Starting Stihl MS 250 Troubleshooting Tips (7 Pro Fixes)
As someone who’s spent countless hours in the woods, from the crisp autumns of New England to the humid summers of the Pacific Northwest, I understand the frustration of a balky chainsaw. The Stihl MS 250 is a workhorse, a favorite among homeowners and professionals alike for its balance of power and portability. But like any machine, it can have its hiccups. This guide, “Starting Stihl MS 250 Troubleshooting Tips (7 Pro Fixes),” is designed to help you diagnose and resolve common starting issues with your MS 250, getting you back to cutting wood quickly and safely. I’ll share not just the fixes, but the why behind them, drawing on my own experiences and insights from years of working with chainsaws.
Addressing Climate-Specific Needs
Before we dive in, it’s crucial to acknowledge that climate plays a significant role in chainsaw performance. In colder climates, fuel mixtures can be more sensitive, and condensation can form in the fuel tank. In humid environments, air filters can clog more quickly, and carburetor adjustments may need tweaking. If you live in a region with extreme temperatures or humidity, pay extra attention to fuel storage, air filter maintenance, and carburetor settings, as these are often the first culprits when a chainsaw refuses to start.
Diagnosing the Problem: The 7 Pro Fixes
When your Stihl MS 250 refuses to start, it’s tempting to throw your hands up in frustration. But systematic troubleshooting is key. I’ve broken down the most common starting problems into seven manageable areas, each with its own set of fixes.
1. Fuel Delivery Issues: Is the Engine Getting Gas?
This is the most common reason why chainsaws fail to start. It’s about ensuring the engine is getting the fuel it needs to fire.
Key Concepts:
- Fuel Mixture: Stihl MS 250s typically require a 50:1 fuel-to-oil ratio. Using the wrong mixture can lead to poor performance and engine damage. I always recommend using a high-quality two-stroke oil specifically designed for chainsaws. I’ve seen engines seize up from using the wrong oil, so don’t skimp on this.
- Fuel Filter: Located inside the fuel tank, the fuel filter prevents debris from entering the carburetor. A clogged filter restricts fuel flow.
- Fuel Lines: These lines carry fuel from the tank to the carburetor. They can crack, become brittle, or get clogged over time.
- Carburetor: The carburetor mixes fuel and air in the correct proportions for combustion. It’s a complex component, and even small adjustments can make a big difference.
Step-by-Step Guide:
- Check the Fuel Tank: Make sure there’s enough fuel and that it’s fresh. Stale fuel can lose its volatility and prevent the engine from starting. I always recommend using fuel stabilizer, especially if the saw will be stored for an extended period. I learned this the hard way after a winter of neglecting my saw, only to find it wouldn’t start in the spring.
- Inspect the Fuel Filter:
- Location: Inside the fuel tank, attached to the fuel line.
- Procedure: Use a small hook or wire to pull the fuel filter out of the tank. Examine it for debris.
- Fix: If the filter is dirty, replace it. Fuel filters are inexpensive and should be replaced annually, or more frequently if you’re cutting a lot of dirty wood. I like to keep a few spares on hand.
- Tool Specification: Fuel filter removal tool (optional, but makes the job easier).
- Cost: $5-$10
- Examine the Fuel Lines:
- Procedure: Check the fuel lines for cracks, leaks, or kinks. Pay close attention to the connections at the fuel tank and carburetor.
- Fix: Replace any damaged fuel lines. Cracked fuel lines can cause air leaks, which will prevent the engine from starting. I once had a hairline crack in a fuel line that was almost invisible, but it was enough to cause starting problems.
- Material Specs: Use fuel lines specifically designed for chainsaws, as they are resistant to fuel and oil.
- Cost: $10-$20
- Prime the Carburetor:
- Procedure: Press the primer bulb (usually a clear bubble on the side of the carburetor) several times until fuel is visible in the bulb. This helps draw fuel into the carburetor.
- Note: If the primer bulb doesn’t fill with fuel, there’s likely a blockage in the fuel line or filter.
- Check the Carburetor Adjustment Screws:
- Key Concept: The carburetor has adjustment screws for high (H) and low (L) speed settings. These screws control the fuel-to-air mixture.
- Procedure: Locate the H and L screws on the carburetor. Use a small screwdriver to adjust the L screw slightly. Turn it clockwise to lean the mixture (less fuel) or counterclockwise to richen the mixture (more fuel).
- Caution: Make small adjustments (1/8 of a turn) and try starting the saw after each adjustment. Over-adjusting the carburetor can damage the engine.
- Original Insight: I’ve found that carburetors often need slight adjustments based on altitude. Higher altitudes require leaner mixtures.
Personalized Story:
I remember one time, I was helping a friend clear some brush on his property. His Stihl MS 250 wouldn’t start, and he was about to give up. After checking the fuel filter and lines, I noticed the primer bulb wasn’t filling with fuel. I suspected a blockage, so I carefully removed the fuel line from the carburetor and blew compressed air through it. Sure enough, a small piece of debris came out. After reassembling everything, the saw started right up. It’s often the simplest things that cause the biggest problems.
2. Ignition System: Is There Spark?
The ignition system is responsible for creating the spark that ignites the fuel-air mixture. If there’s no spark, the engine won’t start.
Key Concepts:
- 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.
- Ignition Coil: The ignition coil generates the high voltage needed to create a spark at the spark plug.
- Flywheel: The flywheel rotates and generates the electrical current needed for the ignition coil.
- Air Gap: The air gap is the distance between the ignition coil and the flywheel. It must be set correctly for the ignition system to function properly.
Step-by-Step Guide:
- Check the Spark Plug:
- Location: On the side of the engine, connected to the spark plug wire.
- Procedure: Remove the spark plug using a spark plug wrench. Inspect the spark plug for fouling (carbon buildup), cracks, or damage.
- Fix: If the spark plug is fouled, clean it with a wire brush or replace it. If it’s cracked or damaged, replace it.
- Tool Specification: Spark plug wrench (typically 19mm).
- Cost: $5-$10
- Original Insight: I’ve found that using the correct spark plug gap is crucial for optimal performance. Consult your Stihl MS 250 owner’s manual for the correct gap specification.
- Test for Spark:
- Procedure: Reconnect the spark plug to the spark plug wire. Ground the spark plug against the engine block (make sure the metal part of the spark plug is touching the metal of the engine). Pull the starter cord. You should see a spark jump across the spark plug gap.
- Caution: Be careful not to touch the spark plug while pulling the starter cord, as you could get an electric shock.
- No Spark: If there’s no spark, the ignition coil may be faulty.
- Check the Ignition Coil:
- Procedure: The ignition coil is located near the flywheel. Inspect the coil for damage or corrosion.
- Fix: If the coil is damaged, replace it.
- Tool Specification: Screwdrivers, multimeter (optional, for testing coil resistance).
- Cost: $20-$50
- Check the Air Gap:
- Procedure: The air gap is the distance between the ignition coil and the flywheel. It must be set correctly for the ignition system to function properly. Use a feeler gauge to measure the air gap.
- Fix: Adjust the air gap according to the specifications in your Stihl MS 250 owner’s manual. Typically, the air gap should be around 0.012-0.016 inches (0.3-0.4 mm).
- Tool Specification: Feeler gauge.
- Original Insight: I’ve found that a slightly wider air gap can sometimes improve starting in cold weather.
Case Study:
I once had a Stihl MS 250 that wouldn’t start, even after replacing the spark plug. I tested for spark, and there was none. I suspected the ignition coil, but I wanted to be sure before replacing it. I used a multimeter to test the coil’s resistance, and it was out of spec. I replaced the coil, and the saw started right up. This experience taught me the importance of using a multimeter to diagnose electrical problems.
3. Air Intake: Is the Engine Getting Enough Air?
The engine needs a proper air-fuel mixture to start and run. A clogged air filter can restrict airflow, leading to starting problems.
Key Concepts:
- Air Filter: The air filter prevents dust and debris from entering the carburetor and engine. A clogged air filter restricts airflow.
- Choke: The choke restricts airflow to enrich the fuel-air mixture for cold starting.
Step-by-Step Guide:
- Check the Air Filter:
- Location: Under the air filter cover, typically on top of the engine.
- Procedure: Remove the air filter cover and inspect the air filter for dirt and debris.
- Fix: If the air filter is dirty, clean it with soap and water or replace it. I recommend cleaning the air filter regularly, especially if you’re cutting in dusty conditions.
- Material Specs: Some air filters can be cleaned; others must be replaced. Consult your Stihl MS 250 owner’s manual.
- Cost: $5-$15
- Original Insight: I’ve found that using compressed air to clean an air filter can damage it. It’s better to wash it with soap and water and let it dry completely before reinstalling it.
- Check the Choke:
- Procedure: Make sure the choke is in the correct position for starting. For cold starting, the choke should be closed (fully engaged). Once the engine starts, gradually open the choke.
- Note: Over-choking the engine can flood it, making it difficult to start. If you suspect the engine is flooded, remove the spark plug and pull the starter cord several times to clear the excess fuel.
Personalized Story:
I once had a Stihl MS 250 that would start, but it would immediately die. I checked the fuel and spark, and everything seemed fine. Then I remembered that I hadn’t cleaned the air filter in a while. I removed the air filter, and it was completely clogged with sawdust. After cleaning the air filter, the saw ran perfectly. This experience taught me the importance of regular air filter maintenance.
4. Exhaust System: Is the Exhaust Flowing Freely?
A blocked exhaust port or muffler can prevent the engine from starting or running properly.
Key Concepts:
- Exhaust Port: The exhaust port allows exhaust gases to escape from the cylinder.
- Muffler: The muffler reduces noise and directs exhaust gases away from the operator.
- Carbon Buildup: Over time, carbon can build up in the exhaust port and muffler, restricting exhaust flow.
Step-by-Step Guide:
- Check the Exhaust Port:
- Procedure: Remove the muffler and inspect the exhaust port for carbon buildup.
- Fix: If there’s carbon buildup, carefully scrape it away with a small tool. Be careful not to damage the cylinder walls.
- Tool Specification: Scraper, wire brush.
- Check the Muffler:
- Procedure: Inspect the muffler for blockage.
- Fix: If the muffler is blocked, clean it with a wire brush or replace it.
- Original Insight: I’ve found that using a high-quality two-stroke oil can help reduce carbon buildup in the exhaust system.
Case Study:
I once had a Stihl MS 250 that was running poorly and lacked power. I suspected a blocked exhaust, so I removed the muffler and inspected the exhaust port. It was completely clogged with carbon. I carefully scraped away the carbon, and the saw ran like new. This experience taught me the importance of checking the exhaust system when troubleshooting performance problems.
5. Compression: Is the Engine Compressing the Fuel-Air Mixture?
Compression is essential for the engine to ignite the fuel-air mixture. Low compression can prevent the engine from starting.
Key Concepts:
- Cylinder: The cylinder is the part of the engine where the fuel-air mixture is compressed and ignited.
- Piston: The piston moves up and down inside the cylinder, compressing the fuel-air mixture.
- Piston Rings: The piston rings seal the piston against the cylinder walls, preventing compression loss.
- Compression Tester: A compression tester measures the pressure inside the cylinder.
Step-by-Step Guide:
- Perform a Compression Test:
- Procedure: Remove the spark plug and screw a compression tester into the spark plug hole. Pull the starter cord several times. The compression tester will measure the pressure inside the cylinder.
- Specification: A healthy Stihl MS 250 should have a compression reading of at least 120 PSI (pounds per square inch).
- Tool Specification: Compression tester.
- Cost: $20-$50
- Low Compression: If the compression reading is below 120 PSI, there may be a problem with the piston rings, cylinder, or valves.
- Inspect the Cylinder and Piston:
- Procedure: If the compression is low, you may need to remove the cylinder head and inspect the cylinder and piston for damage.
- Fix: If the cylinder or piston is damaged, you may need to replace them. This is a more complex repair that may require professional assistance.
Original Insight: I’ve found that using a fuel stabilizer can help prevent corrosion inside the cylinder, which can lead to compression loss.
6. Starter Mechanism: Is the Starter Engaging Properly?
The starter mechanism is responsible for turning the engine over so it can start. If the starter is not engaging properly, the engine won’t start.
Key Concepts:
- Starter Cord: The starter cord is pulled to turn the engine over.
- Recoil Spring: The recoil spring retracts the starter cord after it’s pulled.
- Pawls: The pawls engage with the flywheel to turn the engine over.
Step-by-Step Guide:
- Check the Starter Cord:
- Procedure: Inspect the starter cord for fraying or damage.
- Fix: If the starter cord is frayed or damaged, replace it.
- Cost: $5-$10
- Check the Recoil Spring:
- Procedure: If the starter cord doesn’t retract properly, the recoil spring may be broken or weak.
- Fix: Replace the recoil spring.
- Cost: $10-$20
- Check the Pawls:
- Procedure: Inspect the pawls for wear or damage. The pawls are small levers that engage with the flywheel to turn the engine over.
- Fix: If the pawls are worn or damaged, replace them.
Personalized Story:
I once had a Stihl MS 250 that wouldn’t start because the pawls were worn. The starter cord would pull, but the engine wouldn’t turn over. I replaced the pawls, and the saw started right up. This experience taught me the importance of inspecting the starter mechanism when troubleshooting starting problems.
7. Flooding: Is There Too Much Fuel in the Cylinder?
Flooding occurs when there’s too much fuel in the cylinder, preventing the engine from starting.
Key Concepts:
- Flooded Engine: An engine is flooded when there’s too much fuel in the cylinder.
- Spark Plug Fouling: A flooded engine can foul the spark plug, preventing it from sparking.
Step-by-Step Guide:
- Identify a Flooded Engine:
- Symptoms: The engine won’t start, and you may smell fuel.
- Clear a Flooded Engine:
- Procedure:
- Remove the spark plug.
- Pull the starter cord several times to clear the excess fuel from the cylinder.
- Dry the spark plug.
- Reinstall the spark plug.
- Try starting the engine again, without using the choke.
- Original Insight: I’ve found that sometimes, simply waiting a few minutes can allow the excess fuel to evaporate, allowing the engine to start.
- Procedure:
Preventing Future Starting Problems
Prevention is always better than cure. Here are some tips for preventing future starting problems with your Stihl MS 250:
- Use Fresh Fuel: Use fresh, high-quality fuel and mix it with the correct amount of two-stroke oil.
- Use Fuel Stabilizer: Add fuel stabilizer to the fuel, especially if you’re storing the saw for an extended period.
- Clean the Air Filter Regularly: Clean the air filter regularly, especially if you’re cutting in dusty conditions.
- Inspect the Spark Plug Regularly: Inspect the spark plug regularly and replace it if it’s fouled or damaged.
- Store the Saw Properly: Store the saw in a dry place, away from direct sunlight and extreme temperatures.
- Perform Regular Maintenance: Follow the maintenance schedule in your Stihl MS 250 owner’s manual.
Strategic Insights
Beyond the tactical steps, here are some strategic insights I’ve gained over the years:
- Invest in Quality Tools: Don’t skimp on tools. A good spark plug wrench, compression tester, and feeler gauge will make your life much easier.
- Learn Your Saw: Take the time to understand how your Stihl MS 250 works. Read the owner’s manual and familiarize yourself with the different components.
- Keep Records: Keep a record of maintenance tasks, repairs, and fuel mixtures. This will help you track the saw’s performance and identify potential problems early on.
- Join a Community: Connect with other chainsaw users online or in person. Share tips and experiences, and learn from each other.
Next Steps
Now that you’ve learned how to troubleshoot starting problems with your Stihl MS 250, it’s time to put your knowledge into practice.
- Gather Your Tools: Assemble the tools you’ll need, including a spark plug wrench, screwdriver, fuel filter removal tool, compression tester, and feeler gauge.
- Inspect Your Saw: Thoroughly inspect your Stihl MS 250, paying attention to the fuel system, ignition system, air intake, exhaust system, compression, and starter mechanism.
- Follow the Troubleshooting Steps: Use the step-by-step guides in this article to diagnose and resolve any starting problems you encounter.
- Prevent Future Problems: Implement the preventative maintenance tips to keep your Stihl MS 250 running smoothly for years to come.
Conclusion
Troubleshooting starting problems with a Stihl MS 250 can seem daunting, but with a systematic approach and a little patience, you can get your saw back up and running in no time. Remember to prioritize safety, use the right tools, and follow the manufacturer’s recommendations. And don’t be afraid to seek professional help if you’re unsure about any of the steps. With proper care and maintenance, your Stihl MS 250 will be a reliable workhorse for many years to come.
I hope this guide has been helpful. Now get out there and cut some wood! And always remember to wear appropriate safety gear, including eye protection, hearing protection, and gloves. Happy cutting!
