Stihl MS170 Carb Replacement Tips (3 Pro Fixes for Smoother Cuts)
The hum of a well-tuned chainsaw is music to my ears. It signifies progress, warmth in the winter, and the satisfaction of a job well done. But let’s face it, sometimes that hum turns into a sputter, a cough, or worse – silence. And more often than not, the culprit is the carburetor. In today’s world, where we have drones mapping forests and AI optimizing timber yields, it’s easy to forget the fundamentals. But even with all the tech innovations around us, a simple carburetor issue can bring the whole operation to a standstill. That’s where understanding how to troubleshoot and fix your chainsaw becomes essential.
Globally, the wood processing and firewood industry is a multi-billion dollar sector. Recent statistics indicate a growing demand for sustainably sourced firewood, particularly in Europe and North America, driven by rising energy costs and a renewed interest in traditional heating methods. However, the industry faces challenges such as labor shortages, increasing equipment costs, and stricter environmental regulations. Small workshops and independent loggers are particularly vulnerable, often relying on older equipment like the Stihl MS170, a reliable but sometimes temperamental workhorse.
In this guide, I’ll share my years of experience working with chainsaws, specifically the Stihl MS170, and walk you through three pro-level fixes for carburetor issues that will get your saw cutting smoother than ever. Think of this as your “get-out-of-the-woods” card when your MS170 decides to throw a tantrum.
Stihl MS170 Carb Replacement: 3 Pro Fixes for Smoother Cuts
The Stihl MS170 is a popular choice for homeowners and smaller firewood operations. It’s lightweight, easy to handle, and relatively affordable. But like any piece of machinery, it requires maintenance, and the carburetor is a common point of failure. Before diving in, let’s define some key concepts to ensure everyone is on the same page.
Understanding the Basics: Green Wood vs. Seasoned Wood, and Why Carburetor Tuning Matters
Green Wood: This is freshly cut wood with high moisture content. Cutting green wood puts more strain on your chainsaw because it’s denser and harder to cut through. The higher resistance can lead to overheating and carburetor issues.
Seasoned Wood: This is wood that has been allowed to dry, typically for 6-12 months, reducing its moisture content. Seasoned wood is easier to cut, burns cleaner, and produces more heat.
Why Carburetor Tuning Matters: The carburetor is responsible for mixing air and fuel in the correct ratio for combustion. A properly tuned carburetor ensures efficient fuel consumption, optimal engine performance, and reduced emissions. When cutting different types of wood, or when environmental conditions change (temperature, altitude), you might need to adjust the carburetor to maintain peak performance.
Signs of a Carburetor Problem
Before you start tearing things apart, it’s crucial to identify if the carburetor is indeed the problem. Here are some common symptoms:
- Difficulty Starting: The saw cranks but won’t start, or it takes multiple attempts to get it running.
- Rough Idling: The engine idles erratically, stalls frequently, or runs at a very low RPM.
- Poor Acceleration: The saw hesitates or bogs down when you try to accelerate.
- Loss of Power: The saw lacks its usual cutting power, especially when cutting thicker wood.
- Excessive Smoke: The engine produces excessive smoke, which can indicate an overly rich fuel mixture.
If you’re experiencing any of these symptoms, it’s time to investigate the carburetor.
Pro Fix #1: The Thorough Carburetor Cleaning
This is often the first and most effective solution. Over time, fuel residue, dirt, and varnish can build up inside the carburetor, restricting fuel flow and affecting performance.
Tools and Materials You’ll Need
- Screwdrivers: A set of flathead and Phillips head screwdrivers.
- Carburetor Cleaner: A high-quality carburetor cleaner spray. I recommend using a brand specifically designed for small engines.
- Compressed Air: A can of compressed air or an air compressor with a nozzle.
- Small Brushes: A set of small brushes, like old toothbrushes or carburetor cleaning brushes.
- Needle-Nose Pliers: For removing small parts.
- Clean Rags: For wiping down parts.
- Safety Glasses: Protect your eyes from carburetor cleaner spray.
- Gloves: Protect your hands from chemicals.
- Camera or Phone: To take pictures of the carburetor before disassembly. This will help you remember how everything goes back together.
- Parts Diagram: A diagram of the Stihl MS170 carburetor. You can usually find this online or in the saw’s manual.
Step-by-Step Cleaning Process
- Safety First: Disconnect the spark plug wire to prevent accidental starting. Ensure the chainsaw is cool before you begin.
- Remove the Air Filter: Locate the air filter cover, usually on top of the engine. Remove the cover and take out the air filter. Inspect the air filter and clean or replace it if necessary. A clogged air filter can also cause carburetor problems.
- Remove the Carburetor Cover: Carefully remove any covers or shields that are blocking access to the carburetor.
- Disconnect Fuel Lines and Linkages: Gently disconnect the fuel lines from the carburetor. Use needle-nose pliers if necessary. Be careful not to damage the fuel lines. Also, disconnect any throttle linkages or choke linkages.
- Remove the Carburetor: Unscrew the bolts or screws that hold the carburetor to the engine. Carefully remove the carburetor.
- Disassemble the Carburetor: This is where the photos and diagram become crucial. Carefully disassemble the carburetor, noting the location of each part. Remove the fuel bowl, needle valve, jets, and any other removable components.
- Clean the Parts: Spray all the carburetor parts with carburetor cleaner. Use the small brushes to scrub away any dirt or varnish. Pay special attention to the jets, as these are easily clogged.
- Clean the Carburetor Body: Spray the carburetor body with carburetor cleaner and use the brushes to clean out any passages or orifices.
- Blow Out Passages with Compressed Air: Use compressed air to blow out all the passages in the carburetor body and the individual parts. This will ensure that all the cleaner and debris are removed.
- Inspect the Parts: Carefully inspect all the parts for wear or damage. Replace any parts that are worn or damaged. Common parts to replace are the needle valve, gaskets, and diaphragms.
- Reassemble the Carburetor: Reassemble the carburetor in the reverse order of disassembly, using your photos and diagram as a guide. Make sure all the parts are properly seated and tightened.
- Reinstall the Carburetor: Reinstall the carburetor onto the engine, connecting the fuel lines and linkages.
- Reinstall the Air Filter and Cover: Reinstall the air filter and cover.
- Reconnect the Spark Plug Wire: Reconnect the spark plug wire.
- Test the Saw: Start the saw and let it idle for a few minutes. Listen for any unusual noises or vibrations. Adjust the carburetor if necessary (see Pro Fix #2).
Real-World Example
I once had a Stihl MS170 that was running terribly. It would start, but it would stall as soon as I gave it any throttle. I tried adjusting the carburetor screws, but nothing seemed to work. Finally, I decided to take the carburetor apart and clean it. I was amazed at how much gunk was inside. After cleaning everything thoroughly and reassembling the carburetor, the saw ran like new. It was a simple fix, but it made a world of difference.
Data Point
In a study conducted by a small engine repair shop, it was found that 70% of carburetor problems in Stihl MS170 chainsaws could be resolved with a thorough cleaning.
Pro Fix #2: Carburetor Adjustment: The Fine-Tuning Art
Even after cleaning, your carburetor might need adjustment. This involves tweaking the high (H) and low (L) speed screws to optimize the fuel/air mixture.
Understanding Carburetor Adjustment Screws
- L (Low Speed Screw): Controls the fuel/air mixture at idle and low speeds.
- H (High Speed Screw): Controls the fuel/air mixture at high speeds.
- LA (Idle Speed Screw): Controls the engine’s idle speed.
Tools You’ll Need
- Screwdriver: A small flathead screwdriver that fits the carburetor adjustment screws.
- Tachometer (Optional): A tachometer can help you accurately set the idle speed.
Adjustment Procedure
- Locate the Adjustment Screws: The adjustment screws are usually located on the side of the carburetor. Refer to your saw’s manual or a parts diagram to identify the L, H, and LA screws.
- Warm Up the Engine: Start the saw and let it warm up for a few minutes.
- Adjust the Idle Speed (LA): Turn the LA screw clockwise to increase the idle speed and counterclockwise to decrease it. Adjust the idle speed until the engine runs smoothly without stalling. The ideal idle speed for the Stihl MS170 is around 2,800-3,200 RPM.
- Adjust the Low Speed (L): Turn the L screw slowly clockwise until the engine starts to stumble or stall. Then, turn it counterclockwise until the engine runs smoothly and accelerates without hesitation.
- Adjust the High Speed (H): This is the trickiest part. You need to listen to the engine carefully. Run the saw at full throttle and listen for any signs of a lean or rich condition.
- Lean Condition (Too Little Fuel): The engine will sound high-pitched and may surge or cut out. Turn the H screw counterclockwise to richen the mixture.
- Rich Condition (Too Much Fuel): The engine will sound sluggish and produce excessive smoke. Turn the H screw clockwise to lean out the mixture.
- Optimal Setting: The engine should run smoothly at full throttle without any hesitation or surging.
- Fine-Tune the Adjustments: After making the initial adjustments, go back and fine-tune the L and H screws until you achieve the best possible performance.
- Test the Saw: Cut some wood to test the saw’s performance under load. Make any final adjustments as needed.
Important Considerations
- Altitude: At higher altitudes, the air is thinner, which means you need to lean out the fuel mixture. Turn the H and L screws slightly clockwise.
- Temperature: In cold weather, the air is denser, which means you need to richen the fuel mixture. Turn the H and L screws slightly counterclockwise.
- Listen to Your Engine: The best way to adjust a carburetor is to listen to the engine and make adjustments based on how it sounds.
- Small Adjustments: Make small adjustments and test the saw after each adjustment. It’s better to make several small adjustments than one large adjustment.
My Personal Experience
I remember one time I was helping a friend cut firewood in the mountains. His chainsaw was running poorly, and he couldn’t figure out why. I quickly realized that the carburetor needed adjustment due to the higher altitude. After making a few small adjustments, the saw was running perfectly, and we were able to get the job done quickly and efficiently.
Data Point
According to a survey of chainsaw mechanics, proper carburetor adjustment can improve fuel efficiency by up to 15% and increase cutting power by up to 10%.
Pro Fix #3: The Carburetor Replacement: When All Else Fails
Sometimes, cleaning and adjusting just won’t cut it. If the carburetor is severely damaged or worn, replacement is the only option.
When to Replace the Carburetor
- Cracked or Damaged Body: If the carburetor body is cracked or damaged, it will leak air and fuel, making it impossible to tune properly.
- Worn Internal Parts: If the internal parts, such as the needle valve or jets, are worn beyond repair, the carburetor will not function correctly.
- Unresolvable Tuning Issues: If you’ve tried cleaning and adjusting the carburetor, but you still can’t get the saw to run properly, it’s likely that the carburetor needs to be replaced.
Choosing the Right Replacement Carburetor
- OEM vs. Aftermarket: You have two options: an original equipment manufacturer (OEM) carburetor or an aftermarket carburetor. OEM carburetors are made by the same manufacturer as the original carburetor and are guaranteed to fit and function correctly. Aftermarket carburetors are made by third-party manufacturers and are often less expensive than OEM carburetors. However, the quality and reliability of aftermarket carburetors can vary.
- Compatibility: Make sure the replacement carburetor is compatible with your Stihl MS170. Check the part number and specifications to ensure a proper fit.
- Reputation: Choose a reputable brand of aftermarket carburetor. Read reviews and ask for recommendations from other chainsaw users.
Replacement Procedure
- Safety First: Disconnect the spark plug wire to prevent accidental starting. Ensure the chainsaw is cool before you begin.
- Remove the Old Carburetor: Follow the same steps as in Pro Fix #1 to remove the old carburetor.
- Install the New Carburetor: Install the new carburetor in the reverse order of removal. Make sure all the fuel lines and linkages are properly connected.
- Adjust the Carburetor: Adjust the carburetor according to the procedure in Pro Fix #2.
- Test the Saw: Start the saw and let it idle for a few minutes. Listen for any unusual noises or vibrations. Cut some wood to test the saw’s performance under load. Make any final adjustments as needed.
Cost Considerations
A replacement carburetor for a Stihl MS170 can range in price from $20 for an aftermarket option to $80 or more for an OEM part. Consider the long-term reliability and performance when making your decision. Sometimes, spending a bit more upfront can save you headaches down the road.
Case Study: The Resurrected MS170
I once bought a used Stihl MS170 at a flea market for next to nothing. The saw was in rough shape, and the owner said it wouldn’t run. I took it home and discovered that the carburetor was completely shot. The body was cracked, and the internal parts were corroded. I decided to replace the carburetor with an aftermarket unit. After installing the new carburetor and making a few adjustments, the saw fired right up and ran like a champ. I ended up using that saw for years, and it became one of my favorites. It just goes to show that even a seemingly dead chainsaw can be brought back to life with a little bit of work and a new carburetor.
Data Point
A survey of chainsaw repair shops showed that replacing a carburetor is a cost-effective repair in about 80% of cases where the carburetor is the primary source of the problem, extending the life of the chainsaw significantly.
Additional Tips and Best Practices
- Use Fresh Fuel: Always use fresh, high-quality fuel with the correct oil mixture. Old or contaminated fuel can cause carburetor problems. I recommend using a fuel stabilizer to prevent fuel from going bad.
- Clean the Air Filter Regularly: A clogged air filter can restrict airflow and cause the engine to run rich, leading to carburetor problems. Clean the air filter regularly with soap and water or compressed air.
- Store the Saw Properly: When storing the saw for extended periods, drain the fuel tank and run the engine until it stalls. This will prevent fuel from gumming up the carburetor.
- Regular Maintenance: Regular maintenance, such as cleaning the spark plug and checking the fuel lines, can help prevent carburetor problems.
- Consider a Fuel Filter: Adding an inline fuel filter can help prevent debris from entering the carburetor.
- Ethanol-Free Fuel: If possible, use ethanol-free fuel. Ethanol can damage rubber and plastic parts in the carburetor.
Troubleshooting Common Carburetor Problems
- Saw Won’t Start: Check the spark plug, fuel lines, and air filter. Clean or replace the carburetor if necessary.
- Saw Runs Rough: Adjust the carburetor screws. Clean or replace the carburetor if necessary.
- Saw Stalls Frequently: Adjust the idle speed screw. Clean or replace the carburetor if necessary.
- Saw Lacks Power: Adjust the high-speed screw. Clean or replace the carburetor if necessary.
- Excessive Smoke: Adjust the high-speed screw. Check the fuel mixture.
- Fuel Leaks: Check the fuel lines and carburetor gaskets. Replace any damaged parts.
Costs, Budgeting, and Resource Management
- Carburetor Cleaner: $5-$10
- Replacement Carburetor (Aftermarket): $20-$40
- Replacement Carburetor (OEM): $60-$100
- Fuel Filter: $5-$10
- Air Filter: $5-$10
- Spark Plug: $5-$10
- Labor (If Hiring a Mechanic): $50-$100 per hour
When budgeting for chainsaw maintenance, it’s important to factor in the cost of regular maintenance items like fuel, oil, air filters, and spark plugs. It’s also wise to set aside a small amount of money for unexpected repairs, such as carburetor replacements.
Next Steps and Additional Resources
Now that you’re armed with these pro-level fixes, you can confidently tackle most Stihl MS170 carburetor issues. But remember, safety is paramount. Always wear appropriate safety gear and follow the manufacturer’s instructions.
Here are some additional resources that you might find helpful:
- Stihl Website: The official Stihl website has a wealth of information about their products, including manuals, parts diagrams, and troubleshooting guides.
- Small Engine Repair Forums: Online forums dedicated to small engine repair can be a great source of information and advice.
- Local Chainsaw Repair Shops: If you’re not comfortable working on your chainsaw yourself, take it to a local repair shop.
- YouTube Tutorials: There are many YouTube videos that demonstrate how to clean, adjust, and replace carburetors on Stihl chainsaws.
Suppliers of Logging Tools:
- Bailey’s: A well-known supplier of logging tools and equipment.
- Northern Tool + Equipment: Offers a wide range of tools and equipment for various industries, including logging.
- Forestry Suppliers, Inc.: Specializes in forestry and logging equipment.
Drying Equipment Rental Services:
- Sunbelt Rentals: A large equipment rental company with locations across the country.
- United Rentals: Another major equipment rental company with a wide selection of equipment.
- Local Rental Shops: Check with local rental shops for smaller drying equipment rentals.
Final Thoughts
Fixing a Stihl MS170 carburetor might seem daunting at first, but with a little patience and the right knowledge, it’s a task you can definitely handle. Remember, a well-maintained chainsaw is not just a tool; it’s an investment in your productivity and safety. So, keep your saw sharp, your fuel fresh, and your carburetor clean, and you’ll be cutting wood like a pro in no time. And who knows, maybe you’ll even find yourself enjoying the satisfying hum of a perfectly tuned engine as much as I do!
