Dealing with a Stihl MS 250 that refuses to start because of a lack of spark can be incredibly frustrating, especially when you are eager to tackle yard work. This specific issue cuts across all user levels, from the weekend homeowner to the seasoned professional, effectively halting any progress. Understanding the intricate relationship between the ignition coil, spark plug, and the entire fuel system is the first step toward a reliable solution. This guide moves beyond simple troubleshooting to provide a deep dive into the root causes and effective fixes for the no-spark scenario.
Decoding the Ignition System of the MS 250
The ignition system in your Stihl MS 250 is a precise sequence that must occur for the engine to run. It begins with the ignition switch, travels to the ignition coil, and culminates in a spark at the spark plug gap. If any component in this chain fails, the result is a silent engine or one that cranks without firing. Diagnosing the problem requires a systematic approach to isolate whether the issue is electrical or mechanical in nature.
Common Culprits: Spark Plug and Wire Inspection
The spark plug is often the first suspect when facing a no-spark condition. Over time, the electrode wears down, the porcelain insulator cracks, or carbon buildup prevents a proper spark. Similarly, the spark arrestor, a small mesh screen integrated into the plug, can become clogged, disrupting the ignition process. You should also examine the high-tension wire; cracks in the boot or damage to the coil of wire inside can leak the electrical charge before it reaches the plug.
Remove the spark plug and inspect the electrode for excessive gap or damage.
Check the high-tension wire for cracks or moisture intrusion.
Clean or replace the spark arrestor mesh if it is heavily fouled.
Verify that the plug is properly gapped according to the MS 250 specifications.
Beyond the Spark: The Role of the Ignition Coil
If the spark plug and wire check out, the ignition coil becomes the primary focus. This component is responsible for amplifying the battery voltage to the thousands of volts required to create a spark. A failing coil often shows no external signs but will test poorly with a multimeter. Environmental factors, such as extreme heat or physical impact from kickback, can cause internal windings to short out, breaking the circuit necessary for spark generation.
Testing Electrical Components
Using a multimeter is the most accurate way to determine if the ignition coil is functioning correctly. You will need to test the resistance across the primary and secondary coils. Resistance that is too high indicates a break in the winding, while resistance too low suggests a short circuit. Comparing your readings to the manufacturer’s specifications for the Stihl MS 250 is crucial for a definitive diagnosis.
Set your multimeter to the Ohms setting.
Disconnect the wiring harness from the ignition coil.
Touch the probes to the terminals and record the resistance reading.
Compare the results to the service manual values to confirm coil health.
Fuel System Factors Contributing to Ignition Failure
While it might seem counterintuitive, fuel system issues can sometimes manifest as an ignition problem. A flooded engine, caused by too much fuel in the cylinder, can prevent the spark from igniting the air/fuel mixture. Additionally, old or contaminated fuel creates a weak burn that fails to sustain combustion, which can be misinterpreted as a lack of spark during the initial pull.
