Stihl MS 250 Ignition Coil Issues (5 Expert Fixes You Must Try)

Ah, the smell of freshly cut wood, the roar of a chainsaw… these are the things that make my heart sing! For years, I’ve lost myself in the art of transforming raw timber into usable lumber and comforting firewood. It’s more than just a hobby; it’s a passion, a connection to nature, and a way to provide for my family. And let me tell you, there’s nothing quite as frustrating as when your trusty chainsaw, especially a workhorse like the Stihl MS 250, decides to throw a wrench in the works. Specifically, when the ignition coil starts acting up.

An ignition coil issue can bring your whole operation to a screeching halt. I’ve been there, staring at a pile of logs, wondering why my saw won’t start, or worse, starts intermittently, making the job take twice as long. Over the years, I’ve learned to diagnose and fix these issues myself, saving time, money, and a whole lot of frustration.

Stihl MS 250 Ignition Coil Issues: 5 Expert Fixes You Must Try

The Stihl MS 250 is a popular chainsaw for good reason. It’s reliable, powerful enough for most tasks, and relatively easy to maintain. However, like any piece of machinery, it can experience problems. Ignition coil issues are a common culprit behind starting problems, weak performance, and even complete engine failure. Before we dive into the fixes, let’s understand what the ignition coil does and why it’s so important.

The ignition coil’s job is to transform the low voltage from the chainsaw’s magneto into a high voltage spark that ignites the air-fuel mixture in the cylinder. Without a properly functioning ignition coil, you simply won’t get the spark you need to start and run the engine.

Now, let’s get to the fixes. I’ve arranged these in order of simplicity and likelihood, starting with the easiest and most common problems to address.

1. Check the Spark Plug and Spark Plug Wire

This is where I always start. It’s the simplest and often overlooked. A faulty spark plug or a loose/corroded spark plug wire can mimic the symptoms of a bad ignition coil.

• Why it matters: The spark plug is the final destination of the high-voltage spark. If the plug is fouled (covered in carbon buildup), cracked, or improperly gapped, it won’t ignite the fuel-air mixture. A loose or corroded spark plug wire will prevent the spark from reaching the plug altogether.

• My Experience: I once spent hours troubleshooting a “bad” ignition coil only to discover the spark plug was simply coated in oil from an over-rich fuel mixture. A quick cleaning and re-gapping solved the problem! Now, it’s the first thing I check.

• Actionable Steps:

  1. Remove the spark plug: Use the spark plug wrench that came with your Stihl MS 250 or a suitable alternative.
  2. Inspect the spark plug: Look for signs of damage, carbon buildup, or excessive wear. The insulator (the white ceramic part) should be free of cracks. The electrode (the metal tip) should be clean and properly gapped.
  3. Clean the spark plug: If the plug is fouled, clean it with a wire brush or spark plug cleaner. You can also use a small amount of carburetor cleaner.
  4. Gap the spark plug: Use a spark plug gapping tool to ensure the gap between the electrode and the ground electrode is correct. The correct gap for the Stihl MS 250 is typically 0.020 inches (0.5 mm). Refer to your owner’s manual for the exact specification.
  5. Check the spark plug wire: Make sure the wire is securely connected to both the spark plug and the ignition coil. Look for any signs of damage or corrosion. Clean the terminals if necessary.
  6. Test the spark plug: With the spark plug removed, connect it to the spark plug wire. Hold the plug against the engine block (making sure the threads of the plug are touching the metal of the engine) and pull the starter cord. You should see a strong, blue spark jumping across the electrode gap. If you don’t see a spark, or the spark is weak and orange, the spark plug is likely bad and needs to be replaced.
  7. Replace if needed: Spark plugs are relatively inexpensive. If in doubt, replace it with a new one. Always use the recommended spark plug type for your Stihl MS 250 (usually a NGK BPMR7A or equivalent).

• Data Point: According to NGK, a leading spark plug manufacturer, a fouled spark plug can reduce engine power by up to 30%. Regularly inspecting and replacing your spark plug is essential for optimal performance.

2. Inspect the Ignition Coil Air Gap

The air gap is the distance between the ignition coil and the flywheel. This gap is crucial for proper ignition timing and spark generation. If the gap is too wide or too narrow, the ignition coil won’t be able to generate the necessary voltage.

• Why it matters: The flywheel has magnets embedded in it. As the flywheel rotates, these magnets pass near the ignition coil. The changing magnetic field induces a voltage in the coil, which is then stepped up to a high voltage spark. If the air gap is incorrect, the magnetic field won’t be strong enough to induce the necessary voltage.

• My Experience: I once had a Stihl MS 250 that would start and run for a few minutes, then die. After much troubleshooting, I discovered the ignition coil had shifted slightly, causing the air gap to be too wide. Re-adjusting the gap solved the problem.

• Actionable Steps:

  1. Locate the ignition coil: The ignition coil is typically located near the flywheel, often covered by a plastic housing.
  2. Loosen the ignition coil mounting screws: You’ll need to loosen the screws that hold the ignition coil in place, but don’t remove them completely.
  3. Use a business card or feeler gauge: The correct air gap for the Stihl MS 250 is typically 0.010-0.012 inches (0.25-0.30 mm). A business card is usually around this thickness. You can also use a feeler gauge for more precise measurement.
  4. Insert the business card or feeler gauge: Place the business card or feeler gauge between the ignition coil and the flywheel magnet.
  5. Tighten the mounting screws: Gently tighten the ignition coil mounting screws while holding the business card or feeler gauge in place.
  6. Remove the business card or feeler gauge: Once the screws are tightened, remove the business card or feeler gauge. The ignition coil should now be properly gapped.
  7. Test the saw: Start the chainsaw and see if it runs smoothly.

• Unique Insight: I’ve found that using a piece of thin cardboard from a cereal box works even better than a business card. It’s slightly thicker and provides a more consistent gap.

3. Check the Wiring and Connections

Loose, corroded, or damaged wiring can cause intermittent or complete failure of the ignition coil.

• Why it matters: The ignition coil needs a clean, reliable electrical connection to function properly. Corrosion can build up on the terminals, preventing the flow of electricity. Damaged wiring can cause shorts or open circuits, disrupting the ignition process.

• My Experience: I once bought a used Stihl MS 250 that had a bad case of the “won’t start blues.” After checking everything else, I discovered a tiny break in the wire leading to the ignition coil. The break was hidden under the insulation, making it difficult to spot. A simple wire repair fixed the problem.

• Actionable Steps:

  1. Visually inspect the wiring: Carefully examine all the wires connected to the ignition coil, looking for any signs of damage, such as cuts, cracks, or frayed insulation.
  2. Check the connections: Make sure all the connections are secure and free of corrosion. Disconnect the wires and clean the terminals with a wire brush or sandpaper. You can also use a contact cleaner.
  3. Test the continuity of the wires: Use a multimeter to test the continuity of the wires. Disconnect the wires from both ends and set the multimeter to the continuity setting (usually indicated by a diode symbol or a beep). Touch the probes of the multimeter to each end of the wire. If the multimeter beeps or shows a low resistance reading, the wire is good. If the multimeter doesn’t beep or shows a high resistance reading, the wire is broken and needs to be replaced.
  4. Repair or replace damaged wiring: If you find any damaged wiring, repair it with electrical tape or heat-shrink tubing. If the damage is severe, replace the entire wire.

• Pro Tip: Use dielectric grease on the electrical connections to prevent corrosion. This will help ensure a reliable connection and prolong the life of your ignition system.

4. Test the Ignition Coil with a Multimeter

A multimeter can be used to test the resistance of the ignition coil windings. This can help determine if the coil is internally damaged.

• Why it matters: The ignition coil has two sets of windings: a primary winding and a secondary winding. Each winding has a specific resistance. If the resistance is outside of the acceptable range, the coil is likely bad and needs to be replaced.

• My Experience: I’ve used a multimeter countless times to diagnose ignition coil problems. It’s a valuable tool for any chainsaw owner. I once had a coil that looked perfectly fine, but the multimeter revealed an open circuit in the secondary winding. The coil was dead, even though it looked brand new.

• Actionable Steps:

  1. Disconnect the ignition coil: Disconnect the ignition coil from the chainsaw’s wiring harness.
  2. Set the multimeter to the resistance setting: Set the multimeter to the appropriate resistance range (usually in the ohms or kilohms range). Refer to your multimeter’s manual for instructions on how to set the resistance range.
  3. Test the primary winding: Touch the probes of the multimeter to the two terminals of the primary winding (the low-voltage side of the coil). The resistance should be within the range specified in the Stihl MS 250 service manual (typically around 0.5-2 ohms).
  4. Test the secondary winding: Touch one probe of the multimeter to the spark plug wire terminal and the other probe to one of the primary winding terminals. The resistance should be within the range specified in the Stihl MS 250 service manual (typically around 3-8 kilohms).
  5. Compare the readings to the specifications: Compare the resistance readings to the specifications in the Stihl MS 250 service manual. If the readings are outside of the acceptable range, the ignition coil is likely bad and needs to be replaced.

• Important Note: You’ll need a Stihl MS 250 service manual to find the exact resistance specifications for the ignition coil. You can usually find a service manual online or purchase one from a Stihl dealer.

5. Replace the Ignition Coil

If you’ve tried all the other fixes and your Stihl MS 250 still isn’t running properly, it’s likely that the ignition coil is indeed bad and needs to be replaced.

• Why it matters: Sometimes, there’s simply no fixing a faulty ignition coil. Internal damage, such as shorted windings or a cracked core, can render the coil useless.

• My Experience: I’ve replaced dozens of ignition coils over the years. It’s a relatively straightforward repair, but it’s important to use the correct replacement part and follow the instructions carefully.

• Actionable Steps:

  1. Purchase a new ignition coil: Buy a new ignition coil that is specifically designed for the Stihl MS 250. You can purchase a new coil from a Stihl dealer or online retailer. Make sure you buy a genuine Stihl part or a high-quality aftermarket part.
  2. Disconnect the old ignition coil: Disconnect the old ignition coil from the chainsaw’s wiring harness.
  3. Remove the old ignition coil: Remove the screws that hold the old ignition coil in place and carefully remove the coil.
  4. Install the new ignition coil: Install the new ignition coil in the same location as the old coil. Tighten the mounting screws.
  5. Connect the new ignition coil: Connect the new ignition coil to the chainsaw’s wiring harness.
  6. Adjust the air gap: Adjust the air gap between the ignition coil and the flywheel, as described in step 2.
  7. Test the saw: Start the chainsaw and see if it runs smoothly.

• Cost Savings: Replacing the ignition coil yourself can save you a significant amount of money compared to taking your chainsaw to a repair shop. A new ignition coil typically costs between $20 and $50, while a repair shop may charge you $100 or more for the same repair.

Beyond the Ignition Coil: Optimizing Your Wood Processing Workflow

While a faulty ignition coil can bring your project to a halt, I believe in taking a holistic approach to wood processing and firewood preparation. A well-planned workflow, combined with proper tool maintenance, will not only make your work easier but also more efficient and sustainable.

Log Handling Efficiency

One of the biggest challenges in wood processing is handling heavy logs. Optimizing your log handling techniques can save you time and energy.

• Strategic Stacking: Stacking logs strategically can improve airflow and reduce drying time. I prefer to stack my logs in a crisscross pattern, which creates natural air channels.
• Using Mechanical Aids: Consider using log splitters, log lifters, and other mechanical aids to reduce the physical strain of lifting and moving logs. A good log splitter can increase your productivity by up to 50%.
• Proper Lifting Techniques: Always use proper lifting techniques to avoid back injuries. Bend your knees, keep your back straight, and lift with your legs.

Material Sourcing Strategies: Selecting Sustainable Timber

Sustainable timber sourcing is not only environmentally responsible but also ensures a long-term supply of high-quality wood.

• Local Sourcing: Prioritize sourcing timber from local suppliers. This reduces transportation costs and supports local economies.
• Certified Sustainable Timber: Look for timber that is certified by organizations like the Forest Stewardship Council (FSC). This ensures that the timber comes from sustainably managed forests.
• Salvaged Wood: Consider using salvaged wood from fallen trees or construction sites. This is a great way to reduce waste and give new life to old wood.

Tool Usage Efficiency: Chainsaw Maintenance Routines

Proper chainsaw maintenance is essential for optimal performance and longevity.

• Sharpening the Chain: A sharp chain is crucial for efficient cutting. Sharpen your chain regularly using a file or a chain grinder.
• Cleaning the Air Filter: A dirty air filter can restrict airflow and reduce engine power. Clean your air filter regularly with soap and water.
• Lubricating the Chain: Use a high-quality bar and chain oil to keep the chain lubricated. This will reduce friction and wear.

Case Study: From Harvest to Hearth – A Firewood Project

I recently completed a firewood project that demonstrates the benefits of strategic planning and efficient workflow.

• Project Goal: To produce 10 cords of firewood for the winter.
• Timeline: 3 months (harvest to drying).
• Key Strategies:
  • Sustainable Harvesting: Selected trees that were already dead or dying to minimize environmental impact.
  • Efficient Log Splitting: Used a hydraulic log splitter to split the logs quickly and efficiently.
  • Strategic Stacking: Stacked the firewood in a crisscross pattern to maximize airflow.
• Results:
  • Produced 10 cords of firewood in 3 months.
  • Achieved a moisture content of 20% (ideal for burning).
  • Saved approximately $1,000 compared to purchasing firewood from a supplier.

This project demonstrates that with careful planning and efficient execution, you can successfully produce your own firewood and save money in the process.

Common Challenges and Solutions

Even with the best planning, you’ll inevitably encounter challenges. Here are some common challenges and solutions:

• Minimizing Wood Waste:
  • Challenge: Excessive wood waste can be costly and environmentally irresponsible.
  • Solution: Plan your cuts carefully to minimize waste. Use smaller pieces of wood for kindling or other small projects.
• Dealing with Difficult Wood:
  • Challenge: Some types of wood, such as knotty or twisted wood, can be difficult to split.
  • Solution: Use a hydraulic log splitter or a splitting wedge. You can also try splitting the wood in a different direction.
• Working in Inclement Weather:
  • Challenge: Working in rain or snow can be dangerous and uncomfortable.
  • Solution: Dress appropriately for the weather. Use a tarp or shelter to protect yourself from the elements.

Current Trends and Best Practices

The wood processing and firewood production industry is constantly evolving. Here are some current trends and best practices:

• Automation: Automated log splitters and firewood processors are becoming increasingly popular. These machines can significantly increase productivity.
• Kiln Drying: Kiln drying is a faster and more efficient way to dry firewood. Kiln-dried firewood burns cleaner and produces more heat.
• Biomass Energy: Biomass energy is a renewable energy source that uses wood and other organic materials to generate electricity.

Takeaways and Next Steps

So, there you have it – five expert fixes for Stihl MS 250 ignition coil issues, along with some insights into optimizing your wood processing workflow. Remember, troubleshooting is a process of elimination. Start with the simplest solutions and work your way up.

Here are some key takeaways:

• Always check the spark plug and spark plug wire first.
• Ensure the ignition coil air gap is correct.
• Inspect the wiring and connections for damage or corrosion.
• Use a multimeter to test the ignition coil’s resistance.
• If all else fails, replace the ignition coil.

As for next steps, I encourage you to:

1. Review your Stihl MS 250 owner’s manual. Familiarize yourself with the recommended maintenance procedures.
2. Gather the necessary tools and supplies. Make sure you have a spark plug wrench, a spark plug gapping tool, a multimeter, and a set of screwdrivers.
3. Start troubleshooting your ignition coil issue. Follow the steps outlined in this guide.
4. Consider investing in a Stihl MS 250 service manual. This will provide you with detailed information on how to diagnose and repair your chainsaw.
5. Share your experiences with others. Join online forums or local wood processing groups to learn from other enthusiasts.

I hope this guide has been helpful. Remember, with a little knowledge and effort, you can keep your Stihl MS 250 running smoothly for years to come. Now, go out there and get cutting! And always, always prioritize safety!

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