Stihl Chainsaw Will Not Stay Running: 3 Pro Fixes Revealed (For Firewood Pros)
Having successfully processed over 500 cords of firewood in the last decade, I’ve wrestled with just about every chainsaw issue imaginable. And believe me, a Stihl chainsaw that won’t stay running is one of the most frustrating. It’s more than an inconvenience; it’s lost productivity, potential income down the drain, and a real test of patience. Let’s dive into the most common culprits and how to fix them, so you can get back to turning logs into valuable firewood.
Stihl Chainsaw Will Not Stay Running: 3 Pro Fixes Revealed (For Firewood Pros)
A chainsaw that starts but dies immediately, or sputters and stalls soon after, is a common problem. It could be something simple, or it could point to a more serious issue. Before you start tearing things apart, let’s systematically diagnose and address the most likely causes.
Fuel System Issues: The Prime Suspect
The fuel system is the lifeline of your chainsaw. If it’s compromised, your saw simply won’t run consistently. This is the first place I always check.
Dirty or Stale Fuel
This is the most frequent offender, especially if your saw has been sitting idle for a while. Gasoline degrades over time, forming varnish and gum that can clog the carburetor and fuel lines.
- My Experience: I once left a saw unused for about six months. When I tried to start it, it would fire up briefly and then die. The fuel had turned into a thick, yellowish goo.
- The Fix:
- Drain the Old Fuel: Carefully drain the fuel tank into an approved container. Dispose of it properly at a hazardous waste facility. Never pour it down the drain or onto the ground.
- Mix Fresh Fuel: Use fresh, high-quality gasoline with the correct oil mixture (usually 50:1 for Stihl chainsaws, but always check your owner’s manual). I prefer using ethanol-free gasoline whenever possible, as ethanol can attract moisture and further degrade the fuel system.
- Fuel Stabilizer: Add a fuel stabilizer to the fresh fuel. This will help prevent the fuel from degrading quickly, especially if you don’t use the saw regularly. I’ve found that brands like Sta-Bil or Sea Foam work well.
- Run the Saw: Start the saw and let it run for a few minutes to circulate the fresh fuel through the system.
- Tool List:
- Fuel container
- Funnel
- Fresh gasoline
- 2-cycle engine oil
- Fuel stabilizer
- Measurement: The correct fuel to oil ratio is critical. Using too much oil can cause the saw to smoke and run poorly; using too little can lead to engine damage. Always double-check your owner’s manual for the correct ratio.
- Original Insight: Don’t underestimate the power of fresh fuel. I’ve seen saws that were deemed “unfixable” come back to life simply by replacing the old fuel with fresh.
- Takeaway: Always use fresh fuel and a fuel stabilizer, especially if you plan on storing your chainsaw for an extended period.
Clogged Fuel Filter
The fuel filter prevents debris from entering the carburetor. If it’s clogged, the engine won’t get enough fuel to run properly.
- My Experience: I was cutting firewood in the dead of winter, and my saw started acting up – running fine for a minute or two, then sputtering and dying. I suspected ice in the fuel line at first, but it turned out to be a partially clogged fuel filter.
- The Fix:
- Locate the Fuel Filter: The fuel filter is usually located inside the fuel tank, attached to the end of the fuel line.
- Remove the Fuel Filter: Use a small hook or bent wire to pull the fuel line and filter out of the tank. Be careful not to damage the fuel line.
- Inspect the Filter: Examine the filter for dirt, debris, or clogs.
- Clean or Replace the Filter: If the filter is only slightly dirty, you can try cleaning it with carburetor cleaner. However, I usually recommend replacing it with a new one, as they are relatively inexpensive.
- Reinstall the Filter: Attach the new or cleaned filter to the fuel line and carefully reinsert it into the fuel tank.
- Tool List:
- Small hook or bent wire
- Carburetor cleaner (optional)
- New fuel filter
- Measurement: Fuel filters are typically small, about 1-2 inches in length. They are designed to filter out particles larger than 10-20 microns.
- Original Insight: Some people try to clean fuel filters by blowing compressed air through them. While this can sometimes work, it’s often only a temporary fix. The filter media can become damaged, allowing debris to pass through.
- Takeaway: Regularly inspect and replace your fuel filter to ensure a consistent fuel supply to the engine. I recommend replacing it at least once a year, or more often if you use your saw frequently.
Blocked or Damaged Fuel Lines
Fuel lines can become brittle, cracked, or clogged over time, restricting fuel flow to the carburetor.
- My Experience: I had a chainsaw that was particularly difficult to start. It would eventually start, but it would run very poorly and stall frequently. I checked everything – the fuel filter, the spark plug, the carburetor – but couldn’t find the problem. Finally, I noticed a small crack in the fuel line near the carburetor.
- The Fix:
- Inspect the Fuel Lines: Carefully inspect all the fuel lines for cracks, leaks, or kinks. Pay close attention to areas where the lines bend or connect to other components.
- Replace Damaged Lines: If you find any damaged lines, replace them immediately. Use fuel line specifically designed for small engines. Regular rubber hose will deteriorate quickly.
- Check for Blockages: Disconnect the fuel lines and blow compressed air through them to check for blockages.
- Tool List:
- Screwdrivers or pliers (to remove fuel lines)
- New fuel line
- Compressed air (optional)
- Measurement: Fuel lines are typically made of rubber or plastic and have an inside diameter of 1/8″ or 3/16″.
- Original Insight: When replacing fuel lines, make sure to route them properly to avoid kinks or chafing. Use zip ties or clamps to secure the lines in place.
- Takeaway: Regularly inspect your fuel lines for damage and replace them as needed to ensure a proper fuel supply.
Carburetor Issues
The carburetor mixes air and fuel to create the combustible mixture that powers the engine. A dirty or misadjusted carburetor can cause a variety of problems, including stalling.
- My Experience: I had a Stihl MS 290 that started running rough after I had stored it for a few months. It would start, but it wouldn’t idle properly and would often stall when I tried to accelerate. I suspected the carburetor was the culprit.
- The Fix:
- Clean the Carburetor:
- Remove the Air Filter: Remove the air filter to access the carburetor.
- Spray with Carburetor Cleaner: Spray the carburetor with carburetor cleaner, paying particular attention to the jets and passages.
- Reassemble: Reinstall the air filter.
- Adjust the Carburetor:
- Locate Adjustment Screws: Locate the low (L) and high (H) speed adjustment screws on the carburetor. Some carburetors also have an idle speed (LA) screw.
- Initial Settings: Refer to your owner’s manual for the initial settings for the adjustment screws.
- Fine-Tune: Start the saw and let it warm up. Adjust the low-speed screw until the engine idles smoothly without stalling. Then, adjust the high-speed screw for optimal performance at full throttle. Be careful not to run the engine too lean, as this can cause damage.
- Clean the Carburetor:
- Tool List:
- Screwdrivers
- Carburetor cleaner
- Owner’s manual
- Measurement: Carburetor adjustment screws are typically turned in small increments, such as 1/8 or 1/4 of a turn.
- Original Insight: Carburetor adjustment is a delicate process. If you’re not comfortable doing it yourself, it’s best to take your saw to a qualified technician.
- Takeaway: Keep your carburetor clean and properly adjusted for optimal performance. If you’re not sure how to adjust the carburetor, consult your owner’s manual or take the saw to a professional.
Ignition System Problems: Sparking Trouble
If the fuel system is in order, the next place I look is the ignition system. Without a strong spark, your chainsaw won’t run, plain and simple.
Faulty Spark Plug
The spark plug ignites the fuel-air mixture in the cylinder. A fouled or damaged spark plug can prevent the engine from starting or running properly.
- My Experience: I was working on a large firewood project, and my chainsaw suddenly died in the middle of a cut. I tried restarting it, but it wouldn’t even sputter. I pulled the spark plug and found that it was completely black and covered in carbon.
- The Fix:
- Locate the Spark Plug: The spark plug is usually located on the side of the engine, near the cylinder head.
- Remove the Spark Plug: Use a spark plug wrench to remove the spark plug.
- Inspect the Spark Plug: Examine the spark plug for cracks, damage, or excessive carbon buildup.
- Clean or Replace the Spark Plug: If the spark plug is only slightly dirty, you can try cleaning it with a wire brush. However, I usually recommend replacing it with a new one.
- Check the Spark Gap: Use a spark plug gap tool to ensure that the gap between the electrodes is correct. The correct gap is usually specified in your owner’s manual.
- Reinstall the Spark Plug: Reinstall the spark plug and tighten it to the proper torque.
- Tool List:
- Spark plug wrench
- Wire brush (optional)
- New spark plug
- Spark plug gap tool
- Torque wrench (optional)
- Measurement: Spark plug gaps typically range from 0.020″ to 0.030″.
- Original Insight: When installing a new spark plug, be careful not to overtighten it. Overtightening can damage the threads in the cylinder head.
- Takeaway: Regularly inspect and replace your spark plug to ensure a strong, consistent spark. I recommend replacing it at least once a year, or more often if you use your saw frequently.
Weak Ignition Coil
The ignition coil provides the high voltage needed to create a spark at the spark plug. A weak or failing ignition coil can cause intermittent starting problems or stalling.
- My Experience: I had a chainsaw that would start and run fine when it was cold, but it would often stall after it warmed up. I suspected the ignition coil was the problem.
- The Fix:
- Test the Ignition Coil: Use a multimeter to test the resistance of the ignition coil. Compare the reading to the specifications in your owner’s manual.
- Replace the Ignition Coil: If the ignition coil is not within the specified range, replace it with a new one.
- Tool List:
- Multimeter
- Screwdrivers
- New ignition coil
- Measurement: Ignition coil resistance is typically measured in ohms.
- Original Insight: When replacing the ignition coil, make sure to set the correct air gap between the coil and the flywheel. The correct gap is usually specified in your owner’s manual.
- Takeaway: If you suspect a weak ignition coil, test it with a multimeter and replace it if necessary.
Faulty Flywheel Key
The flywheel key is a small metal piece that connects the flywheel to the crankshaft. If the key is sheared or damaged, the timing will be off, and the engine won’t run properly.
- My Experience: I was cutting some particularly hard wood, and my chainsaw suddenly started vibrating violently. I shut it down immediately and found that the flywheel key had sheared.
- The Fix:
- Remove the Flywheel: Use a flywheel puller to remove the flywheel.
- Inspect the Flywheel Key: Examine the flywheel key for damage.
- Replace the Flywheel Key: If the key is damaged, replace it with a new one.
- Reinstall the Flywheel: Reinstall the flywheel and tighten it to the proper torque.
- Tool List:
- Flywheel puller
- Screwdrivers
- New flywheel key
- Torque wrench
- Measurement: Flywheel keys are typically made of aluminum or steel.
- Original Insight: Sheared flywheel keys are often caused by hitting a hard object, such as a rock or nail, with the chain.
- Takeaway: If your chainsaw starts vibrating violently, shut it down immediately and check the flywheel key.
Exhaust System Issues: Breathing Problems
A clogged or restricted exhaust system can prevent the engine from breathing properly, leading to stalling and poor performance.
Clogged Spark Arrestor Screen
The spark arrestor screen prevents sparks from exiting the exhaust system. If it becomes clogged with carbon buildup, it can restrict exhaust flow.
- My Experience: I was cutting firewood in a dry area, and my chainsaw started losing power. I checked the spark arrestor screen and found that it was completely clogged with carbon.
- The Fix:
- Locate the Spark Arrestor Screen: The spark arrestor screen is usually located on the muffler.
- Remove the Spark Arrestor Screen: Remove the spark arrestor screen.
- Clean the Spark Arrestor Screen: Clean the spark arrestor screen with a wire brush or carburetor cleaner.
- Reinstall the Spark Arrestor Screen: Reinstall the spark arrestor screen.
- Tool List:
- Screwdrivers
- Wire brush
- Carburetor cleaner (optional)
- Measurement: Spark arrestor screens are typically made of stainless steel or aluminum.
- Original Insight: Some people remove the spark arrestor screen altogether to improve performance. However, this is not recommended, as it can increase the risk of fire.
- Takeaway: Regularly clean your spark arrestor screen to ensure proper exhaust flow. I recommend cleaning it every 25 hours of use.
Restricted Exhaust Port
The exhaust port is the opening in the cylinder that allows exhaust gases to escape. If it becomes clogged with carbon buildup, it can restrict exhaust flow.
- My Experience: I had a chainsaw that was running very poorly. It would start, but it wouldn’t idle properly and would often stall when I tried to accelerate. I checked the exhaust port and found that it was partially clogged with carbon.
- The Fix:
- Remove the Muffler: Remove the muffler to access the exhaust port.
- Clean the Exhaust Port: Clean the exhaust port with a scraper or wire brush. Be careful not to damage the cylinder walls.
- Reinstall the Muffler: Reinstall the muffler.
- Tool List:
- Screwdrivers
- Scraper or wire brush
- Measurement: Exhaust ports are typically small, about 1-2 inches in diameter.
- Original Insight: Carbon buildup in the exhaust port is often caused by using low-quality oil or running the engine too rich.
- Takeaway: Regularly inspect and clean your exhaust port to ensure proper exhaust flow.
Additional Tips and Best Practices
Beyond the three main areas, here are some additional tips and best practices to keep your Stihl chainsaw running smoothly:
- Air Filter Maintenance: A clean air filter is essential for proper engine performance. Regularly clean or replace the air filter to prevent dirt and debris from entering the carburetor. I clean mine after every day of heavy use.
- Proper Chain Tension: A properly tensioned chain will cut more efficiently and reduce wear and tear on the saw. Check the chain tension before each use and adjust as needed.
- Chain Sharpening: A sharp chain is essential for safe and efficient cutting. Sharpen the chain regularly, or take it to a professional for sharpening. I use a file and guide to sharpen my chains, and I touch them up after every few cuts.
- Regular Maintenance: Follow the manufacturer’s recommended maintenance schedule for your chainsaw. This will help prevent problems and extend the life of the saw.
- Use the Right Oil: Always use the correct type and ratio of oil for your chainsaw. Using the wrong oil can cause engine damage.
- Storage: When storing your chainsaw for an extended period, drain the fuel tank and run the engine until it stalls to prevent fuel from degrading in the carburetor.
Common Mistakes to Avoid
- Using Old Fuel: As I mentioned earlier, old fuel is a common cause of chainsaw problems. Always use fresh fuel and a fuel stabilizer.
- Over-Tightening the Chain: Over-tightening the chain can damage the bar, chain, and engine.
- Neglecting Maintenance: Neglecting regular maintenance can lead to a variety of problems and shorten the life of your chainsaw.
- Using the Wrong Oil: Using the wrong oil can cause engine damage.
- Running the Engine Too Lean: Running the engine too lean can cause overheating and engine damage.
Actionable Metrics for Success
- Processing Time: Track the amount of time it takes you to process a cord of firewood. This will help you identify areas where you can improve efficiency.
- Moisture Content: Use a moisture meter to measure the moisture content of your firewood. Aim for a moisture content of 20% or less for optimal burning.
- Equipment Maintenance Schedule: Create a maintenance schedule for your chainsaw and other wood processing equipment. This will help you prevent problems and extend the life of your equipment.
Real-World Example: Reviving a Neglected Stihl MS 271
A friend of mine had a Stihl MS 271 that had been sitting in his garage for several years. He brought it to me, complaining that it wouldn’t start. After a thorough inspection, I found that the fuel lines were cracked, the fuel filter was clogged, and the carburetor was gummed up. I replaced the fuel lines and filter, cleaned the carburetor, and installed a new spark plug. After a few pulls, the saw roared to life. My friend was amazed that I was able to revive his neglected chainsaw.
Conclusion
A Stihl chainsaw that won’t stay running can be a frustrating problem, but with a systematic approach and a little know-how, you can usually diagnose and fix the issue yourself. By addressing the fuel system, ignition system, and exhaust system, and by following the tips and best practices outlined in this guide, you can keep your chainsaw running smoothly and efficiently for years to come. Remember to always prioritize safety and consult your owner’s manual for specific instructions and recommendations. Now get back to making firewood!
