MS170 Chainsaw Troubleshooting Tips (5 Pro Arborist Hacks)

Did you know that approximately 40% of chainsaw-related injuries are preventable with proper maintenance and troubleshooting? As a seasoned arborist with over 20 years under my belt, I’ve seen my fair share of MS170 chainsaws sputtering and stalling. The Stihl MS170 is a workhorse, a reliable entry-level saw that’s perfect for homeowners tackling small to medium-sized tasks. But like any machine, it has its quirks. In this guide, I’ll share some pro arborist hacks to keep your MS170 running smoothly. I’ll walk you through common problems and how to fix them.

MS170 Chainsaw Troubleshooting: Pro Arborist Hacks

The MS170 is designed for pruning, light felling, and preparing firewood. It’s not meant for heavy, prolonged use. Overworking it is a common mistake I see. This guide covers key areas: fuel issues, ignition problems, carburetor adjustments, lubrication challenges, and preventative maintenance.

1. Fuel System Troubleshooting: The Lifeblood of Your Saw

A clean and properly mixed fuel supply is essential for optimal performance. Fuel-related issues are the most common culprits behind a balky MS170.

Understanding Fuel Mix Ratios

The MS170, like most two-stroke engines, requires a precise mix of gasoline and oil. Stihl recommends a 50:1 ratio. This means 50 parts gasoline to 1 part two-stroke oil. Using the wrong ratio can lead to serious engine damage. Too little oil causes excessive wear, while too much can foul the spark plug and create excessive carbon buildup.

• The Right Stuff: I always recommend using a high-quality, name-brand two-stroke oil specifically designed for air-cooled engines. Stihl Ultra HP is my go-to, but other reputable brands like Husqvarna and Echo work well too.
• Mixing Matters: I use a dedicated fuel mixing container with clear markings for both gasoline and oil. This ensures accuracy. Never eyeball it! A slight inaccuracy can cause problems down the line.
• Fresh is Best: Gasoline degrades over time, especially when mixed with oil. I never use fuel that’s been sitting for more than 30 days. Stale fuel can clog the carburetor and make starting difficult. I always tell people to mark the date on the fuel can when they mix it.
• Ethanol Concerns: Ethanol-blended gasoline can cause problems in small engines. Ethanol attracts water, which can lead to corrosion and fuel separation. If possible, use ethanol-free gasoline. If not, add a fuel stabilizer to help prevent problems. I’ve seen countless carburetors ruined by ethanol damage.

Actionable Metric: Aim for a fuel mixture within +/- 2% of the recommended 50:1 ratio for optimal engine health.

Diagnosing Fuel Delivery Problems

If your MS170 is hard to start, stalls frequently, or lacks power, the fuel system is a prime suspect.

• Fuel Filter Inspection: The fuel filter is located inside the fuel tank, attached to the end of the fuel line. To check it, carefully remove the fuel cap and use a clean piece of wire to hook the filter and pull it out. If the filter is dirty or clogged, replace it. I usually replace mine every six months, or sooner if I’m using the saw frequently.
• Fuel Line Integrity: Inspect the fuel line for cracks, leaks, or kinks. A damaged fuel line can allow air to enter the system, disrupting fuel flow. I recommend replacing the fuel line every year or two, as they tend to dry out and crack over time.
• Carburetor Cleaning: The carburetor is a complex component that mixes air and fuel. Over time, it can become clogged with varnish and debris. If the fuel filter and lines are clear, the carburetor may need cleaning. I use a carburetor cleaner spray and compressed air to clean the carburetor jets and passages. For a deep clean, you might consider disassembling the carburetor, but this requires some mechanical skill.
• Primer Bulb Check: The primer bulb helps draw fuel into the carburetor. If the bulb is cracked or damaged, it won’t work properly. Check the bulb for leaks and replace it if necessary. I’ve seen primer bulbs crack simply from age and exposure to the sun.

Case Study: A customer brought in an MS170 that wouldn’t start. After checking the fuel filter and lines, I discovered that the carburetor was completely clogged with varnish from old fuel. A thorough cleaning of the carburetor restored the saw to perfect working order.

Takeaway: Regularly inspect and maintain your fuel system to prevent costly repairs. Fresh fuel, a clean filter, and intact fuel lines are essential for reliable performance.

2. Ignition System Troubleshooting: Sparking the Power

The ignition system is responsible for creating the spark that ignites the fuel-air mixture. A weak or nonexistent spark will prevent the engine from starting.

Spark Plug Inspection and Testing

The spark plug is a critical component of the ignition system. It should be inspected regularly for wear and fouling.

• Visual Inspection: Remove the spark plug and examine it. A healthy spark plug will have a clean, light brown insulator. A black, oily spark plug indicates excessive oil in the fuel mixture or worn piston rings. A white, chalky spark plug indicates a lean fuel mixture.
• Spark Plug Gap: The gap between the center electrode and the side electrode is crucial for proper ignition. The correct gap for the MS170 is typically 0.5mm (0.020 inches). Use a spark plug gap tool to adjust the gap if necessary. I always double-check the gap with a feeler gauge.
• Spark Test: To test the spark plug, reattach it to the spark plug wire and ground the side electrode against the engine cylinder. Pull the starter rope. You should see a strong, blue spark jumping across the gap. A weak, yellow spark or no spark at all indicates a problem with the ignition system.
• Spark Plug Replacement: I recommend replacing the spark plug every year, or sooner if it shows signs of wear or fouling. A fresh spark plug can make a big difference in starting and performance.

Actionable Metric: Aim for a consistent, strong blue spark when testing the spark plug.

Diagnosing Ignition Coil Problems

The ignition coil generates the high-voltage electricity needed to create the spark. If the spark plug is good but you’re still not getting a spark, the ignition coil may be faulty.

• Coil Air Gap: The ignition coil must be properly positioned in relation to the flywheel. The air gap between the coil and the flywheel should be approximately 0.3mm (0.012 inches). Use a business card or feeler gauge to set the air gap. I’ve seen cases where the coil was too far away, resulting in a weak spark.
• Coil Testing: Testing the ignition coil requires a multimeter. Disconnect the spark plug wire from the coil and set the multimeter to measure resistance. Connect the multimeter leads to the coil terminals. A faulty coil will have an open circuit or an incorrect resistance reading.
• Coil Replacement: Replacing the ignition coil is a relatively simple task. Disconnect the old coil, install the new coil, and set the air gap. I always make sure to use the correct replacement coil for the MS170.

Personal Story: I once spent hours troubleshooting an MS170 that wouldn’t start. I replaced the spark plug, cleaned the carburetor, and checked the fuel lines, but nothing worked. Finally, I decided to test the ignition coil, and it turned out to be the culprit. Replacing the coil solved the problem immediately.

Takeaway: A properly functioning ignition system is essential for starting and running your MS170. Regularly inspect the spark plug and consider testing the ignition coil if you suspect a problem.

3. Carburetor Adjustment: Fine-Tuning Performance

The carburetor is responsible for delivering the correct air-fuel mixture to the engine. Improper carburetor adjustment can lead to poor performance, stalling, and excessive fuel consumption.

Understanding Carburetor Settings

The MS170 carburetor typically has two adjustment screws: the “H” screw (high-speed) and the “L” screw (low-speed). Adjusting these screws affects the air-fuel mixture at different engine speeds.

• “H” Screw (High-Speed): This screw controls the fuel mixture at high engine speeds. Turning the “H” screw clockwise leans the mixture (less fuel), while turning it counterclockwise richens the mixture (more fuel).
• “L” Screw (Low-Speed): This screw controls the fuel mixture at idle and low engine speeds. Turning the “L” screw clockwise leans the mixture, while turning it counterclockwise richens the mixture.
• Idle Speed Screw: This screw controls the engine idle speed. Turning it clockwise increases the idle speed, while turning it counterclockwise decreases the idle speed.

Important Note: Carburetor adjustment should be done with the engine warm and running.

Basic Carburetor Adjustment Procedure

The following is a basic procedure for adjusting the carburetor on an MS170.

1. Warm Up the Engine: Start the engine and let it warm up for a few minutes.
2. Locate the Adjustment Screws: The “H” and “L” screws are typically located on the side of the carburetor.
3. Initial Settings: Turn both the “H” and “L” screws clockwise until they are lightly seated. Then, back them out 1 to 1.5 turns. This is a good starting point.
4. Adjust the “L” Screw: With the engine running, slowly turn the “L” screw clockwise or counterclockwise until the engine idles smoothly. If the engine stalls, turn the “L” screw counterclockwise slightly.
5. Adjust the Idle Speed Screw: Adjust the idle speed screw until the chain stops moving when the engine is idling.
6. Adjust the “H” Screw: With the engine running at full throttle, slowly turn the “H” screw clockwise or counterclockwise until the engine runs smoothly and doesn’t bog down.
7. Fine-Tuning: After making these adjustments, let the engine cool down and then restart it to see how it performs. You may need to make further adjustments to achieve optimal performance.

Pro Tip: Listen to the engine carefully while making adjustments. A lean mixture will cause the engine to run hot and sound “tinny.” A rich mixture will cause the engine to smoke and bog down.

Actionable Metric: Aim for a smooth idle, responsive throttle, and no bogging or stalling at high speeds.

Troubleshooting Carburetor Adjustment Issues

If you’re having trouble adjusting the carburetor, consider the following:

• Clogged Carburetor: A clogged carburetor can prevent proper adjustment. Clean the carburetor thoroughly before attempting to adjust it.
• Air Leaks: Air leaks in the intake system can disrupt the air-fuel mixture. Check the intake manifold and carburetor mounting bolts for leaks.
• Worn Carburetor Components: Worn carburetor components, such as the needle valve and seat, can affect adjustment. Consider rebuilding the carburetor if it’s old or worn.

Case Study: I had a customer who complained that his MS170 was constantly stalling. After checking the fuel system and ignition system, I determined that the carburetor was the problem. The “L” screw was completely closed, preventing the engine from getting enough fuel at idle. After adjusting the “L” screw, the saw ran perfectly.

Takeaway: Proper carburetor adjustment is essential for optimal performance. Take the time to learn how to adjust the carburetor on your MS170, and you’ll be rewarded with a saw that runs smoothly and reliably.

4. Lubrication System Troubleshooting: Keeping it Oiled

Proper lubrication is crucial for extending the life of your chainsaw. The MS170 has an automatic oiler that lubricates the chain and bar. Problems with the lubrication system can lead to premature wear and damage.

Checking the Oiler Output

The first step in troubleshooting lubrication problems is to check the oiler output.

• Visual Inspection: Start the engine and hold the saw over a piece of cardboard or wood. You should see a steady stream of oil being ejected from the chain. If you don’t see any oil, or if the oil flow is weak, there may be a problem with the oiler.
• Adjusting the Oiler: Some MS170 models have an adjustable oiler. If your saw has this feature, try adjusting the oiler to increase the oil flow.
• Checking the Oil Tank: Make sure the oil tank is full. A low oil level can prevent the oiler from working properly.

Actionable Metric: Aim for a consistent stream of oil being ejected from the chain when the engine is running.

Diagnosing Oiler Problems

If the oiler is not working properly, there are several potential causes.

• Clogged Oiler: The oiler can become clogged with debris, preventing oil from flowing properly. Clean the oiler with compressed air or a small wire. I use a pipe cleaner to clear out any blockages.
• Clogged Oil Filter: The oil tank has a filter that prevents debris from entering the oiler. If the filter is clogged, it can restrict oil flow. Clean or replace the oil filter.
• Damaged Oiler Pump: The oiler pump is responsible for pumping oil to the chain. If the pump is damaged, it may not be able to generate enough pressure to lubricate the chain. Replace the oiler pump.
• Blocked Oil Passage: The oil passage that carries oil from the oiler to the bar can become blocked. Clean the oil passage with compressed air or a small wire.

Personal Story: I once had an MS170 that was constantly overheating. I discovered that the oiler was completely clogged, preventing the chain from being lubricated. After cleaning the oiler, the saw ran much cooler and the chain lasted longer.

Takeaway: Proper lubrication is essential for extending the life of your chainsaw. Regularly check the oiler output and troubleshoot any problems promptly.

Choosing the Right Bar and Chain Oil

Using the correct bar and chain oil is just as important as maintaining the oiler.

• Viscosity: Choose a bar and chain oil with the correct viscosity for your climate. In colder climates, use a lower viscosity oil to ensure proper flow. In warmer climates, use a higher viscosity oil to prevent it from thinning out too much.
• Tackiness: Choose a bar and chain oil with good tackiness. Tackiness refers to the oil’s ability to cling to the chain and bar. A tacky oil will provide better lubrication and reduce wear.
• Biodegradability: Consider using a biodegradable bar and chain oil. Biodegradable oils are environmentally friendly and can reduce your impact on the environment.

Pro Tip: I always recommend using a bar and chain oil specifically designed for chainsaws. These oils contain additives that help to reduce wear and prevent corrosion.

Actionable Metric: Aim for a bar and chain oil viscosity appropriate for your climate and good tackiness for optimal lubrication.

5. Preventative Maintenance: The Key to Longevity

Preventative maintenance is the key to keeping your MS170 running smoothly for years to come. Regular maintenance can prevent costly repairs and extend the life of your saw.

Regular Cleaning and Inspection

• Air Filter: Clean the air filter regularly. A dirty air filter can restrict airflow and reduce engine performance. I clean mine after every use.
• Cylinder Fins: Keep the cylinder fins clean. The cylinder fins help to dissipate heat. If they are clogged with debris, the engine can overheat.
• Chain Sharpness: Keep the chain sharp. A dull chain will put more strain on the engine and can be dangerous to use. I sharpen my chain every few hours of use.
• Bar Condition: Inspect the bar regularly for wear and damage. A worn or damaged bar can affect chain performance and can be dangerous.
• Tighten Loose Screws: Check all screws and bolts regularly and tighten them if necessary. Loose screws can cause vibrations and damage to the saw.

Actionable Metric: Aim to clean the air filter after each use, sharpen the chain every few hours, and inspect the bar and screws regularly.

Seasonal Maintenance

• Fuel System: At the end of the season, drain the fuel tank and run the engine until it stalls. This will prevent fuel from sitting in the carburetor and causing problems.
• Spark Plug: Remove the spark plug and spray a small amount of oil into the cylinder. This will help to prevent corrosion during storage.
• Storage: Store the saw in a dry place. Cover the saw to protect it from dust and moisture.

Case Study: A customer brought in an MS170 that had been stored improperly for several years. The carburetor was completely clogged with varnish, the fuel lines were cracked, and the spark plug was corroded. It took several hours of work to get the saw running again.

Takeaway: Preventative maintenance is essential for keeping your MS170 running smoothly. Take the time to perform regular maintenance tasks, and you’ll be rewarded with a saw that lasts for years.

Chain Maintenance: Keeping Your Cut Clean

A sharp chain is not only more efficient but also safer. A dull chain requires more force, increasing the risk of kickback.

• Sharpening Techniques: Learn how to sharpen your chain properly. Use a chain sharpening kit with the correct file size and angle. I prefer using a hand file for precise sharpening, but a chain grinder can be faster for more significant damage.
• Depth Gauge Adjustment: Adjust the depth gauges (rakers) after sharpening. The depth gauges control how much wood the chain removes with each cut. If the depth gauges are too high, the chain will cut slowly. If they are too low, the chain will grab and kickback.
• Chain Tension: Maintain proper chain tension. A loose chain can derail and cause damage. A tight chain can overheat and wear prematurely. I check the tension every time I refuel.
• Chain Lubrication: Ensure proper chain lubrication. A properly lubricated chain will cut more efficiently and last longer.

Actionable Metric: Aim for a chain tension that allows slight sag on the bottom of the bar and depth gauges adjusted according to the manufacturer’s specifications.

Pro Tip: Keep a spare chain on hand. This will allow you to quickly replace a dull or damaged chain and keep working.

By following these pro arborist hacks, you can keep your MS170 chainsaw running smoothly and reliably for years to come. Remember to prioritize safety, perform regular maintenance, and address any problems promptly. With a little care and attention, your MS170 will be a valuable tool for all your cutting needs.

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