No Spark On Stihl Chainsaw (5 Expert Fixes For MS250 Ignition)

About 80% of chainsaw owners will experience an ignition problem at some point in their chainsaw’s lifespan. When your Stihl MS250 chainsaw refuses to roar to life, and you suspect the spark is missing, it can be incredibly frustrating. It feels like your work is grinding to a halt. I’ve been there countless times myself, wrestling with stubborn engines in the heart of the woods. Over the years, I’ve learned to troubleshoot and fix these issues, often relying on simple tools and a bit of ingenuity. The Stihl MS250 is a workhorse, but even the best machines can suffer from ignition problems. This article will walk you through five expert fixes to get that spark back, drawing on my experience and expertise to help you diagnose and resolve the issue efficiently.

No Spark on Stihl Chainsaw: 5 Expert Fixes for MS250 Ignition

1. Understanding the Ignition System

Before diving into the fixes, it’s crucial to understand how the ignition system of your Stihl MS250 works. The ignition system is responsible for creating the spark that ignites the fuel-air mixture in the cylinder, starting the engine. This system typically consists of the following components:

Spark Plug: The component that delivers the electrical spark into the combustion chamber.
Ignition Coil: Generates the high-voltage electricity needed for the spark.
Flywheel: Contains magnets that induce a current in the ignition coil as it rotates.
Ignition Module (or Electronic Ignition): Controls the timing and delivery of the spark.
Wiring and Connections: Connect all the components and allow the electrical current to flow.

When any of these components fail or are compromised, it can lead to a no-spark condition.

2. Fix #1: Spark Plug Inspection and Replacement

The spark plug is often the first suspect when dealing with a no-spark issue. Here’s how to inspect and, if necessary, replace it:

Inspection

Remove the Spark Plug: Use a spark plug wrench to carefully remove the spark plug from the cylinder head.
Visual Check: Examine the spark plug for signs of damage, such as cracks, chips, or excessive wear. Also, look for fouling—deposits of carbon or oil on the electrode.
Electrode Condition: The electrode should be clean and have a sharp edge. A rounded or heavily worn electrode indicates that the spark plug needs replacement.
Gap Check: Use a spark plug gap tool to ensure the gap between the center and ground electrodes is within the specified range for the Stihl MS250 (typically 0.5mm or 0.02 inches). Adjust the gap if necessary.

Replacement

If the spark plug is damaged, heavily fouled, or the electrode is worn, replace it with a new spark plug of the correct type for your Stihl MS250. Here’s the process:

Choose the Right Spark Plug: Consult your Stihl MS250 owner’s manual to determine the correct spark plug type. Using the wrong spark plug can damage your engine.
Install the New Spark Plug: Carefully thread the new spark plug into the cylinder head by hand to avoid cross-threading. Once it’s snug, tighten it with a spark plug wrench to the torque specified in the owner’s manual.
Test for Spark: With the new spark plug installed, reattach the spark plug wire and test for spark by grounding the spark plug against the engine block while pulling the starter cord. You should see a strong, blue spark.

Personal Experience: I once spent an entire afternoon troubleshooting a chainsaw that wouldn’t start, only to discover that the spark plug was the culprit. It looked fine at first glance, but upon closer inspection, I noticed a hairline crack in the ceramic insulator. A new spark plug solved the problem instantly.

3. Fix #2: Checking the Spark Plug Wire and Boot

The spark plug wire and boot connect the ignition coil to the spark plug, delivering the high-voltage electricity needed for ignition. Problems with the wire or boot can interrupt the flow of electricity and prevent the engine from starting.

Inspection

Visual Inspection: Examine the spark plug wire for any signs of damage, such as cracks, cuts, or fraying. Also, check the boot for cracks, tears, or looseness.
Continuity Test: Use a multimeter to test the continuity of the spark plug wire. Disconnect the wire from both the spark plug and the ignition coil. Set the multimeter to the continuity setting and touch one probe to each end of the wire. The multimeter should indicate continuity (a low resistance reading). If there’s no continuity, the wire is broken and needs replacement.
Boot Connection: Ensure the boot is securely attached to both the spark plug and the spark plug wire. A loose connection can cause a weak or intermittent spark.

Replacement

If the spark plug wire or boot is damaged or shows no continuity, replace it with a new one. Here’s how:

Disconnect the Old Wire: Disconnect the old spark plug wire from both the spark plug and the ignition coil.
Install the New Wire: Attach the new spark plug wire to the ignition coil and the spark plug, ensuring a secure connection at both ends.
Test for Spark: Test for spark by grounding the spark plug against the engine block while pulling the starter cord. You should see a strong, blue spark.

Pro Tip: When replacing the spark plug wire, use dielectric grease on the inside of the boot to help prevent moisture from entering and causing corrosion.

4. Fix #3: Inspecting and Cleaning the Flywheel and Ignition Coil

The flywheel and ignition coil work together to generate the high-voltage electricity needed for the spark. The flywheel contains magnets that induce a current in the ignition coil as it rotates. If the flywheel or ignition coil is dirty, damaged, or improperly gapped, it can cause a no-spark condition.

Inspection

Remove the Flywheel Cover: Remove the flywheel cover to access the flywheel and ignition coil.
Visual Inspection: Examine the flywheel for any signs of damage, such as cracks, chips, or rust. Also, check the ignition coil for cracks, burns, or other damage.
Cleaning: Clean the flywheel and ignition coil with a wire brush or sandpaper to remove any rust, dirt, or debris. Pay particular attention to the magnets on the flywheel and the laminations on the ignition coil.
Air Gap: Check the air gap between the flywheel and the ignition coil. This gap should be within the range specified in the Stihl MS250 owner’s manual (typically 0.3mm or 0.012 inches). Use a feeler gauge to measure the gap and adjust it if necessary. To adjust the gap, loosen the screws holding the ignition coil in place, insert the feeler gauge between the flywheel and the ignition coil, and tighten the screws.
Wiring: Trace the wires leading to the ignition coil and check for any breaks.

Testing the Ignition Coil

You can use a multimeter to test the primary and secondary resistance of the ignition coil.

Primary Resistance: Set the multimeter to the ohms setting and measure the resistance between the primary terminals of the ignition coil. The resistance should be within the range specified in the Stihl MS250 service manual.
Secondary Resistance: Measure the resistance between the spark plug wire terminal and one of the primary terminals. Again, compare the reading to the specifications in the service manual.

If the resistance readings are outside the specified range, the ignition coil is likely faulty and needs to be replaced.

Replacement

If the flywheel or ignition coil is damaged or the air gap is incorrect, replace it with a new one. Here’s how:

Remove the Old Components: Remove the old flywheel and ignition coil.
Install the New Components: Install the new flywheel and ignition coil, ensuring the air gap is properly adjusted.
Test for Spark: Test for spark by grounding the spark plug against the engine block while pulling the starter cord. You should see a strong, blue spark.

Field Story: I remember once working on a logging site where the MS250’s flywheel had accumulated so much sawdust and grime that it was interfering with the magnetic field. After a thorough cleaning and re-gapping, the chainsaw fired right up. Regular maintenance can prevent these issues.

5. Fix #4: Checking the Kill Switch and Wiring

The kill switch is designed to ground the ignition system, stopping the engine. If the kill switch or its wiring is faulty, it can ground the ignition system even when the switch is in the “run” position, preventing the engine from starting.

Inspection

Visual Inspection: Examine the kill switch and its wiring for any signs of damage, such as cracks, breaks, or loose connections.
Continuity Test: Disconnect the kill switch from the ignition system. Set the multimeter to the continuity setting and touch one probe to each terminal of the kill switch. With the switch in the “run” position, the multimeter should not indicate continuity (an open circuit). With the switch in the “stop” position, the multimeter should indicate continuity (a closed circuit). If the kill switch does not function as described, it is faulty and needs to be replaced.
Wiring Check: Check the wiring from the kill switch to the ignition module for shorts to the chassis.

Replacement

If the kill switch is faulty, replace it with a new one. Here’s how:

Disconnect the Old Switch: Disconnect the old kill switch from the ignition system.
Install the New Switch: Connect the new kill switch to the ignition system, ensuring a secure connection.
Test for Spark: Test for spark by grounding the spark plug against the engine block while pulling the starter cord. You should see a strong, blue spark.

Practical Tip: Sometimes, the kill switch wire can become frayed and intermittently ground against the engine block. Carefully inspect the wire and repair any damaged sections with electrical tape or replace the wire entirely.

6. Fix #5: Inspecting the Ignition Module

The ignition module is the brain of the ignition system, controlling the timing and delivery of the spark. If the ignition module is faulty, it can prevent the engine from starting. Although less common than spark plug or wiring issues, ignition module failure can occur, particularly in older chainsaws.

Inspection

Visual Inspection: Examine the ignition module for any signs of damage, such as cracks, burns, or melted components.
Testing: Testing an ignition module typically requires specialized equipment, such as a spark tester or an oscilloscope. However, you can perform a basic test using a multimeter to check the continuity of the wiring and the resistance of the module. Consult the Stihl MS250 service manual for specific testing procedures and resistance values.
Voltage Test: With the chainsaw assembled, you can use a multimeter to check if the ignition module is receiving power from the flywheel. Set the multimeter to measure AC voltage and connect the probes to the ignition module’s input terminals. Pull the starter cord and observe the voltage reading. If there is no voltage, the flywheel or the wiring between the flywheel and the ignition module may be faulty.

Replacement

If the ignition module is faulty, replace it with a new one. Here’s how:

Remove the Old Module: Disconnect the old ignition module from the engine.
Install the New Module: Connect the new ignition module to the engine, ensuring a secure connection.
Test for Spark: Test for spark by grounding the spark plug against the engine block while pulling the starter cord. You should see a strong, blue spark.

Real-World Example: I once worked on a Stihl MS250 that would only start intermittently. After checking all the usual suspects (spark plug, wiring, etc.), I finally suspected the ignition module. A replacement module solved the problem and restored the chainsaw to reliable operation.

Wood Anatomy and Properties: Their Impact on Chainsaw Performance

Understanding wood anatomy and properties is crucial for efficient chainsaw operation and maintenance. The type of wood you’re cutting directly affects the wear and tear on your chainsaw, the chain’s sharpness, and the overall cutting performance.

Hardwood vs. Softwood

Hardwoods: Generally denser and more durable, hardwoods like oak, maple, and hickory can dull chainsaw chains more quickly. Their tighter grain structure requires more force to cut through, increasing the load on the engine.
Softwoods: Softwoods like pine, fir, and spruce are less dense and easier to cut. However, they tend to be resinous, which can cause buildup on the chain and bar, requiring more frequent cleaning.

Data Point: Hardwoods typically have a density ranging from 500 to 1000 kg/m³, while softwoods range from 300 to 700 kg/m³. This difference in density directly affects the cutting resistance and the power required from the chainsaw.

Moisture Content

Green Wood: Freshly cut wood has a high moisture content, which can make it more difficult to cut. The moisture increases friction between the chain and the wood, slowing down the cutting process.
Dry Wood: Seasoned wood with lower moisture content is generally easier to cut. However, extremely dry wood can be brittle and prone to splintering, which can be hazardous.

Wood Science Insight: The ideal moisture content for cutting firewood is between 20% and 30%. This range provides a balance between ease of cutting and reduced splintering.

Grain Structure

The grain pattern of the wood also affects cutting. Straight-grained wood is easier to cut than wood with knots or irregular grain patterns. Knots are particularly challenging as they are denser and can deflect the chain, increasing the risk of kickback.

Logging Tool Selection and Maintenance Best Practices

Choosing the right logging tools and maintaining them properly is essential for safety and efficiency. Here are some best practices:

Chainsaw Selection

Size and Power: Select a chainsaw that is appropriate for the size of the trees you’ll be cutting. The Stihl MS250 is a versatile option for small to medium-sized trees.
Bar Length: Choose a bar length that is slightly longer than the diameter of the trees you’ll be cutting. This ensures that you can make clean cuts without overextending the chainsaw.

Chainsaw Maintenance

Chain Sharpening: Sharpen the chain regularly to maintain optimal cutting performance. A dull chain requires more force to cut, increasing the risk of kickback and engine strain.
Chain Tension: Check the chain tension before each use and adjust as needed. A loose chain can derail and cause injury, while an overtight chain can damage the bar and sprocket.
Bar Lubrication: Ensure the bar oil reservoir is full and that the oiler is functioning properly. Proper lubrication reduces friction and wear on the bar and chain, extending their lifespan.
Air Filter Cleaning: Clean the air filter regularly to prevent dust and debris from entering the engine. A clogged air filter can reduce engine power and increase fuel consumption.
Fuel Mixture: Use the correct fuel mixture (typically a 50:1 ratio of gasoline to two-stroke oil) to ensure proper engine lubrication and performance.

Other Essential Logging Tools

Felling Axe or Wedge: Use a felling axe or wedge to help direct the fall of the tree and prevent it from pinching the chainsaw bar.
Cant Hook or Peavey: Use a cant hook or peavey to roll logs and position them for cutting.
Measuring Tape: Use a measuring tape to accurately measure logs for firewood or timber.
Safety Gear: Always wear appropriate safety gear, including a helmet, eye protection, hearing protection, gloves, and chainsaw chaps.

Firewood Seasoning Techniques and Safety Considerations

Properly seasoning firewood is crucial for efficient burning and reducing creosote buildup in your chimney. Here are some techniques and safety considerations:

Seasoning Techniques

Stacking: Stack firewood in a single row with gaps between the logs to allow for air circulation.
Elevation: Elevate the firewood off the ground using pallets or boards to prevent moisture from wicking up from the soil.
Sun and Wind Exposure: Position the firewood pile in a sunny and windy location to promote drying.
Covering: Cover the top of the firewood pile with a tarp or roof to protect it from rain and snow. However, leave the sides open to allow for air circulation.

Firewood Seasoning Data: Firewood typically takes 6 to 12 months to season properly, depending on the type of wood and the climate. The moisture content should be below 20% for optimal burning.

Safety Considerations

Stacking Stability: Stack firewood in a stable manner to prevent it from collapsing.
Pest Control: Be aware of potential pests, such as insects and rodents, that may infest firewood. Store firewood away from your house to prevent them from entering your home.
Fire Safety: Keep firewood away from heat sources and open flames to prevent fire hazards.

Firewood Value Ratings

Different types of firewood have different heat values, measured in British Thermal Units (BTUs) per cord. Here are some examples:

Oak: High heat value (approximately 24 million BTUs per cord)
Maple: Medium heat value (approximately 20 million BTUs per cord)
Pine: Low heat value (approximately 15 million BTUs per cord)

Project Planning and Execution: A Case Study

Let’s consider a case study of a firewood preparation project to illustrate the practical application of the concepts discussed above.

Project Overview

A homeowner wants to prepare 5 cords of firewood for the upcoming winter. The wood source is a mix of oak and maple trees that were recently felled on their property.

Project Planning

Assessment: Assess the amount of wood available and determine the necessary equipment and tools.
Safety Plan: Develop a safety plan that includes wearing appropriate safety gear, establishing a safe work zone, and practicing safe chainsaw operation techniques.
Cutting Plan: Plan the cutting process to maximize efficiency and minimize waste. Cut the logs into manageable lengths (typically 16-18 inches).
Splitting Plan: Plan the splitting process to split the logs into appropriate sizes for the wood stove or fireplace.
Stacking Plan: Plan the stacking process to stack the firewood in a stable and well-ventilated manner.

Project Execution

Felling: If necessary, fell the trees safely using proper felling techniques and equipment.
Bucking: Cut the logs into manageable lengths using a chainsaw.
Splitting: Split the logs using a manual or hydraulic splitter.
Stacking: Stack the firewood in a single row with gaps between the logs, elevating it off the ground, and covering the top with a tarp.
Seasoning: Allow the firewood to season for 6 to 12 months before burning.

Cost-Benefit Analysis

Equipment Costs: Chainsaw, splitter, safety gear, etc.
Labor Costs: Time spent felling, bucking, splitting, and stacking.
Fuel Costs: Gasoline and bar oil for the chainsaw.
Benefits: Savings on heating costs, exercise, and satisfaction of self-sufficiency.

By carefully planning and executing the firewood preparation project, the homeowner can efficiently and safely prepare a sustainable source of heat for the winter.

Conclusion: Key Takeaways and Next Steps

Troubleshooting a Stihl MS250 with no spark can be a daunting task, but by following these five expert fixes, you can systematically diagnose and resolve the issue. Remember to start with the simplest solutions, such as checking the spark plug and wiring, before moving on to more complex components like the ignition coil and module. Regular maintenance, including cleaning the flywheel and adjusting the air gap, can prevent many ignition problems.

Key Takeaways:

A strong, blue spark is essential for starting the engine.
A faulty spark plug is often the culprit behind a no-spark condition.
Damaged wiring or a faulty kill switch can ground the ignition system.
A dirty or improperly gapped flywheel and ignition coil can prevent the engine from starting.
A faulty ignition module can disrupt the timing and delivery of the spark.

Next Steps:

Gather the necessary tools and equipment.
Follow the troubleshooting steps outlined in this article.
Consult the Stihl MS250 service manual for specific testing procedures and specifications.
If you’re not comfortable performing the repairs yourself, take the chainsaw to a qualified service technician.

By taking these steps, you can get your Stihl MS250 back up and running, allowing you to continue your wood processing projects with confidence.