MS 170 Carburetor Tune Tips (5 Pro Hacks for Smoother Cuts)

As the crisp autumn air begins to bite, and the leaves crunch underfoot, my thoughts naturally turn to firewood. For many of us, that means dusting off the trusty chainsaw – in my case, a reliable Stihl MS 170. This little workhorse has seen me through countless cords of wood, but like any machine, it needs a little TLC to keep running smoothly. A properly tuned carburetor is crucial for efficient cutting, especially when dealing with tougher hardwoods. Over the years, I’ve learned a few tricks to optimize the MS 170’s carb. I’m here to share my top five pro hacks for smoother cuts and a more enjoyable wood-splitting season.

MS 170 Carburetor Tune Tips (5 Pro Hacks for Smoother Cuts)

The Stihl MS 170 is a popular choice for homeowners and light-duty users due to its affordability and ease of use. However, its performance can suffer if the carburetor isn’t properly tuned. A poorly tuned carb can lead to issues like difficult starting, poor idling, stalling during cuts, and reduced power. These problems not only make woodcutting more frustrating but can also damage the engine over time. These tips are applicable to other similar models, but always check your owner’s manual.

Hack #1: Master the Basics – Understanding Your MS 170 Carburetor

Before diving into adjustments, it’s important to understand the basics of how the MS 170 carburetor works. The carburetor’s primary function is to mix air and fuel in the correct ratio to create a combustible mixture for the engine. The MS 170 typically features a simple carburetor with three adjustment screws:

• LA (Idle Speed Adjustment): Controls the engine’s idling speed, preventing it from stalling when the throttle is released.
• H (High-Speed Adjustment): Regulates the fuel flow at high engine speeds, affecting the saw’s power and performance during cuts.
• L (Low-Speed Adjustment): Controls the fuel flow at low engine speeds, influencing starting and idling characteristics.

Understanding the function of each screw is essential for making informed adjustments. For example, if your saw stalls frequently when idling, adjusting the LA screw might be the solution.

My Experience: I remember one particularly cold winter day when my MS 170 refused to idle. After checking the fuel lines and spark plug, I realized the LA screw was the culprit. A slight adjustment, and the saw purred like a kitten.

Data Point: According to Stihl’s technical documentation, the factory setting for the H and L screws is typically one full turn out from the fully closed position. However, this is a starting point and may need to be adjusted based on your specific conditions.

Actionable Tip: Familiarize yourself with the location of these screws on your MS 170. Refer to your owner’s manual for a diagram.

Takeaway: Understanding the basic function of each adjustment screw is the foundation for effective carburetor tuning.

Hack #2: The Tachometer Trick – Precision Tuning for Peak Performance

While you can tune a carburetor by ear, using a tachometer provides a much more precise and reliable method. A tachometer measures the engine’s RPM (revolutions per minute), allowing you to fine-tune the H screw for optimal high-speed performance without risking engine damage.

Here’s how to use a tachometer for carburetor tuning:

1. Warm-up the Engine: Start the MS 170 and let it run for a few minutes to reach operating temperature.
2. Attach the Tachometer: Connect the tachometer according to its instructions. Most tachometers use an inductive pickup that clamps onto the spark plug wire.
3. Locate the Maximum RPM Specification: Refer to your MS 170’s owner’s manual for the recommended maximum RPM. Typically, it’s around 12,500-13,500 RPM.
4. Adjust the H Screw: With the engine running at full throttle, slowly adjust the H screw. Turning it clockwise (in) leans the mixture, increasing RPM. Turning it counter-clockwise (out) richens the mixture, decreasing RPM.
5. Aim for the Target RPM: Adjust the H screw until the tachometer reads the recommended maximum RPM. It’s better to err on the side of a slightly richer mixture (lower RPM) than a lean mixture, which can damage the engine.
6. Listen for Four-Stroking: While running at full throttle, listen for a “four-stroking” sound. This is a sputtering or gurgling sound that indicates a slightly rich mixture. If you hear four-stroking, lean the mixture slightly (turn the H screw clockwise) until it disappears.

My Experience: I once tuned an MS 170 without a tachometer, relying solely on my ear. While it seemed to run okay, I later discovered I was running it too lean, which caused premature wear on the piston and cylinder. Lesson learned – a tachometer is a worthwhile investment.

Data Point: Running an engine too lean (too much air, not enough fuel) can increase engine temperature and lead to piston seizure. Conversely, running too rich (too much fuel, not enough air) can cause excessive carbon buildup and reduced power.

Actionable Tip: Invest in a digital tachometer specifically designed for small engines. They are relatively inexpensive and can save you from costly repairs down the road.

Takeaway: Using a tachometer allows you to fine-tune the H screw for optimal performance and engine longevity.

Hack #3: The Paper Bag Test – Fine-Tuning the L Screw for Smooth Acceleration

The L screw controls the fuel mixture at low engine speeds, and it plays a crucial role in the saw’s ability to accelerate smoothly. A properly adjusted L screw ensures quick throttle response and prevents the engine from bogging down when you apply the throttle. The “paper bag test” is a simple yet effective way to fine-tune the L screw.

Here’s how to perform the paper bag test:

1. Warm-up the Engine: Start the MS 170 and let it run for a few minutes to reach operating temperature.
2. Find a Clean Piece of Paper: A brown paper bag works well for this test.
3. Hold the Paper Near the Air Filter: Hold the paper a few inches away from the air filter while the engine is idling.
4. Observe the Engine’s Response: If the engine’s RPM increases slightly when you hold the paper near the air filter, the L screw is likely set too lean. If the engine’s RPM decreases or stalls, the L screw is likely set too rich.
5. Adjust the L Screw:
   • If the engine speeds up (lean): Turn the L screw counter-clockwise (out) in small increments (1/8 turn at a time) until the engine runs smoothly and the RPM doesn’t change significantly when you hold the paper near the air filter.
   • If the engine slows down or stalls (rich): Turn the L screw clockwise (in) in small increments (1/8 turn at a time) until the engine runs smoothly and the RPM doesn’t change significantly when you hold the paper near the air filter.
6. Test the Throttle Response: After adjusting the L screw, quickly apply full throttle. The engine should accelerate smoothly without bogging down or hesitating. If it hesitates, continue to fine-tune the L screw until the throttle response is crisp and immediate.

My Experience: I used to struggle with my MS 170 bogging down when I tried to cut through thicker logs. After performing the paper bag test and adjusting the L screw, the throttle response improved dramatically, and I was able to cut through the logs with ease.

Data Point: A lean low-speed mixture can cause the engine to hesitate or stall when you apply the throttle, while a rich low-speed mixture can cause excessive smoke and poor fuel economy.

Actionable Tip: Make small adjustments to the L screw and test the throttle response after each adjustment. It’s better to make incremental changes than to drastically alter the setting.

Takeaway: The paper bag test is a simple and effective way to fine-tune the L screw for smooth acceleration and optimal throttle response.

Hack #4: Idle Speed Perfection – Setting the LA Screw for Stall-Free Operation

The LA screw controls the engine’s idling speed, and setting it correctly is crucial for preventing the saw from stalling when the throttle is released. The ideal idling speed is high enough to keep the engine running smoothly but low enough to prevent the chain from spinning.

Here’s how to set the LA screw:

1. Warm-up the Engine: Start the MS 170 and let it run for a few minutes to reach operating temperature.
2. Locate the LA Screw: The LA screw is typically located near the throttle linkage.
3. Adjust the LA Screw:
   • If the engine stalls: Turn the LA screw clockwise (in) to increase the idling speed.
   • If the chain spins at idle: Turn the LA screw counter-clockwise (out) to decrease the idling speed.
4. Fine-Tune the Idle Speed: Adjust the LA screw until the engine idles smoothly without stalling and the chain does not spin.
5. Test the Idle Speed: Let the saw idle for a minute or two to ensure it doesn’t stall. If it stalls, increase the idle speed slightly.

My Experience: I once had an MS 170 that would stall every time I released the throttle. After adjusting the LA screw, the problem was solved, and the saw idled perfectly.

Data Point: The ideal idling speed for the MS 170 is typically around 2,800-3,200 RPM. However, it’s best to adjust the LA screw until the engine idles smoothly without the chain spinning.

Actionable Tip: After adjusting the LA screw, check the chain to ensure it’s not spinning at idle. If it is, decrease the idle speed slightly.

Takeaway: Setting the LA screw correctly is essential for stall-free operation and a smooth cutting experience.

Hack #5: The Complete Carburetor Cleaning – A Preventative Measure for Long-Term Performance

Even with careful tuning, the carburetor can become clogged with dirt, debris, and old fuel over time. This can lead to poor performance, difficult starting, and even engine damage. Regularly cleaning the carburetor is a preventative measure that can help ensure long-term performance and reliability.

Here’s how to clean the MS 170 carburetor:

1. Gather Your Supplies: You’ll need a carburetor cleaner, a small screwdriver set, compressed air, and a clean workspace.
2. Remove the Air Filter and Carburetor Cover: Remove the air filter and the carburetor cover to expose the carburetor.
3. Disconnect the Fuel Lines and Throttle Linkage: Carefully disconnect the fuel lines and throttle linkage from the carburetor. Take pictures as you disassemble to assist with reassembly.
4. Remove the Carburetor: Remove the carburetor from the engine.
5. Disassemble the Carburetor: Disassemble the carburetor carefully, noting the location of each part. Pay attention to the gaskets and diaphragms, as they can be easily damaged.
6. Clean the Carburetor Components: Spray all the carburetor components with carburetor cleaner and use compressed air to blow out any dirt or debris. Pay particular attention to the jets and passages.
7. Inspect the Gaskets and Diaphragms: Inspect the gaskets and diaphragms for any signs of damage or wear. Replace them if necessary.
8. Reassemble the Carburetor: Reassemble the carburetor carefully, ensuring that all the parts are in the correct location.
9. Reinstall the Carburetor: Reinstall the carburetor on the engine and reconnect the fuel lines and throttle linkage.
10. Adjust the Carburetor: After reinstalling the carburetor, adjust the H, L, and LA screws according to the steps outlined in the previous sections.

My Experience: I neglected to clean the carburetor on my MS 170 for several years, and it eventually became so clogged that the saw wouldn’t start. After cleaning the carburetor, the saw ran like new.

Data Point: Carburetor cleaner contains harsh chemicals, so be sure to wear gloves and eye protection when using it.

Actionable Tip: Consider purchasing a carburetor rebuild kit, which includes new gaskets, diaphragms, and other essential parts.

Takeaway: Regularly cleaning the carburetor is a preventative measure that can help ensure long-term performance and reliability.

By mastering these five pro hacks, you can keep your Stihl MS 170 running smoothly and efficiently for years to come. Remember to always prioritize safety and consult your owner’s manual for specific instructions and recommendations. With a little bit of knowledge and effort, you can ensure that your chainsaw is ready to tackle any woodcutting task, making your firewood preparation a breeze. Now, get out there and enjoy the crisp autumn air and the satisfaction of a job well done!

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