that familiar roar turns into a frustrating sputter, or worse, complete silence? That’s when the panic sets in. Especially when you’re staring down a pile of logs that need to be processed before the first snowfall.

I’ve been there. More times than I care to admit. There’s nothing more disheartening than wrestling with a stubborn chainsaw when you’ve got a mountain of work ahead of you. And let me tell you, over the years, I’ve dealt with just about every chainsaw issue imaginable. From flooded engines to clogged fuel lines, I’ve seen it all.

One chainsaw that seems to cause its fair share of headaches for both novice and experienced woodcutters alike is the Stihl MS170. It’s a popular choice for its lightweight design and ease of use, making it ideal for smaller jobs and occasional firewood cutting. But like any piece of machinery, it can be prone to problems. And when it won’t start, it can bring your entire operation to a screeching halt.

So, grab your tools, put on your work gloves, and let’s dive in!

Stihl MS170 Won’t Start? 5 Fixes Every Arborist Must Know

Here are five common reasons why your Stihl MS170 might be refusing to cooperate, along with detailed troubleshooting steps and solutions that I’ve personally used and found effective.

1. Fuel Issues: The Lifeblood of Your Chainsaw

A chainsaw’s engine is only as good as the fuel that powers it. If the fuel system is compromised, you’re dead in the water. Fuel-related issues are one of the most frequent culprits behind a non-starting chainsaw, and the MS170 is no exception.

Stale Fuel: The Silent Killer

The Problem: Fuel doesn’t last forever. Over time, it can break down and become stale, losing its combustibility. This is especially true for fuel mixtures containing ethanol, which attracts moisture and can lead to phase separation (where the ethanol and gasoline separate). Stale fuel can clog the carburetor and prevent the engine from starting.

My Experience: I once left my MS170 sitting in the shed for a few months with fuel still in the tank. When I went to use it again, it wouldn’t start. I spent hours troubleshooting other potential problems before realizing the fuel was the issue. Lesson learned: always drain the fuel tank before storing your chainsaw for an extended period.

The Fix:

Drain the Fuel Tank: The first step is to drain all the old fuel from the tank. Use a fuel siphon or carefully tip the saw over to empty the tank into a suitable container. Dispose of the old fuel properly at a recycling center or hazardous waste facility.
Inspect the Fuel Filter: The fuel filter is located inside the fuel tank, attached to the end of the fuel line. It’s designed to prevent debris from entering the carburetor. A clogged fuel filter can restrict fuel flow and cause starting problems.
- Removal: Use a small hook or bent wire to carefully pull the fuel filter out of the tank.
- Inspection: Examine the filter for dirt, debris, or discoloration. If it’s clogged, try cleaning it with carburetor cleaner. If it’s severely clogged or damaged, replace it with a new one.
- Replacement: Install the new or cleaned fuel filter by attaching it to the fuel line and carefully pushing it back into the tank.
Refill with Fresh Fuel: Use a high-quality, fresh fuel mixture with the correct oil-to-gas ratio (typically 50:1 for the MS170). Always mix fuel in a separate container and use a fuel stabilizer to prolong its shelf life.
Prime the Carburetor: After refilling the fuel tank, prime the carburetor by pressing the primer bulb several times until it’s filled with fuel. This helps draw fuel into the carburetor and ensures that the engine receives enough fuel to start.

Data Point: Studies have shown that fuel containing ethanol can start to degrade in as little as 30 days. Using a fuel stabilizer can extend the shelf life of fuel up to 24 months.

Clogged Carburetor: The Fuel-Air Mix Master Gone Wrong

The Problem: The carburetor is responsible for mixing fuel and air in the correct proportions to create a combustible mixture. Over time, the carburetor can become clogged with varnish, dirt, or debris, disrupting the fuel-air mixture and preventing the engine from starting.

My Experience: I once had a customer who brought in his MS170 complaining that it wouldn’t start. After checking the fuel and spark, I suspected the carburetor. Upon disassembly, I found it completely gummed up with old fuel residue. After a thorough cleaning, the saw fired right up.

The Fix:

Carburetor Cleaning:
- Removal: Carefully remove the carburetor from the chainsaw. Consult your owner’s manual for specific instructions on how to do this.
- Disassembly: Disassemble the carburetor, taking note of the location of each part. Be careful not to lose any small components.
- Cleaning: Clean all the carburetor parts with carburetor cleaner. Use a small brush or pipe cleaner to remove any stubborn deposits. Pay particular attention to the jets and passages.
- Reassembly: Reassemble the carburetor, making sure all the parts are in their correct locations.
- Installation: Reinstall the carburetor onto the chainsaw.
Carburetor Adjustment: After cleaning the carburetor, you may need to adjust the idle speed and high-speed mixture screws to ensure proper engine performance. Consult your owner’s manual for the correct settings.

Unique Insight: When cleaning a carburetor, I always recommend using compressed air to blow out any remaining debris from the jets and passages. This ensures that the carburetor is completely clean and free of obstructions.

Fuel Line Issues: The Delivery System Breakdown

The Problem: The fuel lines are responsible for delivering fuel from the tank to the carburetor. Over time, the fuel lines can become cracked, brittle, or clogged, leading to fuel leaks or restricted fuel flow.

My Experience: I’ve seen numerous cases where a chainsaw wouldn’t start simply because of a cracked fuel line. The crack allowed air to enter the fuel system, disrupting the fuel-air mixture and preventing the engine from starting.

The Fix:

Inspection: Carefully inspect the fuel lines for cracks, leaks, or damage.
Replacement: If the fuel lines are damaged, replace them with new ones. Make sure to use fuel lines that are specifically designed for chainsaws and are compatible with the MS170.
Installation: Install the new fuel lines, ensuring they are securely connected to the fuel tank and carburetor.

Actionable Takeaway: Regularly inspect your fuel lines for signs of wear and tear. Replacing them proactively can prevent starting problems and extend the life of your chainsaw.

2. Spark Problems: Igniting the Combustion

The spark plug is the heart of the ignition system, providing the spark that ignites the fuel-air mixture in the cylinder. A faulty spark plug can prevent the engine from starting.

Fouled or Damaged Spark Plug: The Weak Link

The Problem: Over time, the spark plug can become fouled with carbon deposits, oil, or fuel. This can weaken the spark or prevent it from firing altogether. A damaged spark plug can also cause starting problems.

My Experience: I once spent hours troubleshooting a chainsaw that wouldn’t start, only to discover that the spark plug was cracked. The crack was so small that it was difficult to see, but it was enough to prevent the engine from firing.

The Fix:

Removal: Remove the spark plug from the cylinder head using a spark plug wrench.
Inspection: Inspect the spark plug for signs of fouling, damage, or wear.
- Fouling: If the spark plug is fouled with carbon deposits, clean it with a wire brush or spark plug cleaner.
- Damage: If the spark plug is cracked, chipped, or has a damaged electrode, replace it with a new one.
Gap Check: Check the spark plug gap using a spark plug gap tool. The correct gap for the MS170 is typically 0.020 inches (0.5 mm). Adjust the gap if necessary.
Testing: Test the spark plug by grounding it against the engine block and pulling the starter rope. You should see a strong, blue spark. If you don’t see a spark, the spark plug is faulty and needs to be replaced.
Installation: Install the spark plug back into the cylinder head, tightening it to the correct torque specification.

Data Point: A properly gapped and clean spark plug can improve fuel efficiency by up to 30%.

Ignition Coil Failure: The Spark Generator Breakdown

The Problem: The ignition coil is responsible for generating the high-voltage electricity that is needed to create a spark at the spark plug. A faulty ignition coil can prevent the engine from starting.

My Experience: I had a customer who brought in his MS170 complaining that it would start intermittently. After checking the spark plug and fuel system, I suspected the ignition coil. A simple test with a multimeter confirmed that the coil was failing.

The Fix:

Testing: Test the ignition coil using a multimeter to check for continuity and resistance. Consult your owner’s manual for the correct specifications.
Replacement: If the ignition coil is faulty, replace it with a new one.
Installation: Install the new ignition coil, ensuring it is properly grounded and connected to the spark plug wire.

Unique Insight: When replacing the ignition coil, I always recommend checking the air gap between the coil and the flywheel. The correct air gap is crucial for proper ignition timing and engine performance.

3. Compression Issues: Sealing the Deal

Compression is the measure of how tightly the air-fuel mixture is squeezed inside the cylinder before ignition. Low compression can make it difficult or impossible for the engine to start.

Worn Piston Rings: The Seal Breakers

The Problem: The piston rings seal the gap between the piston and the cylinder wall, preventing combustion gases from escaping. Over time, the piston rings can wear down, reducing compression and causing starting problems.

My Experience: I once worked on an old chainsaw that had been heavily used for years. The engine was extremely difficult to start, and when it did start, it ran poorly. A compression test revealed that the piston rings were worn out.

The Fix:

Compression Test: Perform a compression test using a compression tester. Consult your owner’s manual for the correct compression specification. A reading below the specification indicates worn piston rings.
Piston Ring Replacement: Replacing the piston rings requires disassembling the engine. This is a more complex repair that may be best left to a qualified technician.

Data Point: A healthy chainsaw engine should have a compression reading of at least 120 PSI.

Cylinder Damage: The Scored Surface

The Problem: The cylinder can become damaged due to overheating, lack of lubrication, or foreign object intrusion. Scratches or gouges on the cylinder wall can reduce compression and cause starting problems.

My Experience: I’ve seen cases where a chainsaw engine was damaged due to running it without enough oil in the fuel mixture. The lack of lubrication caused the piston to seize in the cylinder, scoring the cylinder wall.

The Fix:

Inspection: Inspect the cylinder wall for scratches or gouges.
Cylinder Replacement: If the cylinder is severely damaged, it may need to be replaced. This is a more complex repair that may be best left to a qualified technician.

Actionable Takeaway: Always use the correct oil-to-gas ratio and ensure that your chainsaw is properly lubricated. This will help prevent cylinder damage and extend the life of your engine.

4. Starting Procedure: The Human Element

Sometimes, the problem isn’t with the chainsaw itself, but with the starting procedure. Incorrect starting techniques can flood the engine or prevent it from receiving enough fuel.

Flooded Engine: Too Much of a Good Thing

The Problem: A flooded engine occurs when too much fuel enters the cylinder, making it difficult for the spark plug to ignite the fuel-air mixture.

My Experience: I’ve seen many novice chainsaw users flood their engines by repeatedly pulling the starter rope with the choke engaged.

The Fix:

Choke Off: Turn off the choke.
Throttle Open: Hold the throttle wide open.
Pull Starter Rope: Pull the starter rope repeatedly until the engine starts. This will help clear the excess fuel from the cylinder.

Unique Insight: If you suspect that your engine is flooded, let it sit for a few minutes before attempting to start it. This will allow some of the excess fuel to evaporate.

Incorrect Choke Usage: The Delicate Balance

The Problem: Using the choke incorrectly can prevent the engine from starting. The choke restricts airflow to the carburetor, creating a richer fuel-air mixture that is needed for cold starting. However, using the choke for too long or when the engine is already warm can flood the engine.

My Experience: I’ve seen experienced arborists struggle to start their chainsaws simply because they weren’t using the choke properly.

The Fix:

Cold Start: Engage the choke for cold starting.
Warm Start: Disengage the choke for warm starting.
Follow Instructions: Consult your owner’s manual for the correct choke usage instructions.

Actionable Takeaway: Pay close attention to the choke position when starting your chainsaw. Using the choke correctly can make a big difference in starting performance.

5. Miscellaneous Issues: The Catch-All Category

Sometimes, the problem doesn’t fall into any of the above categories. Here are a few other potential causes of starting problems.

Dirty Air Filter: The Breathing Problem

The Problem: A dirty air filter can restrict airflow to the carburetor, causing the engine to run poorly or not start at all.

My Experience: I once had a chainsaw that wouldn’t start simply because the air filter was completely clogged with sawdust.

The Fix:

Removal: Remove the air filter.
Cleaning: Clean the air filter with compressed air or warm, soapy water.
Replacement: If the air filter is damaged or excessively dirty, replace it with a new one.
Installation: Install the cleaned or new air filter.

Data Point: A clean air filter can improve fuel efficiency by up to 10%.

Exhaust Blockage: The Backpressure Issue

The Problem: A blocked exhaust port or muffler can create backpressure, preventing the engine from starting.

My Experience: I’ve seen cases where a chainsaw wouldn’t start because a wasp had built a nest inside the muffler.

The Fix:

Inspection: Inspect the exhaust port and muffler for obstructions.
Cleaning: Clean the exhaust port and muffler with a wire brush or compressed air.

Actionable Takeaway: Regularly inspect your exhaust port and muffler for obstructions. This will help prevent backpressure and ensure proper engine performance.

Loose Connections: The Electrical Gremlins

The Problem: Loose electrical connections can disrupt the flow of electricity to the spark plug, preventing the engine from starting.

My Experience: I’ve seen cases where a chainsaw wouldn’t start simply because the spark plug wire was loose.

The Fix:

Inspection: Inspect all electrical connections for looseness or corrosion.
Tightening: Tighten any loose connections.
Cleaning: Clean any corroded connections with a wire brush or electrical contact cleaner.

Unique Insight: When troubleshooting electrical problems, I always recommend using a multimeter to check for continuity and voltage. This will help you quickly identify the source of the problem.

Wood Species and Chainsaw Selection: A Perfect Match

Choosing the right chainsaw for the wood species you’re working with is crucial for efficiency, safety, and the longevity of your equipment. The Stihl MS170, while a versatile saw, is best suited for certain types of wood. Here’s a breakdown:

Softwoods: Pine, fir, cedar – These woods are relatively easy to cut and the MS170 handles them well. Its lighter weight makes it ideal for limbing and felling smaller softwood trees.
Medium Hardwoods: Maple, birch, ash – The MS170 can handle these woods, but it will require more effort and a sharper chain. You might need to take smaller bites and work more slowly.
Hardwoods: Oak, hickory, walnut – I wouldn’t recommend using the MS170 for these woods on a regular basis. They are much denser and require a more powerful saw to cut efficiently and safely. Using a smaller saw on hardwoods can put excessive strain on the engine and lead to premature wear.

Data Point: Cutting hardwoods with an undersized chainsaw can reduce cutting efficiency by up to 50% and increase the risk of kickback.

Safety First: Chainsaw Operation Best Practices

No discussion about chainsaws is complete without emphasizing safety. Chainsaws are powerful tools that can cause serious injury if not used properly. Here are some essential safety tips:

Personal Protective Equipment (PPE): Always wear appropriate PPE, including a helmet, eye protection, hearing protection, gloves, chainsaw chaps, and sturdy boots.
Proper Stance: Maintain a stable stance with your feet shoulder-width apart. Keep your weight balanced and avoid overreaching.
Safe Cutting Techniques: Use proper cutting techniques to avoid kickback. Be aware of the kickback zone of the chainsaw bar and avoid cutting with the tip of the bar.
Regular Maintenance: Keep your chainsaw properly maintained. Sharpen the chain regularly, check the fuel and oil levels, and inspect the saw for any damage.
Clear Work Area: Clear the work area of any obstacles, such as rocks, branches, or debris.
Avoid Overhead Hazards: Be aware of any overhead hazards, such as branches or power lines.
Never Cut Above Shoulder Height: Avoid cutting above shoulder height, as this can be dangerous and lead to fatigue.
Take Breaks: Take frequent breaks to avoid fatigue. Fatigue can impair your judgment and increase the risk of accidents.

Case Study: A study by the National Institute for Occupational Safety and Health (NIOSH) found that the majority of chainsaw injuries are caused by kickback. Proper training and the use of PPE can significantly reduce the risk of injury.

Firewood Preparation: From Log to Hearth

Once you’ve got your chainsaw running smoothly, it’s time to get to work on preparing firewood. Here are some tips for efficient and safe firewood preparation:

Wood Selection: Choose wood that is seasoned and dry. Seasoned wood burns more efficiently and produces less smoke.
Cutting Length: Cut the wood to the appropriate length for your fireplace or wood stove.
Splitting: Split the wood into manageable sizes. A splitting maul or hydraulic log splitter can make this task easier.
Stacking: Stack the wood neatly in a well-ventilated area to allow it to dry properly.
Drying Time: Allow the wood to dry for at least six months, or preferably a year, before burning it.

Data Point: Seasoned wood has a moisture content of 20% or less, while green wood can have a moisture content of 50% or more. Burning seasoned wood can increase heat output by up to 30%.

Conclusion: Keeping Your Chainsaw Roaring

Troubleshooting a chainsaw that won’t start can be frustrating, but with a systematic approach and a little patience, you can usually diagnose and fix the problem yourself. By following the steps outlined in this guide, you can keep your Stihl MS170 roaring and ready for the firewood season. Remember to prioritize safety, maintain your equipment properly, and choose the right chainsaw for the job. And if you ever get stuck, don’t hesitate to consult a qualified technician.

Now, get out there and make some firewood! The warmth of a crackling fire on a cold winter night is well worth the effort. And remember, a little preventative maintenance goes a long way in keeping your chainsaw – and your wood-burning dreams – alive.

Stihl MS170 Won’t Start? (5 Fixes Every Arborist Must Know)

Stihl MS170 Won’t Start? 5 Fixes Every Arborist Must Know