Starting Stihl MS 250: Troubleshooting Tips (5 Pro Logging Fixes)

Alright, let’s dive into the frustrating world of a Stihl MS 250 that refuses to cooperate. There’s nothing quite like the anticipation of a productive day turning sour when your chainsaw won’t fire up. I know that feeling all too well! I’ve spent countless hours in the woods, relying on my Stihl MS 250 to get the job done, and I’ve definitely encountered my fair share of starting issues.

The Stihl MS 250 is a workhorse, a reliable companion for limbing, felling smaller trees, and bucking firewood. Its compact size and decent power-to-weight ratio make it a favorite among homeowners and professionals alike. But even the best tools can have their off days. When your MS 250 decides to be stubborn, it can throw a wrench into your entire operation.

In this article, I’m going to share my hard-earned knowledge and experience to help you troubleshoot a Stihl MS 250 that won’t start. I’ll cover five common issues, provide step-by-step instructions for diagnosing and fixing them, and offer some preventative maintenance tips to keep your saw running smoothly for years to come. Let’s get this saw roaring again!

Key Takeaways:

• Fuel Issues: Old or contaminated fuel is a common culprit. Learn how to identify and address fuel-related problems.
• Spark Problems: A faulty spark plug or ignition system can prevent the engine from firing. We’ll cover how to test and replace these components.
• Carburetor Problems: A clogged or misadjusted carburetor can disrupt the fuel-air mixture. I’ll guide you through cleaning and adjusting the carb.
• Air Filter Problems: A dirty air filter can restrict airflow and choke the engine. I’ll show you how to clean or replace the air filter.
• Compression Issues: Low compression can indicate serious engine damage. We’ll discuss how to check compression and what to do if it’s low.

Starting Stihl MS 250: Troubleshooting Tips (5 Pro Logging Fixes)

The Comfort of a Reliable Chainsaw: Setting the Stage

There’s a unique comfort that comes from knowing your chainsaw will start when you need it to. It’s the confidence that allows you to venture into the woods, tackle demanding tasks, and efficiently process wood for warmth or projects. That feeling is quickly replaced by frustration when your reliable Stihl MS 250 decides to act up.

I remember one particularly cold December morning. The woodstove was barely keeping up, and the forecast called for a major snowstorm. I needed to get a good supply of firewood cut and stacked before the storm hit. I pulled out my trusty MS 250, gave the cord a yank, and… nothing. Again. Still nothing. A sinking feeling washed over me as I realized my firewood supply was hanging in the balance, and my reliable saw had let me down.

After a few choice words and some frantic troubleshooting, I managed to get it running (it was a clogged fuel filter, by the way). But that experience taught me a valuable lesson: knowing how to diagnose and fix common chainsaw problems is essential for anyone who relies on these tools.

This article is born from those experiences – the successes and the frustrations – of working with chainsaws in real-world conditions. I want to share the knowledge I’ve gained over the years to help you keep your Stihl MS 250 running smoothly and avoid those frustrating starting problems.

1. Fuel Issues: The Lifeblood of Your Chainsaw

The Problem: Old, contaminated, or improperly mixed fuel is one of the most common reasons why a chainsaw won’t start. Gasoline degrades over time, especially when mixed with oil. This degradation can lead to gum and varnish buildup in the fuel system, clogging fuel lines, filters, and carburetor jets.

Why it Matters: According to a study by the Outdoor Power Equipment Institute (OPEI), over 70% of small engine problems are fuel-related. Using old or improperly mixed fuel can significantly reduce engine performance, increase emissions, and even cause permanent damage.

My Experience: I once had a Stihl MS 250 that refused to start after sitting idle for a few months. I assumed the problem was something complex, but after checking the basics, I realized the fuel in the tank was stale and had a distinct varnish-like smell. Draining the old fuel, cleaning the tank, and replacing it with fresh, properly mixed fuel solved the problem instantly.

Troubleshooting Steps:

1. Check the Fuel:
   • Smell: Does the fuel smell fresh, or does it have a stale, varnish-like odor? Stale fuel is a sign of degradation.
   • Appearance: Is the fuel clear and bright, or is it cloudy or discolored? Cloudy fuel can indicate water contamination.
   • Age: How long has the fuel been sitting in the tank? Fuel older than 30 days is likely to have degraded.
2. Drain the Old Fuel:
   • Carefully drain the old fuel from the tank into an approved container. Dispose of the fuel properly according to local regulations.
3. Inspect the Fuel Filter:
   • The fuel filter is located inside the fuel tank, attached to the end of the fuel line.
   • Use a piece of wire or a hooked tool to carefully pull the fuel filter out of the tank.
   • Inspect the filter for clogs or debris.
   • If the filter is dirty, replace it with a new one. Stihl part number 0000-350-3500 is the correct replacement.
4. Mix Fresh Fuel:
   • Use a high-quality, 89-octane or higher gasoline.
   • Mix the gasoline with a 2-cycle engine oil specifically designed for chainsaws.
   • Follow the manufacturer’s recommended mixing ratio. For Stihl MS 250, the ratio is typically 50:1 (50 parts gasoline to 1 part oil). Using Stihl’s HP Ultra oil can extend engine life.
   • Use a calibrated mixing container to ensure accurate measurements.
   • Mix only the amount of fuel you need for the day to minimize waste.
5. Refill the Fuel Tank:
   • Carefully pour the fresh fuel mixture into the fuel tank.
   • Avoid spilling fuel, as it can damage the saw and create a fire hazard.

Pro Tip: Use a fuel stabilizer additive to extend the life of your fuel. Fuel stabilizers prevent the fuel from degrading and forming gum and varnish deposits. I personally recommend using STA-BIL Fuel Stabilizer, especially during periods of infrequent use.

Data Point: A study by the University of Nebraska-Lincoln found that using fuel stabilizer can extend the shelf life of gasoline by up to 12 months.

Call to Action: If you suspect your fuel is the problem, drain it, replace the fuel filter, and mix fresh fuel with a fuel stabilizer. This simple step can often solve starting problems and improve engine performance. Consider purchasing a fuel stabilizer like STA-BIL through our affiliate link to keep your fuel fresh.

2. Spark Problems: Igniting the Fire

The Problem: A faulty spark plug or ignition system can prevent the engine from firing. The spark plug creates the spark that ignites the fuel-air mixture in the cylinder. If the spark plug is fouled, cracked, or improperly gapped, it may not produce a strong enough spark to ignite the mixture. Similarly, a faulty ignition coil or wiring can prevent the spark plug from receiving the necessary voltage.

Why it Matters: The spark plug is a critical component of the ignition system. A weak or nonexistent spark can result in hard starting, poor engine performance, and increased emissions.

My Experience: I once spent hours troubleshooting a Stihl MS 250 that wouldn’t start, only to discover that the spark plug was the culprit. The spark plug looked fine at first glance, but upon closer inspection, I noticed a hairline crack in the ceramic insulator. Replacing the spark plug with a new one solved the problem immediately.

Troubleshooting Steps:

1. Access the Spark Plug:
   • Locate the spark plug on the side of the engine. It’s usually covered by a rubber boot.
   • Pull the rubber boot off the spark plug.
2. Remove the Spark Plug:
   • Use a spark plug wrench (typically 19mm) to loosen and remove the spark plug.
   • Turn the wrench counterclockwise to loosen the spark plug.
3. Inspect the Spark Plug:
   • Electrode: Check the electrode for wear, carbon buildup, or damage. The electrode should be clean and have a sharp edge.
   • Insulator: Inspect the ceramic insulator for cracks or chips. A cracked insulator can cause the spark to leak to ground.
   • Color: The color of the spark plug can provide clues about the engine’s condition. A light tan color indicates normal operation. A black, sooty color indicates a rich fuel mixture. A white or gray color indicates a lean fuel mixture.
4. Clean or Replace the Spark Plug:
   • If the spark plug is fouled with carbon buildup, you can try cleaning it with a wire brush or spark plug cleaner.
   • However, if the spark plug is cracked or damaged, it should be replaced.
   • The recommended spark plug for Stihl MS 250 is NGK BPMR7A or Bosch WSR6F.
5. Gap the Spark Plug:
   • Use a spark plug gapping tool to set the gap between the electrode and the ground electrode.
   • The correct spark plug gap for Stihl MS 250 is 0.020 inches (0.5 mm).
6. Test for Spark:
   • Reattach the spark plug to the rubber boot.
   • Hold the spark plug against the engine block, making sure the metal part of the spark plug is touching metal on the engine.
   • Pull the starter cord.
   • Observe the spark plug electrode. You should see a bright, blue spark jumping across the gap.
   • If there is no spark, or if the spark is weak or yellow, the ignition system may be faulty.
7. Check the Ignition Coil:
   • If the spark plug is good but there is no spark, the ignition coil may be the problem.
   • The ignition coil is responsible for generating the high-voltage electricity needed to create the spark.
   • Use a multimeter to test the ignition coil’s resistance.
   • Consult the Stihl MS 250 service manual for the correct resistance values.
   • If the ignition coil’s resistance is outside the specified range, it should be replaced.

Pro Tip: Keep a spare spark plug on hand. Spark plugs are inexpensive and easy to replace, and having a spare can save you a lot of downtime in the field.

Data Point: According to NGK Spark Plugs, a fouled spark plug can reduce fuel efficiency by up to 30%.

Call to Action: Inspect your spark plug regularly and replace it every 100 hours of operation or once a year, whichever comes first. If you suspect a problem with your ignition system, test the spark plug and ignition coil. Consider purchasing a spark plug and a spark plug wrench through our affiliate link to keep your saw running smoothly.

3. Carburetor Problems: Fine-Tuning the Fuel-Air Mix

The Problem: A clogged or misadjusted carburetor can disrupt the fuel-air mixture, preventing the engine from starting or causing it to run poorly. The carburetor is responsible for mixing the correct amount of fuel with air to create a combustible mixture. If the carburetor is clogged with dirt, debris, or gum, it may not be able to deliver the proper fuel-air mixture. Similarly, if the carburetor is misadjusted, the engine may run too lean (too much air) or too rich (too much fuel).

Why it Matters: The carburetor is a crucial component of the engine’s fuel system. A properly functioning carburetor is essential for optimal engine performance, fuel efficiency, and emissions control.

My Experience: I once bought a used Stihl MS 250 that ran terribly. It was hard to start, idled roughly, and lacked power. I initially suspected a major engine problem, but after cleaning and adjusting the carburetor, the saw ran like new. The previous owner had likely never cleaned or adjusted the carburetor, and it was severely clogged with dirt and gum.

Troubleshooting Steps:

1. Check the Carburetor Settings:
   • The carburetor has three adjustment screws: the low-speed (L) screw, the high-speed (H) screw, and the idle speed (LA) screw.
   • The L and H screws control the fuel-air mixture at low and high engine speeds, respectively.
   • The LA screw controls the engine’s idle speed.
   • Consult the Stihl MS 250 service manual for the correct carburetor settings.
   • As a starting point, turn both the L and H screws clockwise until they are lightly seated, then back them out 1 to 1.5 turns.
   • Adjust the LA screw until the engine idles smoothly without stalling.
2. Clean the Carburetor:
   • If the carburetor is clogged with dirt or gum, it may need to be cleaned.
   • Remove the air filter and the carburetor cover.
   • Carefully disconnect the fuel lines and the throttle linkage from the carburetor.
   • Remove the carburetor from the engine.
   • Disassemble the carburetor, taking note of the location of all the parts.
   • Clean the carburetor body, jets, and passages with carburetor cleaner.
   • Use compressed air to blow out any remaining debris.
   • Reassemble the carburetor, making sure all the parts are properly seated.
   • Reinstall the carburetor on the engine.
   • Reconnect the fuel lines and the throttle linkage.
   • Adjust the carburetor settings as described above.
3. Check the Fuel Lines:
   • Inspect the fuel lines for cracks, leaks, or kinks.
   • Replace any damaged fuel lines.
4. Check the Impulse Line:
   • The impulse line connects the carburetor to the engine crankcase.
   • The impulse line provides the vacuum signal that operates the carburetor’s fuel pump.
   • Inspect the impulse line for cracks or leaks.
   • Replace any damaged impulse lines.

Pro Tip: Use a carburetor rebuild kit when cleaning the carburetor. A carburetor rebuild kit includes all the necessary gaskets, seals, and O-rings to ensure a proper seal.

Data Point: According to the EPA, a misadjusted carburetor can increase emissions by up to 50%.

Case Study: A local logging company was experiencing frequent carburetor problems with their Stihl MS 250 chainsaws. After analyzing the problem, I discovered that the company was using low-quality fuel and not performing regular carburetor maintenance. I recommended switching to a higher-quality fuel and implementing a regular carburetor cleaning schedule. As a result, the company significantly reduced their carburetor problems and improved their chainsaw performance.

Call to Action: Clean and adjust your carburetor regularly. If you’re not comfortable cleaning the carburetor yourself, take it to a qualified technician. Consider purchasing a carburetor cleaner and a carburetor rebuild kit through our affiliate link to keep your carburetor running smoothly.

4. Air Filter Problems: Letting the Engine Breathe

The Problem: A dirty air filter can restrict airflow and choke the engine, preventing it from starting or causing it to run poorly. The air filter prevents dirt, dust, and debris from entering the engine. When the air filter becomes clogged, it restricts the amount of air that can enter the engine, resulting in a lean fuel mixture.

Why it Matters: A clean air filter is essential for proper engine performance and longevity. A restricted air filter can reduce engine power, increase fuel consumption, and cause premature engine wear.

My Experience: I once had a Stihl MS 250 that was running sluggishly and lacked power. I initially suspected a fuel or ignition problem, but after checking the air filter, I discovered that it was completely clogged with sawdust and dirt. Cleaning the air filter restored the engine’s power and performance.

Troubleshooting Steps:

1. Access the Air Filter:
   • Locate the air filter cover on the top or side of the engine.
   • Remove the air filter cover.
2. Inspect the Air Filter:
   • Remove the air filter from the engine.
   • Inspect the air filter for dirt, dust, and debris.
   • Hold the air filter up to the light. If you can’t see light through the filter, it’s likely clogged.
3. Clean or Replace the Air Filter:
   • If the air filter is only slightly dirty, you can try cleaning it.
   • Tap the air filter against a hard surface to remove loose dirt and debris.
   • Wash the air filter with warm, soapy water.
   • Rinse the air filter thoroughly with clean water.
   • Allow the air filter to air dry completely before reinstalling it.
   • If the air filter is heavily soiled or damaged, it should be replaced.
   • The recommended air filter for Stihl MS 250 is Stihl part number 1123-120-1613.
4. Reinstall the Air Filter:
   • Reinstall the air filter in the engine.
   • Make sure the air filter is properly seated.
   • Reinstall the air filter cover.

Pro Tip: Clean your air filter regularly, especially when working in dusty or dirty conditions. I recommend cleaning the air filter after every 10 hours of operation or more frequently if needed.

Data Point: According to the USDA Forest Service, a clogged air filter can reduce engine power by up to 20%.

Call to Action: Inspect and clean your air filter regularly. If the air filter is heavily soiled or damaged, replace it. Consider purchasing an air filter cleaner and a spare air filter through our affiliate link to keep your engine breathing freely.

5. Compression Issues: The Heart of the Engine

The Problem: Low compression can indicate serious engine damage, such as worn piston rings, a damaged cylinder, or leaky valves. Compression is the measure of how tightly the piston compresses the fuel-air mixture in the cylinder. Low compression means that the fuel-air mixture is not being compressed enough, which can prevent the engine from starting or cause it to run poorly.

Why it Matters: Compression is essential for proper engine operation. Low compression can lead to hard starting, poor engine performance, increased fuel consumption, and increased emissions.

My Experience: I once had a Stihl MS 250 that gradually lost power over time. It eventually became very difficult to start and ran very poorly. After checking the compression, I discovered that it was significantly lower than the manufacturer’s specification. Upon further inspection, I found that the piston rings were worn and the cylinder was scored. The engine needed a complete overhaul.

Troubleshooting Steps:

1. Check the Compression:
   • Remove the spark plug.
   • Insert a compression tester into the spark plug hole.
   • Pull the starter cord several times to build up pressure in the cylinder.
   • Read the compression gauge.
   • The minimum compression for Stihl MS 250 is typically around 120 PSI.
   • If the compression is below 120 PSI, the engine may have a compression problem.
2. Perform a Leak-Down Test:
   • A leak-down test can help you pinpoint the source of the compression leak.
   • Insert a leak-down tester into the spark plug hole.
   • Apply compressed air to the cylinder.
   • Listen for air leaking from the exhaust pipe, the carburetor, or the crankcase.
   • Air leaking from the exhaust pipe indicates a leaky exhaust valve.
   • Air leaking from the carburetor indicates a leaky intake valve.
   • Air leaking from the crankcase indicates worn piston rings or a damaged cylinder.
3. Inspect the Cylinder and Piston:
   • If the compression test or leak-down test indicates a compression problem, you may need to inspect the cylinder and piston.
   • Remove the cylinder head.
   • Inspect the cylinder walls for scoring, scratches, or damage.
   • Inspect the piston for wear, cracks, or damage.
   • Inspect the piston rings for wear or breakage.
4. Repair or Replace Damaged Components:
   • If the cylinder is scored or damaged, it may need to be honed or replaced.
   • If the piston is worn or damaged, it should be replaced.
   • If the piston rings are worn or broken, they should be replaced.

Pro Tip: Use a high-quality 2-cycle oil to lubricate the engine and prevent premature wear. I recommend using Stihl HP Ultra oil or a similar synthetic 2-cycle oil.

Data Point: According to a study by the American Society of Agricultural and Biological Engineers (ASABE), low compression can reduce engine power by up to 40%.

Case Study: A small firewood producer was experiencing frequent engine failures with their Stihl MS 250 chainsaws. After analyzing the problem, I discovered that the company was not performing regular engine maintenance and was using low-quality 2-cycle oil. I recommended implementing a regular engine maintenance schedule and switching to a higher-quality 2-cycle oil. As a result, the company significantly reduced their engine failures and improved their chainsaw reliability.

Call to Action: Check your engine’s compression regularly. If you suspect a compression problem, perform a leak-down test and inspect the cylinder and piston. If you’re not comfortable performing these tasks yourself, take the saw to a qualified technician. Consider purchasing a compression tester and a leak-down tester through our affiliate link to diagnose compression problems.

Preventative Maintenance: Keeping Your MS 250 Healthy

Preventative maintenance is the key to keeping your Stihl MS 250 running smoothly and avoiding starting problems. By performing regular maintenance tasks, you can catch potential problems early and prevent them from escalating into major repairs.

Here are some essential preventative maintenance tasks for your Stihl MS 250:

• Clean the Air Filter Regularly: Clean the air filter after every 10 hours of operation or more frequently if needed.
• Inspect the Spark Plug Regularly: Inspect the spark plug for wear, carbon buildup, or damage. Replace the spark plug every 100 hours of operation or once a year, whichever comes first.
• Clean the Carburetor Regularly: Clean the carburetor every 6 months or more frequently if needed.
• Use Fresh Fuel: Use fresh, properly mixed fuel. Dispose of old fuel properly.
• Sharpen the Chain Regularly: A sharp chain cuts more efficiently and reduces strain on the engine.
• Check the Chain Tension Regularly: Proper chain tension is essential for safe and efficient operation.
• Lubricate the Chain Regularly: Use a high-quality bar and chain oil to lubricate the chain and prevent wear.
• Inspect the Bar Regularly: Check the bar for wear, damage, or burrs.
• Clean the Cooling Fins Regularly: Keep the cooling fins on the cylinder clean to prevent overheating.
• Store the Chainsaw Properly: Store the chainsaw in a dry, protected location. Drain the fuel tank before storing the chainsaw for extended periods.

Conclusion: Back to the Woods

Troubleshooting a Stihl MS 250 that won’t start can be frustrating, but by following these steps, you can diagnose and fix many common problems. Remember to start with the basics, such as checking the fuel, spark, and air filter. If those components are in good condition, move on to more complex issues, such as carburetor problems or compression issues.

With a little patience and persistence, you can get your Stihl MS 250 running smoothly again and get back to the woods. And remember, preventative maintenance is the key to keeping your saw healthy and avoiding future starting problems.

Now, get out there and make some sawdust! And if you need any of the tools or supplies mentioned in this article, be sure to check out our affiliate links. Happy cutting!

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