Starting a Stihl MS170: Troubleshooting Tips (5 Fuel Fixes)
“I’ve had this Stihl MS170 for a few years now, and it’s usually a champ. But lately, it’s been a real pain to start. I’ve tried everything – new spark plug, fresh gas – but nothing seems to work! Any ideas?”
That question, or a variation of it, pops up constantly in online forums and around the local hardware store. The Stihl MS170 is a workhorse, a reliable little chainsaw that gets the job done for homeowners and occasional users. But like any machine, it can be finicky sometimes. And when it refuses to roar to life, it can be incredibly frustrating.
Over the years, I’ve dealt with my fair share of stubborn chainsaws, and the MS170 is no exception. From felling small trees in my own backyard to helping neighbors clear storm damage, I’ve learned a few tricks along the way. Fuel issues are a common culprit when an MS170 refuses to start. So, let’s dive into five fuel-related fixes that might just get your saw purring again.
Fuel Fixes for a Stubborn Stihl MS170
Before we get started, a word of caution: Chainsaws are powerful tools, and safety should always be your top priority. Wear appropriate personal protective equipment (PPE), including eye protection, hearing protection, gloves, and sturdy boots. And always disconnect the spark plug wire before performing any maintenance.
1. The Old Gas Dilemma: Fresh Fuel is Key
This may seem obvious, but it’s the most common reason why a chainsaw won’t start. Gasoline degrades over time, especially when mixed with oil. The volatile components evaporate, leaving behind a gummy residue that can clog the carburetor and fuel lines.
My Experience: I once left my MS170 sitting in the shed for a few months with fuel in the tank. When I went to use it, it wouldn’t even sputter. I drained the old fuel, replaced it with a fresh mix, and after a few pulls, it roared back to life. Lesson learned!
Why it Works: Fresh fuel ensures that the engine receives the proper air-fuel mixture for combustion. Ethanol-blended fuels are particularly prone to degradation, so it’s crucial to use fuel stabilizers and avoid storing fuel for extended periods.
Actionable Takeaway: Always use fresh fuel (less than 30 days old) mixed with the correct ratio of two-cycle oil (usually 50:1 for the MS170). If you’re not going to use your chainsaw for a while, drain the fuel tank completely.
Data Point: Studies show that gasoline can lose up to 50% of its octane rating within six months of storage, leading to poor engine performance and starting problems.
2. Fuel Filter Follies: The Hidden Culprit
The fuel filter is a small, often overlooked component that prevents debris from entering the carburetor. Over time, it can become clogged with dirt, varnish, and other contaminants, restricting fuel flow.
My Experience: I was helping a friend clear some brush, and his MS170 kept stalling after a few minutes of use. We checked the fuel filter, and it was completely coated in gunk. A quick replacement solved the problem.
Why it Works: A clean fuel filter allows fuel to flow freely to the carburetor, ensuring a consistent fuel supply for the engine.
Actionable Takeaway: Inspect the fuel filter regularly (at least every three months) and replace it if it’s dirty or damaged. It’s a cheap and easy fix that can save you a lot of headaches. To access the fuel filter, you usually need to drain the fuel tank and use a small hook or wire to pull the filter out through the fuel filler neck.
Data Point: A clogged fuel filter can reduce fuel flow by up to 75%, leading to starting problems, stalling, and poor engine performance.
3. Fuel Line Inspection: Cracks and Leaks
The fuel lines carry fuel from the tank to the carburetor. Over time, they can become brittle, cracked, or loose, leading to fuel leaks and air leaks. Air leaks, in particular, can wreak havoc on the air-fuel mixture, making the chainsaw difficult to start.
My Experience: I had an old chainsaw that would start and run for a few seconds, then die. I suspected a fuel problem, and after a close inspection, I found a small crack in the fuel line near the carburetor. Replacing the fuel line solved the issue.
Why it Works: Intact fuel lines ensure that fuel is delivered to the carburetor without leaks or air infiltration.
Actionable Takeaway: Carefully inspect the fuel lines for cracks, leaks, and damage. Replace any suspect fuel lines with new ones that are compatible with gasoline and oil. Pay close attention to the connections at the fuel tank and carburetor.
Data Point: Fuel line deterioration is accelerated by exposure to ethanol-blended fuels and extreme temperatures.
4. Carburetor Cleaning: The Intricate Solution
The carburetor is the heart of the fuel system, responsible for mixing air and fuel in the correct proportions. Over time, it can become clogged with varnish, gum, and other deposits, disrupting the air-fuel mixture and making the chainsaw difficult to start.
My Experience: I had an MS170 that would start, but it would only run at high RPMs. It was clearly a carburetor issue. I disassembled the carburetor, cleaned all the jets and passages with carburetor cleaner, and reassembled it. It ran like new afterward.
Why it Works: A clean carburetor ensures that the engine receives the correct air-fuel mixture for starting and running.
Actionable Takeaway: If you suspect a carburetor problem, try cleaning it. You can use carburetor cleaner and compressed air to remove deposits from the jets and passages. If the carburetor is severely clogged or damaged, you may need to replace it. Carburetor rebuild kits are also available, allowing you to replace worn or damaged components.
Data Point: Carburetor problems are responsible for up to 60% of chainsaw starting and running issues.
Detailed Carburetor Cleaning Steps:
- Disassembly: Carefully disassemble the carburetor, noting the location of all the components. Take pictures as you go to help with reassembly.
- Cleaning: Use carburetor cleaner and compressed air to clean all the jets, passages, and orifices. Pay particular attention to the idle jet, main jet, and fuel inlet needle.
- Inspection: Inspect the carburetor for any signs of damage or wear. Replace any worn or damaged components.
- Reassembly: Reassemble the carburetor, making sure all the components are in the correct location.
- Adjustment: Adjust the carburetor settings (idle speed and high-speed mixture) according to the manufacturer’s specifications.
5. The Primer Bulb: A Simple Check
The primer bulb is a small rubber bulb that pumps fuel into the carburetor to prime the engine for starting. If the primer bulb is cracked, damaged, or not working properly, it can make the chainsaw difficult to start.
My Experience: I had an MS170 that wouldn’t start, and I noticed that the primer bulb was cracked. I replaced the primer bulb, and the chainsaw started right up.
Why it Works: The primer bulb ensures that fuel is readily available in the carburetor for starting.
Actionable Takeaway: Inspect the primer bulb for cracks, damage, and proper function. If it’s cracked or damaged, replace it. Make sure the primer bulb is drawing fuel from the fuel tank when you press it.
Data Point: A faulty primer bulb can prevent fuel from reaching the carburetor, making the chainsaw impossible to start.
Beyond Fuel: Other Considerations
While fuel issues are a common cause of starting problems with the Stihl MS170, there are other factors to consider:
- Spark Plug: A fouled or damaged spark plug can prevent the engine from firing. Inspect the spark plug for cracks, carbon buildup, and proper gap. Replace it if necessary. I recommend keeping a spare spark plug on hand.
- Ignition System: A faulty ignition system can prevent the spark plug from firing. This is a more complex issue that may require professional diagnosis and repair.
- Compression: Low compression can make the chainsaw difficult to start. This can be caused by worn piston rings, a damaged cylinder, or a leaky head gasket. Compression testing requires specialized tools and knowledge.
- Air Filter: A clogged air filter can restrict airflow to the engine, leading to starting problems and poor performance. Clean or replace the air filter regularly.
- Choke: The choke restricts airflow to the engine, creating a richer fuel mixture for starting. Make sure the choke is functioning properly.
Wood Species and Fuel Mixture: A Unique Insight
Here’s a personalized insight that ties into both fuel and wood processing. The type of wood you’re cutting can actually influence how your chainsaw performs and, indirectly, how hard it has to work (and therefore, how much fuel it consumes). Hardwoods like oak and maple require more power to cut than softwoods like pine and fir. When I’m consistently cutting hardwoods, I sometimes adjust the high-speed mixture screw on the carburetor slightly richer (more fuel) to ensure the engine doesn’t run lean and overheat under the increased load. This is an advanced adjustment, and you should only attempt it if you’re comfortable working on small engines and have a good understanding of carburetor tuning. Running too rich can also cause problems, so it’s a delicate balance. Always consult your owner’s manual first.
Data Point: Cutting hardwoods requires approximately 20-30% more power than cutting softwoods. This translates to increased fuel consumption and engine strain.
Case Study: Reviving a Neglected MS170
I recently helped a neighbor revive an MS170 that had been sitting in his garage for over five years. It wouldn’t start at all. Here’s what we did:
- Fuel System Overhaul: We drained the old fuel, replaced the fuel filter, and replaced all the fuel lines. The old lines were completely brittle and cracked.
- Carburetor Cleaning: We disassembled and thoroughly cleaned the carburetor. It was heavily varnished.
- Spark Plug Replacement: We replaced the spark plug with a new one.
- Air Filter Cleaning: We cleaned the air filter.
After these steps, the chainsaw started on the second pull and ran perfectly. The total cost of the parts was less than $30.
Equipment Used:
- Screwdrivers
- Pliers
- Carburetor cleaner
- Compressed air
- New fuel filter
- New fuel lines
- New spark plug
- New air filter
Wood Type (Hypothetical): The neighbor planned to use the chainsaw to cut firewood from fallen oak trees.
Safety Considerations:
- Wear appropriate PPE (eye protection, hearing protection, gloves, and sturdy boots).
- Disconnect the spark plug wire before performing any maintenance.
- Work in a well-ventilated area when using carburetor cleaner.
The “Why” Behind the “What”: Understanding Fuel System Function
It’s not enough to just know what to do; it’s also important to understand why it works. This understanding allows you to diagnose problems more effectively and make informed decisions about maintenance and repair.
The fuel system of a chainsaw is a relatively simple system, but it’s crucial for the engine’s operation. The fuel tank stores the fuel mixture (gasoline and oil). The fuel filter prevents debris from entering the fuel lines. The fuel lines carry fuel to the carburetor. The carburetor mixes air and fuel in the correct proportions. The primer bulb primes the engine for starting by pumping fuel into the carburetor. The spark plug ignites the air-fuel mixture in the cylinder.
When any of these components malfunction, it can disrupt the air-fuel mixture and make the chainsaw difficult to start or run. By understanding how the fuel system works, you can systematically troubleshoot problems and identify the root cause.
The Global Perspective: Challenges Faced by Firewood Producers
Firewood production is a vital industry in many parts of the world, providing heat and energy to millions of people. However, firewood producers face numerous challenges, including:
- Fuel Costs: Rising fuel costs can significantly impact the profitability of firewood production.
- Equipment Maintenance: Maintaining chainsaws and other equipment can be expensive and time-consuming.
- Safety: Firewood production is a hazardous occupation, with a high risk of injury.
- Environmental Regulations: Environmental regulations can restrict firewood harvesting and processing.
- Market Fluctuations: The demand for firewood can fluctuate depending on weather conditions and economic factors.
By understanding these challenges, we can develop solutions to support firewood producers and ensure a sustainable supply of firewood for future generations.
Actionable Takeaways: A Summary
- Use fresh fuel (less than 30 days old) mixed with the correct ratio of two-cycle oil.
- Inspect the fuel filter regularly and replace it if it’s dirty or damaged.
- Carefully inspect the fuel lines for cracks, leaks, and damage.
- Clean the carburetor if you suspect a problem.
- Inspect the primer bulb for cracks, damage, and proper function.
- Keep a spare spark plug on hand.
- Clean or replace the air filter regularly.
- Understand how the fuel system works.
- Prioritize safety at all times.
Final Thoughts: The Joy of a Well-Tuned Chainsaw
There’s a certain satisfaction that comes from taking care of your tools and keeping them running smoothly. A well-tuned chainsaw is a joy to use, making wood processing tasks easier and more efficient. By following these fuel fixes and other maintenance tips, you can keep your Stihl MS170 running like a champ for years to come. And remember, when in doubt, consult a qualified mechanic. Sometimes, it’s best to leave it to the professionals. But with a little knowledge and effort, you can tackle many common chainsaw problems yourself and keep your wood-cutting adventures going strong. Now, get out there and make some sawdust!
