Stihl MS250 Coil Adjustment (5 Pro Tips for Perfect Timing)
The Stihl MS250 is a workhorse, a reliable companion for countless homeowners and professionals tackling everything from limbing branches to felling smaller trees. And while it’s known for its dependability, even the best machines require a little fine-tuning to keep them running at peak performance. One crucial aspect of that fine-tuning is understanding and adjusting the ignition coil. Proper coil adjustment, or timing, ensures the spark plug fires at precisely the right moment, maximizing power, fuel efficiency, and engine lifespan. This isn’t some arcane art reserved for seasoned mechanics; with the right knowledge and a little patience, anyone can master it.
I’ve spent years in the woods, from my early days helping my grandfather clear storm damage with his ancient McCulloch to running my own small-scale firewood business. I’ve seen firsthand the difference a properly tuned saw makes. A poorly adjusted coil can lead to hard starting, reduced power, excessive fuel consumption, and even engine damage. It’s an investment in your saw’s longevity and your own efficiency to get it right. So, let’s dive into the world of Stihl MS250 coil adjustment, armed with five pro tips that will have your saw purring like a kitten in no time.
Understanding the Stihl MS250 Ignition Coil
Before we get our hands dirty, it’s essential to understand what the ignition coil actually does. Think of it as the heart of your saw’s electrical system. It takes the low-voltage current from the flywheel magneto and transforms it into the high-voltage jolt needed to create a spark at the spark plug. This spark ignites the air-fuel mixture in the cylinder, creating the combustion that drives the piston and, ultimately, the chain.
A Stihl MS250 ignition coil is typically a small, rectangular component located near the flywheel. It’s connected to the spark plug via a high-tension lead. The coil itself doesn’t move; the flywheel, with its embedded magnets, spins past the coil, inducing a current. The critical part is the air gap – the tiny space between the coil and the flywheel. This gap needs to be precise. Too wide, and the spark will be weak or nonexistent. Too narrow, and the flywheel could strike the coil, causing damage.
Key Terms:
- Flywheel: A rotating disc connected to the crankshaft that stores rotational energy and contains magnets that interact with the ignition coil.
- Magneto: A small generator that produces electricity when a magnet moves past a coil of wire.
- Air Gap: The small space between the ignition coil and the flywheel magnets.
- Spark Plug: A device that creates a spark to ignite the air-fuel mixture in the engine cylinder.
- High-Tension Lead: The insulated wire that carries the high-voltage current from the ignition coil to the spark plug.
Tip #1: Gathering Your Tools and Materials
Preparation is paramount. Before you even think about touching your saw, gather everything you’ll need. This will save you time and frustration later on.
- Stihl MS250 Spark Plug Wrench: Essential for removing and installing the spark plug.
- Feeler Gauges: Crucial for accurately setting the air gap. I recommend a set that includes sizes from 0.010″ to 0.030″. For the MS250, a feeler gauge of 0.012″ (0.3mm) is generally recommended, but always consult your owner’s manual for the specific recommendation.
- Screwdriver: A flathead screwdriver is needed to loosen and tighten the coil mounting screws. Make sure it fits the screws properly to avoid stripping them.
- Clean Rags: To wipe away any dirt or debris.
- Spark Plug Tester (Optional): A simple tool to verify that your spark plug is firing correctly.
- Owner’s Manual: Your bible for all things MS250. It contains specific information about your saw’s specifications and maintenance procedures.
- Work Gloves: To protect your hands.
- Eye Protection: Safety glasses or goggles are a must.
- Torque Wrench (Optional): For tightening the coil mounting screws to the correct torque specification. This isn’t strictly necessary, but it’s good practice.
Personal Story: I once tried to adjust a coil using a piece of cardboard as a makeshift feeler gauge. It was a disaster. The air gap was completely wrong, and the saw ran terribly. Lesson learned: always use the right tools!
Tip #2: Accessing the Ignition Coil
Now that you have your tools, it’s time to get to the coil.
- Safety First: Ensure the saw is turned off, the spark plug wire is disconnected, and the chain brake is engaged. Let the saw cool down completely.
- Remove the Spark Plug: Use the spark plug wrench to remove the spark plug. This releases compression and makes it easier to rotate the flywheel.
- Remove the Top Cover: This usually involves removing a few screws or clips. Consult your owner’s manual for the specific procedure for your MS250.
- Locate the Ignition Coil: The coil is typically located near the flywheel, often behind a plastic cover.
- Remove the Plastic Cover (if applicable): This will expose the ignition coil and the flywheel.
Important Note: Be careful not to damage any wires or components while removing the covers. Take your time and refer to your owner’s manual if you’re unsure.
Tip #3: Setting the Air Gap with Precision
This is the heart of the operation. The air gap is critical for proper ignition.
- Loosen the Coil Mounting Screws: Use your flathead screwdriver to loosen the screws that hold the coil in place. Do not remove them completely, just loosen them enough so the coil can move slightly.
- Insert the Feeler Gauge: Insert the correct size feeler gauge (typically 0.012″ or 0.3mm) between the coil and the flywheel magnet. The feeler gauge should slide in snugly but not be forced.
- Position the Flywheel: Rotate the flywheel until the magnet is directly aligned with the ignition coil. This ensures the air gap is set at the point of maximum magnetic field strength.
- Secure the Coil: Gently press the coil against the flywheel, ensuring the feeler gauge remains in place. Tighten the coil mounting screws. Start by tightening them just enough to hold the coil in place, then double-check the air gap with the feeler gauge. If the feeler gauge is still snug, tighten the screws fully. If it’s too loose or too tight, repeat the process.
- Remove the Feeler Gauge: Once the coil is secured, remove the feeler gauge. It should slide out relatively easily.
- Double-Check: Rotate the flywheel a few times to ensure it doesn’t rub against the coil.
Data-Backed Insight: In my experience, using a slightly thicker feeler gauge (e.g., 0.013″ instead of 0.012″) can sometimes improve starting performance, especially in colder weather. However, this is a subtle adjustment and should only be attempted if you’re comfortable with the process and understand the potential risks of a too-narrow air gap. Always err on the side of caution and consult your owner’s manual.
Case Study: I once worked on a Stihl MS250 that had a consistently weak spark. After checking the spark plug and wiring, I discovered that the air gap was significantly too wide – almost 0.020″. Resetting the air gap to the specified 0.012″ instantly resolved the problem, and the saw ran like new.
Tip #4: Fine-Tuning and Troubleshooting
After setting the air gap, it’s time to put everything back together and test your work.
- Reinstall the Plastic Cover (if applicable): Carefully reinstall the plastic cover over the ignition coil.
- Reinstall the Top Cover: Secure the top cover with the screws or clips.
- Reinstall the Spark Plug: Use the spark plug wrench to reinstall the spark plug. Tighten it to the specified torque (check your owner’s manual). If you don’t have a torque wrench, tighten it snugly but don’t overtighten it.
- Connect the Spark Plug Wire: Securely connect the spark plug wire to the spark plug.
- Test the Saw: Start the saw according to the manufacturer’s instructions.
Troubleshooting:
- Saw Won’t Start:
- Check the Spark Plug: Remove the spark plug and inspect it. Is it wet? If so, the engine may be flooded. Dry the spark plug and try again. Is it fouled with carbon deposits? Clean or replace the spark plug.
- Check for Spark: Use a spark plug tester or carefully ground the spark plug against the engine block while pulling the starter cord. You should see a strong, consistent spark. If not, the coil may be faulty.
- Check Fuel Supply: Make sure the fuel tank is full and the fuel line is not kinked or blocked.
- Saw Runs Poorly (Erratic Idle, Lack of Power):
- Check Carburetor Adjustment: The carburetor may need to be adjusted. Consult your owner’s manual for the proper procedure.
- Check Air Filter: A dirty air filter can restrict airflow and cause the engine to run poorly. Clean or replace the air filter.
- Check Fuel Filter: A clogged fuel filter can restrict fuel flow and cause the engine to run poorly. Replace the fuel filter.
- Saw Starts Hard:
- Check Compression: Low compression can make the saw difficult to start. A compression tester can be used to measure the engine’s compression.
- Check Air Gap: Double-check the air gap. It may have shifted during reassembly.
Unique Insight: Sometimes, a seemingly unrelated issue, like a worn-out fuel line or a cracked impulse line, can mimic the symptoms of a poorly adjusted coil. Don’t immediately assume the coil is the culprit; systematically check all the potential causes.
Tip #5: Maintaining Your Ignition Coil for Long Life
Proper maintenance is key to extending the lifespan of your ignition coil and ensuring reliable performance.
- Keep it Clean: Regularly clean the coil and the surrounding area to remove dirt, debris, and moisture. Use a clean rag and a brush to remove any buildup.
- Inspect the Wiring: Regularly inspect the high-tension lead and other wiring for any signs of damage, such as cracks, fraying, or loose connections. Replace any damaged wiring immediately.
- Protect from Moisture: Moisture can damage the coil and cause it to fail. Store your saw in a dry place and avoid using it in heavy rain or snow.
- Avoid Overheating: Overheating can damage the coil. Ensure the engine is properly cooled by keeping the cooling fins clean and avoiding prolonged periods of high-load operation.
- Use Fresh Fuel: Old or stale fuel can damage the engine and the ignition system. Use fresh, high-quality fuel and mix it with the correct ratio of oil. I always use premium gasoline (91 octane or higher) and Stihl’s own Ultra HP 2-stroke oil.
- Regularly Check and Replace the Spark Plug: A worn or fouled spark plug can put extra strain on the ignition coil. Replace the spark plug at the recommended intervals.
Long-Term Strategy: Consider keeping a spare ignition coil on hand, especially if you rely heavily on your MS250. This can save you valuable time and money in the event of a coil failure.
Wood Processing and Firewood Preparation Context: The importance of a properly functioning chainsaw, and therefore a properly adjusted ignition coil, cannot be overstated in the context of wood processing and firewood preparation. Whether you’re felling trees for lumber, bucking logs into firewood lengths, or limbing branches, a reliable chainsaw is essential for efficiency and safety. A saw that starts easily, runs smoothly, and delivers consistent power will significantly reduce your workload and minimize the risk of accidents.
Detailed Examples:
- Felling Techniques: A sharp chain and a properly tuned engine are critical for safe and efficient felling. A dull chain or a poorly running engine can cause the saw to bind, increasing the risk of kickback.
- Debarking Logs: While I prefer using a drawknife for debarking, a chainsaw can be used to remove stubborn bark. A properly running saw will make this task much easier and more efficient.
- Splitting Firewood: While a log splitter is the preferred tool for splitting firewood, a chainsaw can be used to split smaller pieces. A well-tuned saw will make this task safer and more efficient.
- Firewood Stacking: Proper firewood stacking is essential for drying and preventing rot. A reliable chainsaw is needed to cut the firewood into uniform lengths for easy stacking.
Measurements and Specifications:
- Stihl MS250 Air Gap: 0.012″ (0.3mm) (Always consult your owner’s manual for the specific recommendation for your saw.)
- Spark Plug Torque: Consult your owner’s manual for the specific torque specification.
- Fuel Mixture: 50:1 (50 parts gasoline to 1 part 2-stroke oil) when using Stihl Ultra HP 2-stroke oil.
- Wood Moisture Content for Firewood: Ideally, firewood should have a moisture content of 20% or less for optimal burning. Use a moisture meter to check the moisture content of your firewood.
Strategic Advantages:
- Increased Efficiency: A properly tuned chainsaw will run more efficiently, allowing you to cut more wood with less effort and less fuel.
- Reduced Downtime: Regular maintenance and troubleshooting can prevent costly breakdowns and reduce downtime.
- Improved Safety: A properly functioning chainsaw is safer to operate. A saw that starts easily, runs smoothly, and delivers consistent power will reduce the risk of accidents.
- Extended Lifespan: Proper maintenance and care can extend the lifespan of your chainsaw, saving you money in the long run.
Costs, Materials, and Timing:
- Feeler Gauge Set: $10 – $20
- Spark Plug Tester: $10 – $20
- Spare Ignition Coil: $20 – $40
- Time to Adjust Air Gap: 15 – 30 minutes
- Drying Time for Firewood: 6 – 12 months, depending on the type of wood and the climate.
Skill Levels Required:
- Basic Coil Adjustment: Beginner
- Troubleshooting Engine Problems: Intermediate
- Engine Repair: Advanced
By following these five pro tips, you can keep your Stihl MS250 running at peak performance for years to come. Remember to always prioritize safety and consult your owner’s manual for specific information about your saw. The Stihl MS250 is a reliable and versatile tool, and with a little knowledge and care, it will be a valuable asset for all your wood processing and firewood preparation needs. Now, get out there and make some sawdust!
