Stihl Saw No Spark Fixes (5 Pro Tips for MS250 Owners)

The global wood processing and firewood industry is experiencing a fascinating shift. On one hand, we see increased automation in large-scale logging operations, with forestry companies leveraging drones for inventory management and harvesters that can fell, delimb, and buck trees in a matter of seconds. On the other hand, there’s a resurgence of interest in traditional woodcraft and sustainable firewood practices, driven by a desire for self-sufficiency and a connection to nature. Did you know that firewood still heats over 12 million homes in the United States alone? And in Europe, demand for sustainably sourced wood pellets for heating is skyrocketing, presenting both opportunities and challenges for small-scale producers.

In this context, reliable equipment is absolutely crucial. That’s why a chainsaw that won’t start can be incredibly frustrating, especially when you’ve got a pile of logs waiting to be processed. I know the feeling. I’ve spent countless hours in the woods, relying on my trusty Stihl MS250 to get the job done. There’s nothing worse than pulling the cord and hearing…nothing. That sinking feeling when you realize you’ve got a “no spark” situation.

That’s why I’ve put together this guide focused specifically on troubleshooting a “no spark” issue on the Stihl MS250. I’ll share some proven tips based on my own experiences and knowledge. Think of this as your personal troubleshooting guide – the one you wish you had before you wasted hours wrestling with a stubborn saw. Let’s dive in.

Stihl Saw No Spark Fixes: 5 Pro Tips for MS250 Owners

The Stihl MS250 is a workhorse, known for its reliability and ease of use. But like any machine, it’s prone to occasional hiccups. One of the most common and frustrating issues is a lack of spark, preventing the engine from firing up. Before you start tearing things apart, remember the golden rule: always disconnect the spark plug wire before doing any work on the ignition system. Safety first!

1. The Spark Plug: The Prime Suspect

The spark plug is the most common culprit in a “no spark” scenario. It’s a relatively inexpensive part, and checking it should be your first step.

Why Spark Plugs Fail:

• Carbon Fouling: This is the most common issue. Carbon deposits build up on the electrode, preventing the spark from jumping the gap. This can happen due to rich fuel mixtures, excessive idling, or using the wrong type of oil.
• Worn Electrode: Over time, the electrode wears down, increasing the gap and making it harder for the spark to jump.
• Cracked or Damaged Insulator: A cracked insulator can allow the spark to ground out, preventing it from reaching the electrode.
• Wet Fouling: If the engine is flooded with fuel, the spark plug can become wet, preventing it from firing.

Step-by-Step Spark Plug Inspection and Replacement:

1. Locate the Spark Plug: On the MS250, the spark plug is typically located under a small cover on the top of the engine, near the cylinder. You’ll need a spark plug wrench or socket to remove it.
2. Remove the Spark Plug: Carefully unscrew the spark plug, being careful not to damage the threads in the cylinder head.
3. Inspect the Spark Plug:
   • Visually Examine: Look for carbon fouling, cracks, or damage to the insulator.
   • Check the Gap: The correct spark plug gap for the MS250 is typically between 0.020 and 0.024 inches (0.5 to 0.6 mm). Use a spark plug gap tool to measure and adjust the gap.
   • Clean the Spark Plug: If the spark plug is only lightly fouled, you can try cleaning it with a wire brush or spark plug cleaner. However, if it’s heavily fouled or damaged, it’s best to replace it.
4. Test for Spark:
   • Reattach the Spark Plug Wire: Connect the spark plug wire to the spark plug.
   • Ground the Spark Plug: Hold the spark plug against the engine block (the metal part). This provides a ground for the spark.
   • Pull the Starter Cord: Pull the starter cord sharply. You should see a bright blue spark jumping across the spark plug gap.
   • No Spark? If you don’t see a spark, the spark plug is likely faulty and needs to be replaced. Even if you do see a spark, if the plug is old or suspect, replacing it is a good idea to rule it out as the issue.
5. Install a New Spark Plug:
   • Use the Correct Spark Plug: Refer to your Stihl MS250 owner’s manual for the correct spark plug type. Using the wrong spark plug can damage the engine. A common replacement is the NGK BPMR7A.
   • Tighten to the Correct Torque: Tighten the spark plug to the torque specification listed in your owner’s manual. Overtightening can damage the cylinder head, and undertightening can cause leaks. Typically, this is around 14-18 Nm (10-13 ft-lbs) for a new spark plug. If reusing a plug, reduce the torque slightly.
6. Test the Saw: Reassemble the saw and try starting it. If the spark plug was the problem, the saw should now start.

Personal Story & Insight:

I once spent an entire afternoon troubleshooting a “no spark” issue, only to discover that the spark plug was the culprit. It looked fine at first glance, but a closer inspection revealed a tiny crack in the insulator. That tiny crack was enough to ground out the spark. From that day on, I always keep a spare spark plug in my toolkit. It’s a cheap and easy way to avoid a lot of frustration.

Data Point: In my experience, replacing the spark plug resolves the “no spark” issue in about 60-70% of cases.

2. The Ignition Coil: The Spark’s Powerhouse

If replacing the spark plug doesn’t solve the problem, the next most likely culprit is the ignition coil. The ignition coil is responsible for generating the high-voltage spark that ignites the fuel-air mixture in the cylinder.

Why Ignition Coils Fail:

• Overheating: Ignition coils can overheat due to prolonged use, especially in hot weather.
• Vibration: Chainsaws are subject to a lot of vibration, which can damage the internal components of the ignition coil.
• Moisture: Moisture can corrode the ignition coil and cause it to short out.
• Air Gap Issues: The air gap between the ignition coil and the flywheel is critical. If the gap is too large or too small, the coil won’t function properly.

Testing the Ignition Coil:

You’ll need a multimeter to test the ignition coil.

1. Disconnect the Spark Plug Wire: Disconnect the spark plug wire from the spark plug.
2. Check Primary Resistance: Set your multimeter to the ohms setting (typically around 200 ohms). Touch one probe to the spark plug wire terminal on the ignition coil and the other probe to the engine ground. You should get a reading, typically between 2-6 ohms. A reading of zero or infinity indicates a faulty coil.
3. Check Secondary Resistance: Set your multimeter to a higher ohms setting (typically around 20,000 ohms). Touch one probe to the spark plug wire terminal on the ignition coil and the other probe to the coil body. You should get a reading, typically between 2,000-4,000 ohms. Again, a reading of zero or infinity indicates a faulty coil.
4. Check for Continuity to Ground: Set your multimeter to the continuity setting (or the lowest ohms setting). Touch one probe to the coil body and the other probe to the engine ground. You should NOT get a reading (open circuit). A reading of continuity indicates a short to ground.

Replacing the Ignition Coil:

1. Disconnect the Old Ignition Coil: Disconnect the spark plug wire and any other wires connected to the ignition coil.
2. Remove the Old Ignition Coil: Unscrew the bolts or screws that hold the ignition coil in place.
3. Install the New Ignition Coil: Install the new ignition coil in the same position as the old one.
4. Set the Air Gap: This is critical! The air gap between the ignition coil and the flywheel must be correct for the ignition coil to function properly. Refer to your Stihl MS250 owner’s manual for the correct air gap specification. Typically, this is around 0.010-0.014 inches (0.25-0.35 mm). You can use a business card or a feeler gauge to set the air gap. Loosen the mounting bolts slightly, insert the business card (or feeler gauge) between the coil and the flywheel magnets, and then tighten the bolts. Remove the card.
5. Reconnect the Wires: Reconnect the spark plug wire and any other wires connected to the ignition coil.
6. Test the Saw: Reassemble the saw and try starting it. If the ignition coil was the problem, the saw should now start.

Personal Story & Insight:

Setting the air gap correctly is crucial. I once replaced an ignition coil and the saw still wouldn’t start. I was ready to throw in the towel, but then I realized I hadn’t set the air gap properly. A quick adjustment, and the saw fired right up. It’s a detail that’s easy to overlook, but it makes all the difference.

Data Point: A faulty ignition coil is responsible for approximately 20-30% of “no spark” issues.

3. The Kill Switch: A Simple Solution Often Overlooked

The kill switch is a simple but important component. Its purpose is to ground out the ignition system, preventing the spark from firing and stopping the engine. A faulty kill switch can sometimes be the cause of a “no spark” issue.

Why Kill Switches Fail:

• Corrosion: The contacts in the kill switch can corrode over time, preventing them from making proper contact.
• Damage: The kill switch can be damaged by impact or wear and tear.
• Wiring Issues: The wires connected to the kill switch can become loose or damaged.

Testing the Kill Switch:

1. Locate the Kill Switch: The kill switch is typically located on the handle of the chainsaw.
2. Disconnect the Kill Switch Wire: Disconnect the wire that runs from the kill switch to the ignition coil. This effectively isolates the kill switch from the ignition system.
3. Test for Spark: Reattach the spark plug wire to the spark plug, ground the spark plug against the engine block, and pull the starter cord. If you now have a spark, the kill switch is likely the problem.
4. Check Continuity: Using a multimeter set to continuity, test the switch in both the “on” and “off” positions. In the “off” position, the switch should have continuity (closed circuit, grounded). In the “on” position, it should NOT have continuity (open circuit).

Replacing the Kill Switch:

1. Remove the Old Kill Switch: Unscrew the bolts or screws that hold the kill switch in place.
2. Disconnect the Wires: Disconnect the wires connected to the old kill switch.
3. Install the New Kill Switch: Install the new kill switch in the same position as the old one.
4. Reconnect the Wires: Reconnect the wires to the new kill switch.
5. Test the Saw: Reassemble the saw and try starting it. If the kill switch was the problem, the saw should now start.

Personal Story & Insight:

I once worked with a logger who was convinced his chainsaw was beyond repair. He’d replaced the spark plug and the ignition coil, but it still wouldn’t start. As a last resort, I checked the kill switch and found that it was stuck in the “off” position. A simple replacement, and the saw was back in action. It just goes to show that sometimes the simplest solutions are the easiest to overlook.

Data Point: A faulty kill switch is responsible for approximately 5-10% of “no spark” issues.

4. The Flywheel: The Rotating Power Source

The flywheel is a critical component of the ignition system. It contains magnets that generate the electrical current needed to power the ignition coil.

Why Flywheels Fail:

• Loose Magnets: The magnets in the flywheel can become loose or damaged, reducing their ability to generate current.
• Rust and Corrosion: Rust and corrosion can build up on the flywheel, interfering with its ability to generate current.
• Damage: The flywheel can be damaged by impact or wear and tear.

Inspecting the Flywheel:

1. Remove the Starter Assembly: You’ll need to remove the starter assembly to access the flywheel.
2. Visually Inspect the Flywheel: Look for loose or damaged magnets, rust, or corrosion.
3. Clean the Flywheel: If the flywheel is rusty or corroded, clean it with a wire brush or sandpaper.
4. Check Magnet Strength: Use a screwdriver to check the strength of the magnets. The screwdriver should be strongly attracted to the magnets. If the magnets are weak, the flywheel may need to be replaced.

Replacing the Flywheel:

This is a more complex repair that may require specialized tools. If you’re not comfortable performing this repair yourself, it’s best to take the chainsaw to a qualified repair technician.

1. Remove the Old Flywheel: Use a flywheel puller to remove the old flywheel.
2. Install the New Flywheel: Install the new flywheel, making sure to align it properly.
3. Tighten the Flywheel Nut: Tighten the flywheel nut to the torque specification listed in your owner’s manual.
4. Reinstall the Starter Assembly: Reinstall the starter assembly.
5. Test the Saw: Reassemble the saw and try starting it. If the flywheel was the problem, the saw should now start.

Personal Story & Insight:

I once had a flywheel that had developed a significant amount of rust due to being stored in a damp shed. While the engine ran, it ran poorly. I was able to clean the rust off with some steel wool and the engine ran like new. Proper storage is important.

Data Point: A faulty flywheel is responsible for approximately 5-10% of “no spark” issues.

5. Wiring and Connections: The Unsung Heroes

Often, the “no spark” issue isn’t due to a faulty component, but rather a simple wiring or connection problem.

Common Wiring and Connection Problems:

• Loose Connections: Wires can become loose over time due to vibration.
• Corroded Connections: Corrosion can build up on the connections, preventing them from making proper contact.
• Damaged Wires: Wires can be damaged by rubbing against other parts of the engine or by being pinched or cut.

Troubleshooting Wiring and Connection Problems:

1. Visually Inspect the Wiring: Look for loose connections, corrosion, or damaged wires.
2. Clean the Connections: Clean any corroded connections with a wire brush or sandpaper.
3. Check for Continuity: Use a multimeter to check for continuity in the wires. If a wire is broken or damaged, it will not have continuity.
4. Repair or Replace Damaged Wires: Repair any damaged wires with electrical tape or replace them with new wires.
5. Secure Loose Connections: Secure any loose connections with wire ties or electrical tape.

Personal Story & Insight:

I once spent hours troubleshooting a “no spark” issue, only to discover that a wire had simply come loose from the ignition coil. A quick reconnection, and the saw was back in action. It’s a good reminder to always check the simple things first.

Data Point: Wiring and connection problems are responsible for approximately 10-15% of “no spark” issues.

Beyond the “No Spark”: Maintaining Your Stihl MS250

While addressing a “no spark” issue is crucial, proactive maintenance is the key to keeping your Stihl MS250 running smoothly for years to come.

Fuel and Oil: The Lifeblood of Your Saw

• Fuel: Always use fresh, high-quality gasoline with an octane rating of 89 or higher. Use a fuel stabilizer if you’re not going to be using the saw for an extended period of time. Ethanol-blended fuels can cause problems, so try to use ethanol-free fuel whenever possible, especially for storage.
• Oil: Use a high-quality two-stroke oil that meets the JASO FD or ISO-L-EGD specifications. Mix the oil with the gasoline at the ratio specified in your owner’s manual (typically 50:1). I always use a pre-measured oil packet to ensure the correct ratio.
• Air Filter: Clean the air filter regularly to prevent dirt and debris from entering the engine. A dirty air filter can restrict airflow, causing the engine to run poorly.
• Fuel Filter: Replace the fuel filter periodically to prevent dirt and debris from clogging the fuel system.
• Chain Sharpness: A sharp chain is essential for efficient cutting. Sharpen the chain regularly using a file or a chain grinder. A dull chain puts unnecessary strain on the engine and can be dangerous.
• Bar and Chain Lubrication: Keep the bar and chain lubricated with a high-quality bar and chain oil. Proper lubrication reduces friction and wear, extending the life of the bar and chain.

Wood Species and Firewood Quality: A Quick Guide

The type of wood you’re cutting can also impact the performance of your chainsaw. Hardwoods like oak, maple, and hickory are denser and require more power to cut than softwoods like pine and fir. When preparing firewood, it’s important to choose wood that is easy to split and burns cleanly.

• Hardwoods: Generally provide more heat per cord and burn longer than softwoods. However, they can be more difficult to split and season.
• Softwoods: Easier to split and season, but burn faster and produce more smoke.

Data Point: Seasoned hardwoods typically have a moisture content of 20% or less, while green hardwoods can have a moisture content of 50% or more.

Chainsaw vs. Axe: A Tool Selection Guide

While a chainsaw is ideal for felling trees and bucking logs, an axe can be a valuable tool for splitting firewood.

• Chainsaw: Best for cutting large quantities of wood quickly and efficiently.
• Axe: Best for splitting firewood, especially hardwoods. A splitting maul is a heavier axe designed specifically for splitting logs.

Case Study: I once worked on a firewood preparation project where we used both a chainsaw and an axe. We used the chainsaw to fell the trees and buck them into logs, and then we used the axe to split the logs into firewood. This combination of tools allowed us to process a large amount of wood quickly and efficiently.

Troubleshooting Guide: Common Problems and Solutions

Here’s a quick troubleshooting guide for some common problems you might encounter with your Stihl MS250:

• Saw Won’t Start:
  • Check the spark plug.
  • Check the ignition coil.
  • Check the kill switch.
  • Check the fuel and air filters.
  • Make sure the fuel is fresh.
• Saw Runs Poorly:
  • Clean the air filter.
  • Replace the fuel filter.
  • Adjust the carburetor.
  • Check the spark plug.
• Saw Smokes Excessively:
  • Use the correct oil mixture.
  • Check the air filter.
  • Adjust the carburetor.
• Saw Overheats:
  • Clean the air filter.
  • Check the cooling fins.
  • Make sure the chain is sharp.

Costs and Budgeting: Planning Your Project

Before starting any wood processing or firewood preparation project, it’s important to consider the costs involved.

• Equipment Costs: Chainsaws, axes, splitting mauls, safety gear, etc.
• Fuel and Oil Costs: Gasoline, two-stroke oil, bar and chain oil.
• Maintenance Costs: Spark plugs, air filters, fuel filters, etc.
• Transportation Costs: Hauling logs and firewood.
• Labor Costs: If you’re hiring someone to help you.

Resource Management Tips:

• Buy in Bulk: Purchase fuel and oil in bulk to save money.
• Maintain Your Equipment: Proper maintenance can extend the life of your equipment and prevent costly repairs.
• Use Recycled Materials: Use recycled pallets or scrap wood to build firewood racks.

Next Steps and Additional Resources

Now that you’ve learned how to troubleshoot a “no spark” issue and maintain your Stihl MS250, you’re well on your way to becoming a wood processing and firewood preparation expert. Here are some additional resources to help you on your journey:

• Stihl Owner’s Manual: The owner’s manual is a valuable resource for information about your chainsaw.
• Online Forums: Online forums are a great place to ask questions and get advice from other chainsaw users.
• Local Repair Shops: If you’re not comfortable performing repairs yourself, take your chainsaw to a qualified repair technician.
• Suppliers of Logging Tools: Baileys, Forestry Suppliers, Northern Tool.
• Drying Equipment Rental Services: Check your local equipment rental companies for firewood kilns or dehumidifiers.

So, there you have it. With a little knowledge and some elbow grease, you can keep your Stihl MS250 running like a champ for years to come. Now get out there and make some sawdust! Remember to always prioritize safety and enjoy the satisfying feeling of transforming raw wood into a useful resource. And if you ever find yourself scratching your head over a “no spark” issue, just remember these tips and you’ll be back in the woods in no time.

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