Stihl MS 150 TC Troubleshooting (5 Pro Fixes for Rev Issues)

The Stihl MS 150 TC. Just the name whispers power, precision, and… potential problems. Let me tell you, I’ve wrestled with enough MS 150 TCs to fill a small logging truck. And more often than not, the culprit behind a stalled operation, a frustrated user, and wasted time? Rev issues. That frustrating sputter, the hesitation, the complete lack of oomph when you need it most. It can drive a woodcutter to madness.

But don’t throw your gloves in just yet. This guide is your lifeline. I’ve poured years of firsthand experience, countless hours of troubleshooting, and a healthy dose of chainsaw whisperer magic into these pages. This isn’t just another generic troubleshooting guide. This is the real deal, the gritty, hands-on knowledge you need to breathe life back into your MS 150 TC and get it roaring again. We’re going to dive deep into the heart of those rev problems, diagnose them with precision, and administer five pro-level fixes that will have your saw singing a sweet tune in no time.

Stihl MS 150 TC Troubleshooting: 5 Pro Fixes for Rev Issues

Before we get our hands dirty, it’s important to understand the MS 150 TC. This top-handle chainsaw is a beast, specifically designed for pruning and tree care by trained professionals. Its lightweight design (around 6.3 lbs) and maneuverability make it ideal for working in elevated positions. But that also means it’s often subjected to demanding conditions, requiring meticulous maintenance and a keen eye for potential problems.

1. Fuel System Follies: The Lifeline to Performance

The fuel system is the heart of any engine. If it’s clogged, contaminated, or malfunctioning, your chainsaw simply won’t perform. This is the most common area I see issues arise.

Symptoms:

• Engine starts but stalls immediately.
• Engine runs rough or hesitates under load.
• Engine is hard to start.
• Loss of power during cutting.

Pro Fix: A Deep Dive into Fuel System Components

I start with the basics and move up in complexity. Here’s the systematic approach I’ve perfected over the years:

1. Fuel Quality Check: Always begin with fresh fuel. I can’t stress this enough. Ethanol-blended fuels are a major culprit. Ethanol attracts moisture, leading to phase separation and gum formation, especially during storage. I always recommend using ethanol-free fuel or adding a fuel stabilizer like Stihl’s MotoMix when storing the saw for more than a month.

   • Data Point: Ethanol blends can degrade in as little as 30 days, leading to engine damage.
   • Practical Tip: Always drain the fuel tank before storing the saw for extended periods.
   • Fuel Mix Ratio: Stihl recommends a 50:1 fuel-to-oil ratio. Using the wrong ratio can lead to lubrication problems and engine damage. I personally use a pre-mixed 50:1 fuel like Stihl MotoMix, as it ensures the correct ratio and contains fuel stabilizers.

   • Fuel Filter Inspection & Replacement: The fuel filter is your first line of defense against debris. A clogged filter starves the engine.

   • Procedure: Locate the fuel filter inside the fuel tank (attached to the fuel line). Use a small hook or wire to carefully pull it out.
   • Inspection: Examine the filter for dirt, debris, or damage. If it’s dirty, try cleaning it with carburetor cleaner. If it’s damaged or heavily clogged, replace it.
   • Replacement: Install a new fuel filter, ensuring it’s securely attached to the fuel line. I keep a stock of these on hand; they’re cheap insurance.
   • Technical Requirement: Use the correct fuel filter specified for the Stihl MS 150 TC. Using the wrong filter can restrict fuel flow and damage the engine.

   • Fuel Line Examination: Fuel lines can crack, harden, or become porous over time, leading to air leaks and fuel starvation.

   • Procedure: Inspect the fuel lines for cracks, leaks, or kinks. Pay close attention to the areas where the lines connect to the fuel tank, carburetor, and fuel filter.

   • Replacement: If you find any damage, replace the fuel lines. This is a common issue on older saws, and replacing the lines is a relatively simple and inexpensive fix.
   • Technical Requirement: Use fuel lines that are resistant to gasoline and oil. The inside diameter of the fuel line should match the original specifications (typically 3/32″ or 2.5mm).

   • Carburetor Cleaning & Adjustment: The carburetor mixes air and fuel to create the perfect combustion mixture. A dirty or misadjusted carburetor can cause a range of problems.

   • Procedure: This is where things get a bit more technical. First, locate the carburetor. It’s usually located behind the air filter.
   • Cleaning: Use carburetor cleaner to thoroughly clean the carburetor. Pay close attention to the jets and passages. You may need to disassemble the carburetor to clean it properly. I recommend watching a few YouTube videos before attempting this, as it can be tricky.
   • Adjustment: Adjust the carburetor according to the manufacturer’s specifications. The MS 150 TC typically has two adjustment screws: the “L” screw (low-speed) and the “H” screw (high-speed).
     • Initial Settings: Start with the factory settings, which are usually listed in the owner’s manual. As a general rule, turn both screws clockwise until they are lightly seated, then back them out the specified number of turns.
     • Fine-Tuning: Start the engine and let it warm up. Adjust the “L” screw until the engine idles smoothly without stalling. Then, adjust the “H” screw until the engine reaches its maximum RPM without bogging down. Use a tachometer to ensure you don’t exceed the maximum RPM.
     • Data Point: The optimal idle speed for the MS 150 TC is around 2,800 RPM. The maximum RPM is around 12,500 RPM.
     • Technical Requirement: Use a non-marring screwdriver to adjust the carburetor screws. Overtightening the screws can damage the carburetor.
   • Case Study: I once had a client who brought in an MS 150 TC that wouldn’t start. He’d been using ethanol-blended fuel and storing the saw for long periods without draining the tank. The fuel filter was completely clogged with a gummy residue. After replacing the fuel filter and cleaning the carburetor, the saw fired right up. He learned his lesson about fuel quality!

Common Mistakes to Avoid:

• Using the wrong fuel mix ratio.
• Using old or contaminated fuel.
• Over-tightening the carburetor screws.
• Forgetting to replace the fuel filter.

2. Ignition Issues: Sparking the Solution

If the fuel system is functioning correctly, the next suspect is the ignition system. Without a strong spark, combustion simply cannot occur.

Symptoms:

• Engine won’t start at all.
• Engine is difficult to start.
• Engine runs intermittently.

Pro Fix: Tracing the Spark

1. Spark Plug Inspection & Replacement: The spark plug is the heart of the ignition system. A fouled, cracked, or worn spark plug can prevent the engine from starting.

   • Procedure: Remove the spark plug using a spark plug wrench.
   • Inspection: Examine the spark plug for cracks, carbon buildup, or damage.
   • Cleaning: If the spark plug is simply fouled with carbon, try cleaning it with a wire brush or spark plug cleaner.
   • Replacement: If the spark plug is damaged or worn, replace it with a new one. I recommend replacing the spark plug annually, even if it looks okay.
   • Technical Requirement: Use the correct spark plug specified for the Stihl MS 150 TC (typically an NGK CMR6H). Using the wrong spark plug can damage the engine.
   • Spark Plug Gap: The spark plug gap is the distance between the center electrode and the ground electrode. The correct spark plug gap for the MS 150 TC is typically 0.020 inches (0.5mm). Use a spark plug gap tool to ensure the gap is correct.

   • Ignition Coil Testing: The ignition coil generates the high-voltage spark that ignites the fuel mixture. A faulty ignition coil can prevent the engine from starting.

   • Procedure: Use a multimeter to test the ignition coil. This requires some electrical knowledge. If you’re not comfortable with this, take the saw to a qualified technician.

   • Testing: Disconnect the spark plug wire from the spark plug. Set the multimeter to the resistance setting. Connect the multimeter probes to the spark plug wire terminal and the engine ground. The resistance should be within the manufacturer’s specifications.
   • Replacement: If the ignition coil is faulty, replace it.

   • Spark Test: Visually confirm the presence of a spark.

   • Procedure: Remove the spark plug and reattach it to the spark plug wire. Hold the spark plug against the engine cylinder head (grounding it). Pull the starter rope. You should see a strong, blue spark jumping across the spark plug gap.

   • No Spark: If you don’t see a spark, the ignition coil may be faulty, or there may be a problem with the wiring.
   • Weak Spark: If you see a weak, yellow spark, the ignition coil may be weak, or the spark plug may be fouled.

Common Mistakes to Avoid:

• Using the wrong spark plug.
• Not gapping the spark plug correctly.
• Damaging the spark plug during installation.

3. Air Intake Obstructions: Letting the Engine Breathe

A clean air filter is crucial for proper engine performance. A clogged air filter restricts airflow, leading to a rich fuel mixture and reduced power.

Symptoms:

• Engine runs rough or hesitates under load.
• Engine lacks power.
• Engine is hard to start.

Pro Fix: Clearing the Airways

1. Air Filter Inspection & Cleaning/Replacement: This is the simplest and most often overlooked step.

   • Procedure: Locate the air filter (usually under a cover on top of the engine).
   • Inspection: Examine the air filter for dirt, debris, or damage.
   • Cleaning: If the air filter is simply dirty, try cleaning it with compressed air or warm soapy water. Allow the filter to dry completely before reinstalling it.
   • Replacement: If the air filter is damaged or heavily clogged, replace it with a new one. I recommend replacing the air filter every season, or more often if you’re working in dusty conditions.
   • Technical Requirement: Use the correct air filter specified for the Stihl MS 150 TC. Using the wrong air filter can restrict airflow and damage the engine.

   • Intake Manifold Inspection: Inspect the intake manifold for cracks or leaks. Air leaks can cause the engine to run lean.

   • Procedure: Visually inspect the intake manifold for cracks or damage.
   • Testing: Use carburetor cleaner to spray around the intake manifold while the engine is running. If the engine speed changes, there may be a leak.
   • Replacement: If you find any cracks or leaks, replace the intake manifold.

Common Mistakes to Avoid:

• Reinstalling a wet air filter.
• Using the wrong air filter.
• Not cleaning the air filter regularly.

4. Exhaust System Blockages: Letting the Engine Exhale

Just as important as getting air in is getting exhaust out. A clogged exhaust system restricts exhaust flow, leading to reduced power and overheating.

Symptoms:

• Engine lacks power.
• Engine overheats.
• Engine is hard to start.

Pro Fix: Freeing the Flow

1. Spark Arrestor Screen Inspection & Cleaning: The spark arrestor screen prevents sparks from exiting the exhaust system. A clogged spark arrestor screen restricts exhaust flow.

   • Procedure: Locate the spark arrestor screen on the muffler. Remove the screen using a small screwdriver or pliers.
   • Inspection: Examine the screen for carbon buildup or damage.
   • Cleaning: Clean the screen with a wire brush or carburetor cleaner.
   • Replacement: If the screen is damaged, replace it. I clean mine every 25 hours of use.
   • Technical Requirement: Use the correct spark arrestor screen specified for the Stihl MS 150 TC.

   • Muffler Inspection: Inspect the muffler for damage or blockages. A damaged or blocked muffler can restrict exhaust flow.

   • Procedure: Visually inspect the muffler for cracks, dents, or other damage.

   • Testing: Use a wire or small tool to probe the muffler for blockages.
   • Replacement: If you find any damage or blockages, replace the muffler.

Common Mistakes to Avoid:

• Forgetting to clean the spark arrestor screen.
• Damaging the spark arrestor screen during cleaning.
• Using the wrong spark arrestor screen.

5. Mechanical Mayhem: The Internal Culprits

Sometimes, the problem lies deeper within the engine. While less common, mechanical issues can cause significant rev problems.

Symptoms:

• Engine makes unusual noises.
• Engine lacks compression.
• Engine runs very rough.

Pro Fix: Investigating the Internals

Note: These repairs often require specialized tools and knowledge. If you’re not comfortable with these procedures, take the saw to a qualified technician.

1. Compression Test: A compression test measures the pressure inside the engine cylinder. Low compression indicates a problem with the piston rings, cylinder, or valves.

   • Procedure: Remove the spark plug. Install a compression tester into the spark plug hole. Pull the starter rope several times.
   • Reading: The compression reading should be within the manufacturer’s specifications (typically around 120-150 PSI for the MS 150 TC).
   • Low Compression: If the compression is low, there may be a problem with the piston rings, cylinder, or valves.

   • Piston & Cylinder Inspection: Inspect the piston and cylinder for scoring, scratches, or other damage.

   • Procedure: Remove the cylinder head. Inspect the piston and cylinder for damage.
   • Replacement: If you find any damage, replace the piston and cylinder.

   • Flywheel Key Shear: The flywheel key aligns the flywheel with the crankshaft. If the key shears, the engine timing will be off, causing the engine to run poorly.

   • Procedure: Remove the flywheel. Inspect the flywheel key for damage.

   • Replacement: If the key is sheared, replace it.

Common Mistakes to Avoid:

• Not using the correct tools.
• Damaging the engine during disassembly.
• Not following the manufacturer’s instructions.

Preventative Maintenance: The Key to Longevity

The best way to avoid rev issues is to perform regular preventative maintenance.

• Clean the air filter regularly.
• Replace the fuel filter annually.
• Replace the spark plug annually.
• Clean the spark arrestor screen regularly.
• Use fresh, high-quality fuel.
• Store the saw properly.
• Follow the manufacturer’s maintenance schedule.

Final Thoughts

Troubleshooting rev issues on a Stihl MS 150 TC can be challenging, but by following these pro-level fixes and practicing preventative maintenance, you can keep your saw running smoothly for years to come. Remember, safety is paramount. Always wear appropriate safety gear and follow the manufacturer’s instructions. And when in doubt, consult a qualified technician. Now go forth and conquer those cutting tasks!

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