Stihl Chainsaw Will Not Stay Running (5 Quick Fixes Every Arborist Uses)

Let’s face it, there’s nothing more frustrating than wrestling with a chainsaw that just won’t cooperate. You pull the cord, it sputters to life, maybe even roars for a few glorious seconds, and then… silence. A dead chainsaw is a productivity killer, and when you’re on a deadline, whether it’s prepping firewood for winter or clearing storm damage, you need solutions fast.

That’s where this guide comes in. I’m going to share with you the five quick fixes that I, and many other arborists, reach for first when a Stihl chainsaw refuses to stay running. These aren’t exhaustive repairs, mind you, but they’re the most common culprits and the easiest to address in the field. I’ve spent years in the woods, and I’ve learned that a little preventative maintenance and a solid understanding of basic troubleshooting can save you a lot of time, money, and frustration.

A Little Story From the Woods

I remember one particularly grueling job in the Pacific Northwest. We were tasked with clearing a large stand of Douglas fir after a windstorm. Our crew was pushing hard to meet the deadline, and the pressure was on. Then, halfway through the second day, one of our Stihl MS 462 R C-Ms just died. Wouldn’t stay running. The air hung thick with the smell of pine, the whine of other saws filled the air, and the silence of the dead saw felt deafening.

Instead of panicking, I ran through these five quick fixes. Turns out, a clogged fuel filter was the culprit. A quick swap, and we were back in business in under 10 minutes. Saved the day! That experience cemented in my mind the importance of knowing these simple troubleshooting steps.

1. The Obvious Culprit: Check the Fuel

It might seem ridiculously simple, but trust me, it’s the first place to start. I’ve lost count of the times a “dead” chainsaw was simply out of gas or had stale fuel.

• The Problem: Chainsaws need a specific fuel mixture (usually a 50:1 ratio of gasoline to 2-cycle engine oil). Stale fuel can gum up the carburetor and prevent the engine from running smoothly, or at all.

• The Fix:

  1. Check the Fuel Level: Obvious, but crucial. Make sure there’s enough fuel in the tank.
  2. Inspect the Fuel: If the fuel smells old or looks discolored, drain it completely.
  3. Mix Fresh Fuel: Use high-quality gasoline (at least 89 octane) and a reputable 2-cycle engine oil at the correct ratio. Stihl recommends their own brand of oil, but any API TC-rated oil will work. Pay attention to the manufacturer’s recommendations.
  4. Pro Tip: I always carry a small container of pre-mixed fuel with me in the field. It eliminates the guesswork and ensures I’m using the correct ratio. I also add a fuel stabilizer to my fuel cans to extend the shelf life of the fuel. This is especially important if you don’t use your chainsaw regularly.

• Data Point: Studies have shown that gasoline can start to degrade in as little as 30 days, leading to poor engine performance and potential damage. Using fuel stabilizer can extend the shelf life to up to 24 months.

• Safety First: Always mix fuel outdoors in a well-ventilated area. Wear gloves and eye protection to avoid contact with fuel and oil.

2. Airflow is Key: Inspect the Air Filter

A clogged air filter restricts airflow to the engine, causing it to run lean and stall. This is especially common in dusty or dirty environments.

• The Problem: Sawdust, dirt, and debris can quickly clog the air filter, starving the engine of oxygen.
• The Fix:
  1. Locate the Air Filter: It’s usually under a cover on top of the engine. Consult your owner’s manual if you’re unsure.
  2. Remove the Filter: Carefully remove the air filter, being careful not to let any debris fall into the carburetor.
  3. Inspect the Filter: If the filter is dirty, clean it. You can use compressed air to blow out the debris or wash it with warm, soapy water. Make sure the filter is completely dry before reinstalling it.
  4. Replace the Filter: If the filter is damaged or excessively dirty, replace it with a new one.
  5. Pro Tip: I carry a spare air filter with me in the field. This allows me to quickly swap out a dirty filter without having to wait for it to dry. I also clean my air filter at the end of each day, especially if I’ve been working in a dusty environment.
• Data Point: A study by the US Forest Service found that a clogged air filter can reduce engine power by as much as 20%.
• Filter Types: Stihl chainsaws use various filter types. Some are simple felt filters, while others are more advanced HD2 filters. HD2 filters offer superior filtration and are more resistant to clogging. Check your owner’s manual for the correct replacement filter.

3. Fuel Delivery Issues: Check the Fuel Filter

Even with fresh fuel, a clogged fuel filter can prevent the engine from getting enough fuel to run properly.

• The Problem: The fuel filter sits inside the fuel tank and filters out debris before it reaches the carburetor. Over time, it can become clogged with dirt, sawdust, and other contaminants.

• The Fix:

  1. Locate the Fuel Filter: It’s usually attached to the end of a fuel line inside the fuel tank.
  2. Remove the Fuel Filter: Use a small hook or wire to pull the fuel line and filter out of the tank. Be careful not to damage the fuel line.
  3. Inspect the Filter: If the filter is dirty, clean it. You can try blowing it out with compressed air or soaking it in carburetor cleaner.
  4. Replace the Filter: If the filter is severely clogged or damaged, replace it with a new one.
  5. Pro Tip: I replace my fuel filter every six months, regardless of its condition. It’s a cheap and easy way to prevent fuel delivery problems. I also use a fuel line pick to carefully remove the filter without damaging the fuel line.

• Data Point: A restricted fuel filter can cause the engine to run lean, which can lead to overheating and engine damage.

• Fuel Line Inspection: While you have the fuel filter out, inspect the fuel lines for cracks or leaks. Replace them if necessary. Cracked fuel lines can cause air leaks, which can also prevent the engine from running properly.

4. Spark of Life: Inspect the Spark Plug

The spark plug is responsible for igniting the fuel-air mixture in the cylinder. A fouled or damaged spark plug can prevent the engine from starting or running properly.

• The Problem: Spark plugs can become fouled with carbon deposits, oil, or fuel. They can also be damaged by overheating or physical impact.
• The Fix:
  1. Locate the Spark Plug: It’s usually located on the side of the engine, under a rubber boot.
  2. Remove the Spark Plug: Use a spark plug wrench to remove the spark plug.
  3. Inspect the Spark Plug: Look for signs of fouling, damage, or wear. The electrode should be clean and free of deposits. The insulator should be intact and free of cracks.
  4. Clean the Spark Plug: If the spark plug is fouled with carbon deposits, you can try cleaning it with a wire brush or spark plug cleaner.
  5. Gap the Spark Plug: Use a spark plug gapping tool to ensure that the gap between the electrode and the ground electrode is correct. The correct gap is usually specified in your owner’s manual. Typically this is around 0.5mm (0.020 inches).
  6. Replace the Spark Plug: If the spark plug is damaged or excessively worn, replace it with a new one.
  7. Pro Tip: I carry a spare spark plug with me in the field. This allows me to quickly replace a fouled spark plug without having to clean it. I also use a spark plug tester to check the spark plug’s performance before installing it.
• Data Point: A properly functioning spark plug is essential for optimal engine performance. A fouled or damaged spark plug can reduce engine power, increase fuel consumption, and cause the engine to misfire.
• Spark Plug Types: Stihl chainsaws typically use NGK or Bosch spark plugs. Check your owner’s manual for the correct spark plug type for your model. Using the wrong spark plug can damage the engine.

5. The Carburetor Conundrum: Carburetor Adjustment (with Caution)

This is where things get a bit more technical, and I want to emphasize the “with caution” part. A carburetor that’s out of adjustment can cause a variety of problems, including stalling, poor idling, and lack of power.

• The Problem: The carburetor is responsible for mixing fuel and air in the correct proportions. Over time, the carburetor can become out of adjustment due to wear, vibration, or changes in altitude.

• The Fix:

  1. Locate the Carburetor Adjustment Screws: These are usually located on the side of the carburetor. There are typically three adjustment screws:
     • L (Low Speed): Controls the fuel-air mixture at idle and low speeds.
     • H (High Speed): Controls the fuel-air mixture at high speeds.
     • LA (Idle Speed): Controls the engine’s idle speed.
  2. Adjust the Idle Speed (LA): Start the engine and let it warm up. Turn the LA screw until the engine idles smoothly without stalling.
  3. Adjust the Low Speed (L): With the engine idling, slowly turn the L screw clockwise until the engine starts to stumble or stall. Then, slowly turn the L screw counterclockwise until the engine idles smoothly and accelerates cleanly.
  4. Adjust the High Speed (H): This is where caution is needed. The H screw controls the fuel-air mixture at high speeds. Adjusting this screw incorrectly can damage the engine. If you’re not comfortable adjusting the H screw, it’s best to take your chainsaw to a qualified technician.
  5. Listen to the Engine: The engine should sound crisp and responsive. If it sounds sluggish or hesitant, the carburetor may need further adjustment.
  6. Pro Tip: I recommend marking the original positions of the adjustment screws before making any changes. This will allow you to easily return the carburetor to its original settings if you make a mistake. I also use a small screwdriver with a fine tip to make precise adjustments.

• Data Point: A properly adjusted carburetor can improve engine performance, reduce fuel consumption, and extend engine life. However, an improperly adjusted carburetor can cause engine damage.

• The Importance of a Tachometer: For precise carburetor adjustments, especially on professional-grade saws, a tachometer is invaluable. It allows you to accurately measure the engine RPM and ensure that it’s within the manufacturer’s specifications. Stihl’s M-Tronic system (found on some models like the MS 462 R C-M) automates carburetor adjustments, making it less critical to manually adjust the H screw.
• When to Seek Professional Help: If you’ve tried these quick fixes and your chainsaw still won’t stay running, it’s time to take it to a qualified technician. There may be a more serious problem with the engine, such as a damaged piston, cylinder, or crankshaft.

Beyond the Quick Fixes: Preventative Maintenance is Key

These five quick fixes can get you back in business in a pinch, but the best way to avoid chainsaw problems is to practice preventative maintenance. Here are a few tips:

• Clean Your Chainsaw Regularly: Remove sawdust and debris from the engine, air filter, and carburetor after each use.
• Sharpen Your Chain Regularly: A sharp chain cuts more efficiently and reduces strain on the engine.
• Lubricate the Chain Properly: Use a high-quality bar and chain oil to keep the chain lubricated.
• Store Your Chainsaw Properly: Store your chainsaw in a clean, dry place. Drain the fuel tank before storing it for extended periods.
• Follow the Manufacturer’s Recommendations: Consult your owner’s manual for specific maintenance recommendations for your chainsaw model.

Wood Processing: A Quick Dive into Technical Specs

Since we’re talking chainsaws, let’s touch on some wood processing specifics. The performance of your chainsaw is directly related to the type of wood you’re cutting and how you’re cutting it.

• Wood Density and Chainsaw Selection: Different wood species have different densities, which affects how easily they can be cut. Softwoods like pine and fir are easier to cut than hardwoods like oak and maple. For larger hardwood projects, you’ll need a more powerful chainsaw.
  • Data Point: Douglas fir has a density of around 33 lbs/cubic foot, while red oak has a density of around 45 lbs/cubic foot. This difference in density translates to a significant difference in cutting resistance.
• Log Diameter and Chainsaw Bar Length: The diameter of the logs you’re cutting will determine the appropriate bar length for your chainsaw. As a general rule, the bar length should be at least two inches longer than the diameter of the logs you’re cutting.
  • Data Point: Using a bar that’s too short can be dangerous and inefficient. It can also put unnecessary strain on the engine.
• Wood Moisture Content and Firewood Preparation: The moisture content of the wood you’re cutting will affect how easily it splits and how well it burns. Firewood should be seasoned (dried) to a moisture content of 20% or less before burning.
  • Data Point: Green wood can have a moisture content of 50% or more. Burning green wood is inefficient and produces more smoke and creosote.
  • Technical Requirement: Firewood moisture content should be below 20% for efficient burning, ideally between 15%-20%. Use a moisture meter to verify.
• Log Dimensions and Cord Volume: When selling firewood, it’s important to know how to measure log dimensions and calculate cord volume. A standard cord of firewood is 4 feet high, 4 feet wide, and 8 feet long, for a total volume of 128 cubic feet.
  • Data Point: A “face cord” or “rick” is typically 4 feet high and 8 feet long, but the depth can vary. Be sure to specify the depth when selling firewood by the face cord.
  • Technical Requirement: Ensure accurate measurement of log lengths and stack heights to comply with local regulations on firewood sales.
• Cutting Techniques: Different cutting techniques can be used to maximize efficiency and minimize waste. For example, bucking logs into shorter lengths can make them easier to split and handle.
  • Data Point: Using proper cutting techniques can reduce the amount of sawdust produced, which can save you time and money.

Safety Equipment: Non-Negotiable

No discussion about chainsaws is complete without emphasizing safety. Chainsaws are powerful tools, and they can be dangerous if used improperly. Always wear appropriate safety equipment, including:

• Eye Protection: Safety glasses or a face shield to protect your eyes from flying debris.
• Hearing Protection: Earplugs or earmuffs to protect your hearing from the loud noise of the chainsaw.
• Head Protection: A hard hat to protect your head from falling branches or debris.
• Hand Protection: Gloves to protect your hands from cuts and abrasions.
• Leg Protection: Chainsaw chaps or pants to protect your legs from accidental cuts.
• Foot Protection: Steel-toed boots to protect your feet from falling logs or debris.

Final Thoughts

Keeping your Stihl chainsaw running smoothly is a combination of understanding its basic mechanics, practicing preventative maintenance, and knowing how to troubleshoot common problems. By following these five quick fixes, you’ll be well-equipped to tackle most minor issues in the field. Remember to always prioritize safety and seek professional help when needed. The woods can be a rewarding place to work, but they demand respect and preparation. Happy cutting!

Learn more