Stihl M170 Chainsaw Troubleshooting Tips (5 Expert Fixes)

Stihl MS170 Chainsaw Troubleshooting Tips (5 Expert Fixes)

Here in the Pacific Northwest, where I’ve spent the better part of my life felling trees and preparing firewood, a reliable chainsaw is as essential as a good pair of boots. The Stihl MS170 is a popular choice for homeowners and occasional users due to its lightweight design and ease of use. However, like any machine, it can encounter problems. I’ve seen firsthand how frustrating it can be when your chainsaw refuses to cooperate, especially when you’re racing against the setting sun to get that woodpile stacked before winter hits. Over the years, I’ve learned to diagnose and fix common issues with the MS170, often right in the field. This guide shares those experiences and provides practical solutions to get your Stihl MS170 back up and running.

Key Concepts: Green Wood vs. Seasoned Wood

Before diving into troubleshooting, let’s define some key terms. Green wood is freshly cut wood that still contains a high moisture content, typically above 30%. It’s heavier and harder to split than seasoned wood. Seasoned wood, on the other hand, has been dried for a period (typically 6-12 months, depending on the climate and wood species) and has a moisture content of 20% or less. Burning seasoned wood is much more efficient and produces less smoke. Understanding this difference is crucial because cutting green wood can put extra strain on your chainsaw.

1. Chainsaw Starts But Immediately Dies

This is a common problem I’ve encountered countless times. The engine sputters to life, only to die seconds later. It’s often a fuel or air issue.

The Diagnosis:

• Fuel Starvation: The engine isn’t getting enough fuel.
• Airflow Obstruction: The engine isn’t getting enough air.

The Fix:

• Step 1: Check the Fuel Cap Vent. The fuel cap vent allows air into the tank, preventing a vacuum that would stop fuel flow. I remember one particularly cold day in the Cascades, my MS170 kept dying. Turns out, the vent was clogged with ice! Remove the fuel cap and inspect the vent hole. Use a small wire or needle to clear any debris.

  • Tool: Small wire or needle.
  • Measurement: Vent hole diameter is typically around 0.5mm.
  • Strategic Insight: A clogged vent is often overlooked, but it can completely shut down fuel flow.

• Step 2: Inspect the Fuel Filter. The fuel filter, located inside the fuel tank, prevents debris from entering the carburetor. I always advise checking this first. Use a fuel line hook or bent wire to pull the filter out of the tank. If it’s dirty or clogged, replace it.

  • Tool: Fuel line hook or bent wire.
  • Material Spec: Replacement fuel filters are inexpensive and readily available at most hardware stores.
  • Cost: Typically under $10.
  • Strategic Insight: Replacing the fuel filter annually, or more often if you use your chainsaw frequently, is a good preventative measure.

• Step 3: Clean the Air Filter. A dirty air filter restricts airflow to the engine. Remove the air filter cover and inspect the filter. If it’s dirty, clean it with warm, soapy water. Allow it to dry completely before reinstalling. If it’s heavily soiled or damaged, replace it.

  • Tool: Warm water, mild soap.
  • Drying Method: Air dry completely before reinstalling.
  • Strategic Insight: Cleaning the air filter regularly, especially when cutting in dusty conditions, will improve engine performance and prolong the life of your chainsaw.

• Step 4: Check the Spark Plug. A fouled spark plug can also cause starting problems. Remove the spark plug and inspect it. If it’s wet, dirty, or damaged, clean or replace it. Ensure the spark plug gap is correct.

  • Tool: Spark plug wrench, feeler gauge.
  • Measurement: Spark plug gap for the Stihl MS170 is typically 0.5mm.
  • Strategic Insight: A properly gapped spark plug ensures a strong spark for reliable ignition.

• Step 5: Carburetor Adjustment (If Necessary). If the above steps don’t solve the problem, the carburetor may need adjustment. However, I strongly advise against tinkering with the carburetor unless you have experience. Incorrect adjustments can damage the engine. If you’re unsure, take your chainsaw to a qualified technician.

  • Tool: Carburetor adjustment tool (specialized tool).
  • Skill Level: Advanced.
  • Caution: Improper carburetor adjustment can lead to engine damage.

Case Study:

I once helped a neighbor whose MS170 kept stalling. He had cleaned the air filter and replaced the spark plug, but the problem persisted. After checking the fuel filter, I found it completely clogged with debris. Replacing the filter solved the problem instantly. This highlights the importance of checking all the potential causes, even the seemingly obvious ones.

2. Chainsaw Won’t Start At All

This is perhaps the most frustrating scenario. You pull the starter cord repeatedly, but the engine refuses to fire.

The Diagnosis:

• No Spark: The engine isn’t receiving a spark to ignite the fuel.
• Flooded Engine: Too much fuel in the cylinder.
• Fuel Delivery Problem: Fuel isn’t reaching the engine.

The Fix:

• Step 1: Check the Spark Plug (Again). Even if you checked it in the previous section, double-check the spark plug. Make sure it’s clean, dry, and properly gapped. Attach the spark plug wire and ground the spark plug against the engine block. Pull the starter cord and look for a strong blue spark. If there’s no spark, replace the spark plug.

  • Tool: Spark plug wrench, feeler gauge.
  • Observation: Look for a strong blue spark.
  • Strategic Insight: A weak or non-existent spark indicates a faulty spark plug or ignition system.

• Step 2: Deflood the Engine. If the engine is flooded, remove the spark plug and pull the starter cord several times to clear excess fuel from the cylinder. Reinstall the spark plug and try starting the chainsaw again.

  • Technique: Pull the starter cord with the choke off.
  • Strategic Insight: Flooding is common when repeatedly trying to start a cold engine.

• Step 3: Check the Ignition Module. The ignition module generates the spark that ignites the fuel. If the spark plug is good but there’s still no spark, the ignition module may be faulty. This is a more complex repair, and I recommend taking your chainsaw to a qualified technician.

  • Skill Level: Advanced.
  • Caution: Working with the ignition module requires specialized knowledge and tools.

• Step 4: Check the Fuel Line. Inspect the fuel line for cracks, leaks, or blockages. A damaged fuel line can prevent fuel from reaching the carburetor. Replace the fuel line if necessary.

  • Tool: Visual inspection.
  • Material Spec: Replacement fuel lines are available at most hardware stores.
  • Strategic Insight: A cracked or brittle fuel line is a common cause of starting problems, especially in older chainsaws.

• Step 5: Check the Carburetor. A clogged carburetor can also prevent the engine from starting. If the fuel filter is clean and the fuel line is intact, the carburetor may need cleaning or rebuilding. This is another complex repair that I recommend leaving to a professional.

  • Skill Level: Advanced.
  • Caution: Carburetor repair requires specialized knowledge and tools.

Personal Experience:

I remember one time, my MS170 refused to start after a particularly wet logging session. I checked everything – spark plug, fuel filter, air filter – but nothing seemed to work. Finally, I discovered that water had entered the fuel tank and contaminated the fuel. Draining the tank and refilling it with fresh fuel solved the problem immediately. This taught me the importance of protecting my chainsaw from the elements.

3. Chainsaw Runs Poorly (Lack of Power, Stalling Under Load)

If your chainsaw starts and runs but lacks power or stalls when cutting, it indicates an issue with fuel-air mixture or engine performance.

The Diagnosis:

• Lean Fuel Mixture: Not enough fuel, too much air.
• Rich Fuel Mixture: Too much fuel, not enough air.
• Worn Piston Rings: Loss of compression.

The Fix:

• Step 1: Check the Air Filter (Again). A dirty air filter restricts airflow, leading to a rich fuel mixture and reduced power. Clean or replace the air filter as described earlier.

  • Tool: Warm water, mild soap.
  • Strategic Insight: Regular air filter maintenance is crucial for optimal engine performance.

• Step 2: Check the Spark Arrestor Screen. The spark arrestor screen, located on the muffler, prevents sparks from escaping and potentially causing fires. A clogged spark arrestor screen restricts exhaust flow, reducing engine power. Remove the spark arrestor screen and clean it with a wire brush.

  • Tool: Wire brush.
  • Strategic Insight: A clogged spark arrestor screen is a common cause of reduced power, especially in older chainsaws.

• Step 3: Carburetor Adjustment (Again, with Caution). If the air filter and spark arrestor screen are clean, the carburetor may need adjustment. As I mentioned before, proceed with caution and only if you have experience. The MS170 usually has two adjustment screws: “H” (high speed) and “L” (low speed).

  • Lean Mixture Adjustment: If the engine is running lean (indicated by high RPMs and a tendency to stall), slightly turn the “L” screw counterclockwise to richen the mixture.
  • Rich Mixture Adjustment: If the engine is running rich (indicated by excessive smoke and poor performance), slightly turn the “L” screw clockwise to lean the mixture.
  • Tool: Carburetor adjustment tool (specialized tool).
  • Skill Level: Advanced.
  • Caution: Make small adjustments and test the chainsaw after each adjustment.

• Step 4: Check for Air Leaks. Air leaks can disrupt the fuel-air mixture and cause poor performance. Inspect the intake manifold and carburetor mounting flange for cracks or loose connections. Replace any damaged parts.

  • Tool: Visual inspection.
  • Strategic Insight: Air leaks can be difficult to diagnose, but they can significantly impact engine performance.

• Step 5: Compression Test. If the above steps don’t solve the problem, the engine may have low compression due to worn piston rings. A compression test can confirm this. However, this requires specialized equipment and knowledge, so I recommend taking your chainsaw to a qualified technician.

  • Tool: Compression tester.
  • Skill Level: Advanced.
  • Caution: A compression test requires specialized equipment and knowledge.

Original Insight:

I’ve found that many performance issues stem from improper chain sharpening. A dull chain forces you to apply more pressure, which can overload the engine and cause it to stall. Regularly sharpen your chain or have it professionally sharpened to maintain optimal cutting performance.

4. Chain Not Oiling Properly

A properly lubricated chain is essential for smooth cutting and preventing premature wear. If the chain isn’t oiling properly, it can lead to overheating, chain damage, and even engine damage.

The Diagnosis:

• Empty Oil Tank: Obvious, but always check first!
• Clogged Oil Filter: Prevents oil from flowing to the chain.
• Blocked Oil Passage: Obstruction in the oil delivery system.
• Faulty Oil Pump: The oil pump isn’t functioning correctly.

The Fix:

• Step 1: Check the Oil Level. Ensure the oil tank is filled with the appropriate chain oil. I prefer using a high-quality bar and chain oil specifically designed for chainsaws.

  • Material Spec: Use high-quality bar and chain oil.
  • Strategic Insight: Using the correct type of oil is crucial for proper lubrication and chain life.

• Step 2: Check the Oil Filter. The oil filter, located inside the oil tank, prevents debris from entering the oil pump. Use a small wire or needle to pull the filter out of the tank and inspect it. If it’s dirty or clogged, clean or replace it.

  • Tool: Small wire or needle.
  • Material Spec: Replacement oil filters are inexpensive and readily available.
  • Strategic Insight: Regular oil filter maintenance is essential for proper chain lubrication.

• Step 3: Clean the Oil Passage. The oil passage delivers oil from the oil pump to the chain. If it’s blocked, the chain won’t receive adequate lubrication. Use a small wire or needle to clear any debris from the oil passage.

  • Tool: Small wire or needle.
  • Strategic Insight: Debris can easily clog the oil passage, especially when cutting dirty wood.

• Step 4: Check the Oil Pump. If the oil filter and oil passage are clear, the oil pump may be faulty. This is a more complex repair, and I recommend taking your chainsaw to a qualified technician.

  • Skill Level: Advanced.
  • Caution: Oil pump repair requires specialized knowledge and tools.

• Step 5: Adjust the Oiler (If Applicable). Some Stihl MS170 models have an adjustable oiler. Check your owner’s manual to see if your model has this feature. If so, adjust the oiler to increase the oil flow to the chain.

  • Tool: Screwdriver (if adjustable).
  • Strategic Insight: Adjusting the oiler can help ensure adequate chain lubrication, especially when cutting hard or dry wood.

Project Example:

I once had a project where I was cutting a large quantity of madrone, a very hard and dense wood. I noticed that my chain was getting excessively hot, even with regular oiling. After inspecting the chainsaw, I discovered that the oil passage was partially blocked with sawdust. Cleaning the oil passage solved the problem and allowed the chain to oil properly.

5. Excessive Vibration

Excessive vibration can be uncomfortable and even dangerous. It can also indicate a problem with the chainsaw.

The Diagnosis:

• Loose Chain: The chain is too loose on the bar.
• Damaged Chain: The chain is damaged or worn.
• Loose Bar: The bar is not properly secured to the chainsaw.
• Worn Anti-Vibration Mounts: The anti-vibration mounts are worn or damaged.

The Fix:

• Step 1: Adjust Chain Tension. A loose chain can cause excessive vibration. Adjust the chain tension according to the manufacturer’s instructions. The chain should fit snugly on the bar but should still be able to be pulled around by hand.

  • Tool: Screwdriver or wrench (depending on model).
  • Strategic Insight: Proper chain tension is crucial for safe and efficient cutting.

• Step 2: Inspect the Chain. A damaged or worn chain can cause excessive vibration. Inspect the chain for broken teeth, cracks, or excessive wear. Replace the chain if necessary.

  • Tool: Visual inspection.
  • Strategic Insight: A damaged chain is not only dangerous but also reduces cutting efficiency.

• Step 3: Tighten the Bar. A loose bar can cause excessive vibration. Ensure the bar is properly secured to the chainsaw. Tighten the bar nuts to the manufacturer’s specifications.

  • Tool: Wrench.
  • Strategic Insight: A loose bar can lead to chain derailment and potential injury.

• Step 4: Inspect Anti-Vibration Mounts. The anti-vibration mounts are designed to absorb vibration and reduce fatigue. If they’re worn or damaged, they won’t be able to effectively dampen vibration. Inspect the anti-vibration mounts for cracks, tears, or excessive wear. Replace them if necessary. This is a more complex repair, and I recommend taking your chainsaw to a qualified technician.

  • Skill Level: Intermediate to Advanced.
  • Strategic Insight: Replacing worn anti-vibration mounts can significantly improve comfort and reduce fatigue.

Anecdote:

I once experienced severe vibration while cutting a large oak log. I initially thought it was a problem with the engine, but after inspecting the chainsaw, I discovered that the bar was loose. Tightening the bar nuts eliminated the vibration immediately. This taught me the importance of regularly checking all the components of my chainsaw.

Next Steps and Implementation Guidance:

Now that you’re armed with these troubleshooting tips, I encourage you to put them into practice. Start by familiarizing yourself with the components of your Stihl MS170. Regularly inspect your chainsaw for signs of wear or damage. Perform routine maintenance, such as cleaning the air filter, replacing the fuel filter, and sharpening the chain. And most importantly, always prioritize safety when operating your chainsaw. Wear appropriate safety gear, including eye protection, hearing protection, gloves, and chaps.

Remember, preventative maintenance is key to keeping your Stihl MS170 running smoothly for years to come. By following these tips and taking good care of your chainsaw, you’ll be able to tackle any wood processing or firewood preparation project with confidence. And if you ever encounter a problem you can’t solve yourself, don’t hesitate to seek the help of a qualified technician. Happy cutting!

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