Starting Stihl MS250 Troubleshooting Tips (5 Pro Fixes)
Let’s get down to brass tacks and dive into troubleshooting your Stihl MS250!
Starting Stihl MS250 Troubleshooting Tips (5 Pro Fixes)
If you’re anything like me, you rely on your chainsaw to get the job done, whether it’s felling trees, bucking logs for firewood, or just tidying up around the property. And when your trusty Stihl MS250 refuses to start, it’s more than just an inconvenience – it’s a real pain in the neck. I’ve been there, staring at a stubborn saw, wondering what in the world is going on. Over the years, I’ve learned a few tricks and fixes that have saved me countless hours and a whole lot of frustration.
I remember one particular incident vividly. I was helping a friend clear some land for a new barn. We were working with a mix of oak and maple, tough hardwoods that demand a reliable saw. My MS250 was running like a champ until, suddenly, it sputtered and died. After a few minutes of frantic troubleshooting, it turned out to be a simple clogged fuel filter. Since then, I always carry a spare filter and a small tool kit in my truck.
This guide is designed to help you diagnose and fix common starting problems with your Stihl MS250. We’ll cover everything from the basics to some more advanced troubleshooting techniques. I’ll share my personal experiences and insights, along with data-backed information and practical tips to get your saw roaring back to life.
1. Fuel System Check: The Lifeline of Your Saw
The fuel system is the heart of your chainsaw. Without a proper supply of clean fuel, your MS250 simply won’t start. Let’s break down the key components and how to troubleshoot them.
a. Fuel Quality and Mixture: Is Your Gas Fresh?
Old fuel is a common culprit when your chainsaw refuses to start. Gasoline degrades over time, especially when mixed with oil. I always recommend using fresh, high-quality gasoline with an octane rating of 89 or higher. Stihl recommends a fuel mix ratio of 50:1 (gasoline to two-cycle engine oil). Using the wrong ratio can lead to engine damage or starting problems.
Pro Tip: I always write the date on my fuel cans with a permanent marker. If the fuel is more than a month old, I discard it or use it in my car (if it’s straight gasoline).
Data Point: Studies have shown that gasoline can lose up to 50% of its octane rating in just six months when stored improperly.
b. Fuel Filter: Is it Clogged?
The fuel filter prevents debris from entering the carburetor. A clogged filter restricts fuel flow, making it difficult to start the saw. To check the fuel filter:
- Remove the fuel cap and use a clean wire or hook to pull the fuel filter out of the tank.
- Inspect the filter for dirt and debris.
- If the filter is clogged, replace it with a new one.
My Experience: I once spent an hour trying to start my MS250 before realizing the fuel filter was completely blocked with sawdust. Since then, I inspect and replace the fuel filter regularly.
c. Fuel Lines: Are They Cracked or Leaking?
Fuel lines can become brittle and cracked over time, leading to fuel leaks and air entering the fuel system. Inspect the fuel lines for any signs of damage. Replace any cracked or leaking fuel lines with new ones.
How-To: To inspect fuel lines, remove the air filter cover and visually inspect the lines. You may need to remove the carburetor to get a better view. Look for cracks, kinks, or signs of fuel leakage.
d. Fuel Tank Vent: Is It Blocked?
The fuel tank vent allows air to enter the fuel tank, preventing a vacuum from forming. If the vent is blocked, fuel cannot flow properly to the carburetor.
Troubleshooting: Remove the fuel cap and try starting the saw. If it starts, the fuel tank vent is likely blocked. Clean the vent with compressed air or a small wire.
2. Spark Plug Check: Igniting the Fire
The spark plug ignites the fuel-air mixture in the cylinder, starting the engine. A faulty spark plug is a common cause of starting problems.
a. Visual Inspection: Is It Fouled?
Remove the spark plug and inspect it for signs of fouling, such as carbon buildup or oil deposits. A fouled spark plug will not produce a strong spark.
Data Point: A spark plug should be replaced every 100 hours of operation or annually, whichever comes first.
b. Spark Test: Is It Sparking?
To test the spark plug, connect it to the spark plug wire and ground it against the engine block. Pull the starter rope and observe the spark. A healthy spark should be strong and blue. If the spark is weak or non-existent, replace the spark plug.
Safety First: Always disconnect the spark plug wire from the spark plug before removing it to prevent accidental starting.
Unique Insight: The color of the spark plug can tell you a lot about your engine’s condition. A black, sooty spark plug indicates a rich fuel mixture, while a white, ashy spark plug indicates a lean fuel mixture.
c. Spark Plug Replacement: A Simple Solution
Replacing the spark plug is a quick and easy fix that can often resolve starting problems. Use the correct spark plug for your Stihl MS250 (typically an NGK BPMR7A or Champion RCJ6Y).
Personal Story: I once spent hours troubleshooting a starting problem only to discover that the spark plug was the culprit. It looked fine at first glance, but it was internally damaged and not producing a consistent spark.
3. Carburetor Examination: The Fuel-Air Mixer
The carburetor mixes fuel and air in the correct proportions for combustion. A dirty or malfunctioning carburetor can cause starting problems, poor performance, and engine damage.
a. Air Filter: Is It Clean?
A dirty air filter restricts airflow to the carburetor, causing a rich fuel mixture. This can make it difficult to start the saw and reduce engine power.
Best Practice: Clean the air filter regularly with soap and water. Allow it to dry completely before reinstalling it. I clean mine after every 5-8 hours of use, depending on the conditions.
b. Carburetor Cleaning: A Necessary Task
Over time, the carburetor can become clogged with dirt, varnish, and other deposits. Cleaning the carburetor can often restore proper fuel-air mixture and resolve starting problems.
How-To:
- Remove the air filter and carburetor cover.
- Disconnect the fuel lines and throttle linkage from the carburetor.
- Remove the carburetor from the engine.
- Disassemble the carburetor and clean all parts with carburetor cleaner.
- Reassemble the carburetor and reinstall it on the engine.
Caution: Carburetor cleaner is flammable and can irritate the skin. Use it in a well-ventilated area and wear gloves and eye protection.
Advanced Tip: If you’re not comfortable disassembling the carburetor yourself, you can take it to a qualified mechanic for cleaning.
c. Carburetor Adjustment: Fine-Tuning Performance
The carburetor has adjustment screws that control the fuel-air mixture. Adjusting these screws can improve starting, idling, and overall performance.
Understanding the Screws:
- L (Low-Speed) Screw: Controls the fuel-air mixture at idle and low speeds.
- H (High-Speed) Screw: Controls the fuel-air mixture at high speeds.
- LA (Idle Speed) Screw: Controls the engine’s idle speed.
Adjustment Procedure:
- Start the engine and let it warm up.
- Adjust the LA screw until the engine idles smoothly without stalling.
- Adjust the L screw until the engine accelerates smoothly from idle to full throttle.
- Adjust the H screw until the engine runs smoothly at full throttle without bogging down.
Important Note: Carburetor adjustment is a delicate process. Make small adjustments and listen carefully to the engine’s response. If you’re unsure how to adjust the carburetor, consult a qualified mechanic.
My Troubleshooting Strategy: I usually start by cleaning the air filter and then adjusting the low-speed screw (L). Often, a slight adjustment is all it takes to get the saw running smoothly again.
4. Ignition System Investigation: The Spark Source
The ignition system generates the spark that ignites the fuel-air mixture in the cylinder. If the ignition system is faulty, the saw will not start.
a. Ignition Coil: Is It Working?
The ignition coil generates the high-voltage spark that is sent to the spark plug. A faulty ignition coil can prevent the saw from starting.
Testing the Ignition Coil:
- Disconnect the spark plug wire from the spark plug.
- Use a multimeter to measure the resistance between the spark plug wire terminal and the engine ground.
- The resistance should be within the range specified in the service manual.
If the resistance is outside the specified range, the ignition coil is likely faulty and needs to be replaced.
b. Flywheel Key: Is It Sheared?
The flywheel key aligns the flywheel with the crankshaft. If the key is sheared, the timing will be off, and the saw will not start.
Checking the Flywheel Key:
- Remove the starter assembly and flywheel cover.
- Inspect the flywheel key for any signs of damage.
- If the key is sheared, replace it with a new one.
Real-World Example: I once had a Stihl MS250 that wouldn’t start no matter what I did. After checking everything else, I finally discovered that the flywheel key was sheared. Replacing the key fixed the problem immediately.
c. Kill Switch: Is It Functioning Properly?
The kill switch grounds the ignition system, stopping the engine. If the kill switch is faulty, it may prevent the saw from starting.
Testing the Kill Switch:
- Disconnect the kill switch wire from the ignition coil.
- Try starting the saw.
- If the saw starts, the kill switch is likely faulty and needs to be replaced.
5. Compression Check: The Engine’s Health
Compression is the pressure created in the cylinder when the piston moves up and down. Low compression can prevent the saw from starting.
a. Compression Tester: Measuring the Pressure
A compression tester is a gauge that measures the compression in the cylinder.
How-To:
- Remove the spark plug.
- Insert the compression tester into the spark plug hole.
- Pull the starter rope several times.
- Record the compression reading.
Data Point: A healthy Stihl MS250 should have a compression reading of at least 120 PSI.
b. Low Compression Causes: Identifying the Culprit
Low compression can be caused by several factors, including:
- Worn Piston Rings: Piston rings seal the space between the piston and the cylinder wall. Worn piston rings allow compression to escape.
- Damaged Cylinder: A damaged cylinder can also cause low compression.
- Leaky Valves: Valves seal the combustion chamber. Leaky valves allow compression to escape.
Addressing Low Compression:
If your Stihl MS250 has low compression, it may need to be repaired or replaced. Depending on the severity of the problem, you may be able to replace the piston rings or valves. In some cases, the entire engine may need to be replaced.
Case Study: I worked on a Stihl MS250 that had been used heavily for firewood production. The compression was only 90 PSI. After disassembling the engine, I found that the piston rings were worn and the cylinder was scored. I replaced the piston, rings, and cylinder, and the compression returned to 130 PSI.
Additional Tips and Tricks
- Check the Starter Rope: A frayed or broken starter rope can prevent you from starting the saw. Replace the starter rope if it is damaged.
- Use a Starting Fluid: A shot of starting fluid can help the engine start if it is having trouble getting fuel. However, use starting fluid sparingly, as it can damage the engine if used excessively.
- Consult a Professional: If you’ve tried all of these troubleshooting tips and your Stihl MS250 still won’t start, it’s time to consult a qualified mechanic.
Preventative Maintenance: Keeping Your Saw in Top Shape
Regular maintenance is key to preventing starting problems and keeping your Stihl MS250 running smoothly.
- Clean the Air Filter Regularly: As mentioned earlier, a clean air filter is essential for proper engine performance.
- Replace the Fuel Filter Annually: A new fuel filter ensures a steady supply of clean fuel to the carburetor.
- Replace the Spark Plug Annually: A new spark plug ensures a strong and consistent spark.
- Sharpen the Chain Regularly: A sharp chain cuts more efficiently and reduces strain on the engine.
- Store the Saw Properly: When storing the saw for an extended period, drain the fuel tank and run the engine until it stalls. This prevents fuel from gumming up the carburetor.
Wood Species and Their Impact on Chainsaw Performance
The type of wood you’re cutting can also affect your chainsaw’s performance and starting ability. Hardwoods like oak and maple require more power than softwoods like pine and fir. Using a dull chain on hardwoods can put extra strain on the engine and make it harder to start.
Data Point: Hardwoods can be up to three times denser than softwoods, requiring significantly more power to cut.
My Woodworking Philosophy: I always try to match my chainsaw and chain to the type of wood I’m cutting. For hardwoods, I use a sharp chain and a higher-powered saw. For softwoods, I can get away with a slightly duller chain and a smaller saw.
Safety Considerations: Working with Chainsaws Responsibly
Working with chainsaws can be dangerous. Always wear appropriate safety gear, including:
- Eye Protection: Safety glasses or a face shield to protect your eyes from flying debris.
- Hearing Protection: Earplugs or earmuffs to protect your hearing from the loud noise of the chainsaw.
- Gloves: Heavy-duty gloves to protect your hands from cuts and abrasions.
- Chaps: Chainsaw chaps to protect your legs from accidental cuts.
- Steel-Toed Boots: Steel-toed boots to protect your feet from falling logs and other hazards.
Remember: Never operate a chainsaw when you are tired, under the influence of drugs or alcohol, or in poor weather conditions.
Final Thoughts
Troubleshooting a Stihl MS250 that won’t start can be frustrating, but with a systematic approach and a little patience, you can usually diagnose and fix the problem yourself. Remember to start with the basics, such as checking the fuel quality and spark plug, and then move on to more advanced troubleshooting techniques, such as cleaning the carburetor and testing the ignition system. And always prioritize safety when working with chainsaws. By following these tips, you can keep your Stihl MS250 running smoothly for years to come. Now, get out there and get cutting!
