Problem Starting Stihl Chainsaw: MS 250 Won't Start (Troubleshooting Tips)

As the days grow shorter and a crispness fills the air, my thoughts, like yours, likely turn to the comforting warmth of a crackling fire. But before we can settle in with a mug of hot cocoa and a good book, there’s the small matter of preparing the fuel. And that often starts with a reliable chainsaw. When that trusty Stihl MS 250 refuses to cooperate, frustration can quickly set in. I know the feeling all too well. I’ve spent countless hours in the woods, and a temperamental chainsaw can throw a serious wrench into any wood-cutting plan. So, if your MS 250 won’t start, don’t despair! This guide is designed to walk you through the troubleshooting process, step-by-step, so you can get back to the business of preparing for winter. We’ll cover everything from basic checks to more in-depth diagnostics, all based on my years of experience and a good dose of practical knowledge. Let’s get that saw roaring again!

Problem Starting Stihl Chainsaw: MS 250 Won’t Start (Troubleshooting Tips)

Before diving into the nitty-gritty, let’s frame the situation. The global firewood market is a substantial one, driven by both residential heating needs and recreational use. According to recent reports, the global firewood market was valued at over $10 billion USD in 2023 and is projected to grow in the coming years. This demand underscores the importance of efficient and reliable tools like the Stihl MS 250, a popular choice for both homeowners and professionals. When it fails, productivity grinds to a halt.

Let’s get one thing straight. Chainsaws are essential for wood processing, but they are not infallible. They require regular maintenance and a good understanding of their mechanics. The Stihl MS 250, known for its balance of power and maneuverability, is a workhorse. But even the best tools can have their off days.

Understanding the Fundamentals: Why Chainsaws Fail to Start

Before we start tinkering, it’s crucial to understand why a chainsaw might refuse to start. The most common culprits include:

Fuel Issues: Stale fuel, incorrect fuel mixture, or a clogged fuel filter.
Ignition Problems: A faulty spark plug or a malfunctioning ignition module.
Airflow Obstructions: A dirty air filter preventing proper combustion.
Carburetor Problems: A clogged or improperly adjusted carburetor.
Compression Issues: Low compression due to a worn piston or cylinder.

These issues, either alone or in combination, can prevent the engine from firing up. Let’s tackle them systematically.

Step-by-Step Troubleshooting Guide for Your Stihl MS 250

I’ve organized this guide into a series of steps, starting with the simplest checks and progressing to more complex diagnostics. Remember to always prioritize safety. Wear gloves and eye protection when working on your chainsaw.

Step 1: The Obvious Checks – Fuel and Power

This might seem like stating the obvious, but you’d be surprised how often simple oversights are the cause of the problem.

Check the Fuel Tank: Make sure there’s fuel in the tank! It sounds silly, but it happens. Also, ensure the fuel is fresh. Gasoline can degrade over time, especially when mixed with oil. A good rule of thumb is to use fuel that’s no more than 30 days old. If the fuel looks cloudy or smells stale, drain the tank and replace it with fresh fuel.
Verify the Fuel Mixture: Stihl chainsaws, including the MS 250, require a specific fuel-to-oil ratio. Typically, this is 50:1 (50 parts gasoline to 1 part two-stroke oil). Using the wrong mixture can lead to engine damage or starting problems. I always recommend using a high-quality two-stroke oil designed for air-cooled engines. Pre-mixed fuel is available, but it’s often more expensive. I prefer mixing my own to ensure I’m using the correct ratio and a quality oil.
Check the On/Off Switch: Make sure the switch is in the “ON” or “I” position. Again, it sounds simple, but it’s easily overlooked.
Engage the Chain Brake: Ensure the chain brake is disengaged. The chainsaw won’t start if the brake is engaged as a safety feature.

Step 2: Priming and Choke – Getting the Fuel Flowing

The priming bulb and choke are crucial for getting fuel into the carburetor, especially when the engine is cold.

Prime the Carburetor: Locate the priming bulb (a small, clear bulb near the carburetor). Press it firmly several times (usually 5-10 times) until you see fuel flowing through it. This draws fuel from the tank into the carburetor.
Engage the Choke: The choke restricts airflow to the engine, creating a richer fuel mixture for starting. On the MS 250, the choke lever is usually located near the carburetor. When the engine is cold, engage the choke fully. For a warm engine, you may not need to use the choke at all, or only partially.
Pull the Starter Cord: With the choke engaged, pull the starter cord firmly and smoothly. Don’t yank it! Pull until you hear the engine “pop” or sputter briefly. This indicates that the engine is trying to start.
Disengage the Choke: Once the engine pops, disengage the choke (or move it to the half-choke position if your model has one). Now, pull the starter cord again to start the engine.
Troubleshooting the Prime/Choke: If priming the bulb doesn’t seem to draw fuel, or if the choke doesn’t seem to make a difference, there may be a blockage in the fuel lines or carburetor. We’ll address that later.

Step 3: Spark Plug Inspection – The Heart of the Ignition

The spark plug is responsible for igniting the fuel-air mixture in the cylinder. A faulty spark plug can prevent the engine from starting.

Locate the Spark Plug: The spark plug is typically located under a rubber boot near the cylinder head.
Remove the Spark Plug: Carefully remove the rubber boot and use a spark plug wrench to unscrew the spark plug.
Inspect the Spark Plug: Examine the spark plug for signs of damage, such as cracks, excessive carbon buildup, or a worn electrode. A healthy spark plug should have a clean, tan-colored electrode.
Clean the Spark Plug: If the spark plug is dirty, clean it with a wire brush. You can also use a spark plug cleaner, if you have one.
Check the Spark Gap: The spark gap is the distance between the electrode and the ground electrode. The correct spark gap for the Stihl MS 250 is typically around 0.020 inches (0.5 mm). Use a spark plug gap tool to measure and adjust the gap if necessary.
Test for Spark: Reconnect the spark plug to the rubber boot and hold the electrode against the engine cylinder. Pull the starter cord. You should see a strong, blue spark jumping across the gap. If there’s no spark, or the spark is weak and yellow, the spark plug is likely faulty and needs to be replaced. It could also indicate a problem with the ignition coil.
Replace the Spark Plug: If the spark plug is damaged, dirty, or not producing a strong spark, replace it with a new one. Use the correct spark plug for the Stihl MS 250 (typically a NGK BPMR7A or equivalent).
Reinstall the Spark Plug: Screw the spark plug back into the cylinder head, tightening it to the manufacturer’s specifications. Reattach the rubber boot.

Step 4: Air Filter Examination – Breathing Easy for Combustion

A clean air filter is essential for proper combustion. A dirty air filter restricts airflow, leading to a lean fuel mixture and starting problems.

Locate the Air Filter: The air filter is typically located under a cover on the side of the engine.
Remove the Air Filter: Remove the cover and take out the air filter.
Inspect the Air Filter: Examine the air filter for dirt, dust, and debris. A heavily soiled air filter will be visibly clogged.
Clean the Air Filter: If the air filter is only slightly dirty, you can clean it by tapping it gently against a hard surface or using compressed air to blow the dirt out. For heavily soiled air filters, wash them with warm, soapy water. Rinse thoroughly and allow to dry completely before reinstalling.
Replace the Air Filter: If the air filter is damaged or excessively dirty, replace it with a new one.
Reinstall the Air Filter: Place the cleaned or new air filter back in its housing and reinstall the cover.

Step 5: Fuel Filter Check – Ensuring a Clean Fuel Supply

The fuel filter prevents dirt and debris from entering the carburetor. A clogged fuel filter can restrict fuel flow and cause starting problems.

Locate the Fuel Filter: The fuel filter is located inside the fuel tank, attached to the end of the fuel line.
Access the Fuel Filter: Use a piece of bent wire or a specialized fuel filter removal tool to carefully pull the fuel filter out of the tank.
Inspect the Fuel Filter: Examine the fuel filter for dirt, debris, and clogs. A heavily clogged fuel filter will be visibly dirty.
Replace the Fuel Filter: If the fuel filter is dirty or clogged, replace it with a new one. These are inexpensive and should be replaced regularly as preventative maintenance.
Reinstall the Fuel Filter: Attach the new fuel filter to the end of the fuel line and carefully insert it back into the fuel tank.

Step 6: Carburetor Diagnostics – The Heart of the Fuel System

The carburetor is responsible for mixing fuel and air in the correct proportions for combustion. A clogged or improperly adjusted carburetor can cause a variety of problems, including starting difficulties.

Visual Inspection: Start by visually inspecting the carburetor for any signs of damage, such as cracks or leaks.
Carburetor Cleaning (Simple): Sometimes, a simple cleaning can resolve minor carburetor issues. Remove the air filter and spray carburetor cleaner directly into the carburetor intake while pulling the starter cord. This can help to dissolve any deposits that may be blocking the jets.
Carburetor Adjustment Screws: The carburetor has adjustment screws (typically labeled “H” for high-speed and “L” for low-speed) that control the fuel-air mixture. Improper adjustment can cause starting problems. The factory settings are a good starting point, but they may need to be fine-tuned.
- Finding the Factory Settings: Consult your Stihl MS 250 owner’s manual for the factory settings for the “H” and “L” screws. These settings are usually expressed as the number of turns out from the fully closed position.
- Adjusting the Screws: Using a small screwdriver, gently turn the “H” and “L” screws to their factory settings. Then, try starting the chainsaw. If it still doesn’t start, you may need to fine-tune the adjustments.
- Fine-Tuning (Advanced): This requires a bit of experience and a good ear. Start the chainsaw (if possible) and let it warm up. Then, adjust the “L” screw until the engine idles smoothly without stalling. Next, adjust the “H” screw for optimal performance at high speeds. Be careful not to lean out the mixture too much, as this can damage the engine. If you are not comfortable with this, take it to a professional.
Complete Carburetor Cleaning (Advanced): If the simple cleaning doesn’t work, you may need to disassemble and clean the carburetor more thoroughly. This is a more complex procedure and requires some mechanical skill.
- Disassembly: Carefully disassemble the carburetor, taking note of the location of each part. It’s helpful to take pictures as you go, so you can remember how everything goes back together.
- Cleaning: Clean all the carburetor parts with carburetor cleaner. Pay particular attention to the jets, which are tiny openings that can easily become clogged. Use a small wire or a carburetor cleaning tool to clear any blockages.
- Reassembly: Reassemble the carburetor, making sure all the parts are properly seated.
- Reinstallation: Reinstall the carburetor on the chainsaw.

Important Note: Carburetor work can be tricky. If you’re not comfortable disassembling and cleaning the carburetor yourself, it’s best to take it to a qualified mechanic.

Step 7: Compression Testing – A Sign of Engine Health

Compression is the pressure created in the cylinder when the piston moves up. Low compression can indicate a worn piston, cylinder, or rings, which can prevent the engine from starting.

Obtain a Compression Tester: You’ll need a compression tester to perform this test. These are available at most auto parts stores.
Remove the Spark Plug: Remove the spark plug from the cylinder head.
Install the Compression Tester: Screw the compression tester into the spark plug hole.
Pull the Starter Cord: Pull the starter cord repeatedly until the needle on the compression tester stops rising.
Read the Compression: Note the reading on the compression tester. The Stihl MS 250 should have a compression reading of at least 120 PSI (pounds per square inch).
Interpret the Results:
- High Compression: If the compression reading is within the normal range, the piston, cylinder, and rings are likely in good condition.
- Low Compression: If the compression reading is below 120 PSI, there may be a problem with the piston, cylinder, or rings. This could be due to wear and tear, damage, or a blown head gasket.

Important Note: Low compression can be a sign of serious engine damage. If you suspect low compression, it’s best to take the chainsaw to a qualified mechanic for further diagnosis and repair.

Step 8: Checking the Ignition Coil – The Spark’s Source

The ignition coil generates the high-voltage spark that ignites the fuel-air mixture. A faulty ignition coil can prevent the engine from starting.

Locate the Ignition Coil: The ignition coil is typically located near the flywheel.
Test for Spark (Again): Even if you tested the spark plug earlier, it’s worth re-testing after checking other components. Follow the same procedure as in Step 3, holding the spark plug electrode against the engine cylinder while pulling the starter cord.
Check the Ignition Coil Wiring: Inspect the wiring connected to the ignition coil for any signs of damage, such as frayed wires or loose connections.
Test the Ignition Coil with a Multimeter (Advanced): This requires a multimeter and some electrical knowledge.
- Disconnect the Ignition Coil: Disconnect the ignition coil from the wiring harness.
- Set the Multimeter: Set the multimeter to measure resistance (ohms).
- Measure the Resistance: Measure the resistance between the primary and secondary terminals of the ignition coil. The resistance values should be within the manufacturer’s specifications. Consult your Stihl MS 250 service manual for the correct resistance values.
- Interpret the Results: If the resistance values are outside the specified range, the ignition coil is likely faulty and needs to be replaced.

Important Note: Working with electrical components can be dangerous. If you’re not comfortable testing the ignition coil with a multimeter, it’s best to take the chainsaw to a qualified mechanic.

Step 9: Exhaust System Check – Clearing the Path for Combustion

A clogged exhaust system can restrict the flow of exhaust gases, leading to backpressure and starting problems.

Inspect the Spark Arrestor: The spark arrestor is a small screen located in the muffler that prevents sparks from escaping. A clogged spark arrestor can restrict exhaust flow.
- Locate the Spark Arrestor: The spark arrestor is usually accessible by removing a small cover on the muffler.
- Remove the Spark Arrestor: Remove the cover and take out the spark arrestor screen.
- Clean the Spark Arrestor: Clean the spark arrestor screen with a wire brush. You can also use carburetor cleaner to dissolve any deposits.
- Reinstall the Spark Arrestor: Reinstall the cleaned spark arrestor screen and cover.
Inspect the Muffler: Check the muffler for any signs of damage or blockage. A severely damaged or clogged muffler can restrict exhaust flow.
Check the Exhaust Port: The exhaust port is the opening in the cylinder head where exhaust gases exit the engine. A clogged exhaust port can restrict exhaust flow.
- Locate the Exhaust Port: The exhaust port is located behind the muffler.
- Remove the Muffler: Remove the muffler to access the exhaust port.
- Inspect the Exhaust Port: Inspect the exhaust port for carbon buildup or other obstructions.
- Clean the Exhaust Port: Clean the exhaust port with a scraper or a wire brush.
- Reinstall the Muffler: Reinstall the muffler.

Step 10: Diagnosing a Flooded Engine – Too Much of a Good Thing

Sometimes, the engine can become flooded with fuel, especially after repeated attempts to start it. This can prevent the engine from starting.

Remove the Spark Plug: Remove the spark plug from the cylinder head.
Pull the Starter Cord: Pull the starter cord repeatedly to clear the excess fuel from the cylinder.
Dry the Spark Plug: Dry the spark plug with a clean cloth.
Reinstall the Spark Plug: Reinstall the spark plug.
Start the Engine Without Choke: Try starting the engine without using the choke.

Step 11: Rope and Recoil Spring – Check the Starter

If the starter rope is hard to pull, doesn’t retract properly, or is broken, it can prevent you from starting the chainsaw.

Inspect the Rope: Look for fraying, cuts, or other damage to the starter rope. Replace the rope if it’s damaged.
Check the Recoil Spring: If the rope doesn’t retract properly, the recoil spring might be broken or weak. You’ll need to disassemble the starter assembly to inspect and replace the spring. This can be a bit tricky, so be careful and take pictures as you go.
Lubricate the Mechanism: Sometimes, the starter mechanism can become stiff due to dirt or lack of lubrication. Clean the mechanism and apply a light lubricant.

Case Study: Reviving a Neglected MS 250

I once acquired a used Stihl MS 250 from a friend who had left it sitting in his garage for several years. It wouldn’t start, and he was ready to give up on it. I took it as a challenge. After a thorough inspection, I found the following issues:

Stale Fuel: The fuel in the tank was old and cloudy.
Clogged Fuel Filter: The fuel filter was completely blocked with debris.
Dirty Air Filter: The air filter was covered in dust and dirt.
Dirty Spark Plug: The spark plug was fouled with carbon buildup.
Slightly Clogged Carburetor: The carburetor jets were partially blocked.

I systematically addressed each of these issues:

Drained the Fuel Tank: I drained the old fuel and replaced it with fresh fuel and the correct oil mixture.
Replaced the Fuel Filter: I installed a new fuel filter.
Cleaned the Air Filter: I washed the air filter with warm, soapy water and allowed it to dry completely.
Cleaned the Spark Plug: I cleaned the spark plug with a wire brush and checked the spark gap.
Cleaned the Carburetor: I disassembled the carburetor and cleaned all the parts with carburetor cleaner.

After reassembling everything, the chainsaw started on the second pull! It ran smoothly and powerfully. This experience reinforced the importance of regular maintenance and the impact of even seemingly minor issues on chainsaw performance.

Common Pitfalls and How to Avoid Them

Even with the best instructions, it’s easy to make mistakes. Here are some common pitfalls to avoid:

Using the Wrong Fuel Mixture: Always use the correct fuel-to-oil ratio. Too much oil can foul the spark plug, while too little oil can damage the engine.
Over-Tightening the Spark Plug: Tighten the spark plug to the manufacturer’s specifications. Over-tightening can damage the cylinder head.
Forgetting to Reconnect Wires: When disassembling components, be careful not to forget to reconnect any wires or hoses.
Using the Wrong Parts: Always use the correct replacement parts for your Stihl MS 250. Using the wrong parts can damage the engine or affect performance.
Ignoring Safety Precautions: Always wear gloves and eye protection when working on your chainsaw.

Budgeting for Repairs and Maintenance

Chainsaw maintenance and repairs can add up over time. Here’s a rough estimate of the costs you might encounter:

Fuel Filter: $5 – $10
Air Filter: $5 – $15
Spark Plug: $5 – $10
Carburetor Cleaner: $5 – $10
Carburetor Rebuild Kit: $20 – $50
Ignition Coil: $30 – $70
Compression Tester: $30 – $100
Professional Repair: $50 – $150 per hour

To save money, perform as much maintenance as you can yourself. Regular cleaning and filter replacements can prevent more costly repairs down the road.

Next Steps and Additional Resources

If you’ve followed all the troubleshooting steps and your Stihl MS 250 still won’t start, it’s time to seek professional help. A qualified mechanic can diagnose and repair more complex issues, such as internal engine damage.

Here are some additional resources that you may find helpful:

Stihl MS 250 Owner’s Manual: This manual contains valuable information about the chainsaw’s operation, maintenance, and troubleshooting.
Stihl Website: The Stihl website offers a wealth of information about Stihl products, including parts diagrams, service manuals, and FAQs.
Online Forums: There are many online forums dedicated to chainsaws and outdoor power equipment. These forums can be a great source of information and support from other users.
Local Stihl Dealer: Your local Stihl dealer can provide expert advice, parts, and service for your Stihl MS 250.

Suppliers of Logging Tools and Drying Equipment:

Problem Starting Stihl Chainsaw: MS 250 Won’t Start (Troubleshooting Tips)