If your Stihl MS170 chainsaw is not starting, it can be both frustrating and disruptive to your outdoor projects. Whether you use this popular chainsaw for backyard tasks or professional jobs, reliable starting is crucial. This detailed guide covers common causes of no-start issues, step-by-step troubleshooting, maintenance tips, and answers to frequently asked questions to help you diagnose and fix your Stihl MS170 chainsaw quickly and safely.
Common Causes And Quick Checklist For Stihl MS170 Not Starting
| Cause | Symptoms | Recommended Actions |
|---|---|---|
| Old Or Contaminated Fuel | Chainsaw sputters or won’t fire | Drain and replace with fresh, properly mixed fuel |
| Dirty Air Filter | Engine struggles or won’t start | Clean or replace air filter |
| Flooded Engine | Strong fuel smell, wet spark plug | Dry spark plug, let engine clear for 10 min |
| Spark Plug Issues | No spark, weak ignition | Clean, gap, or replace spark plug |
| Faulty Ignition Coil | No spark at all | Test or replace ignition coil |
| Clogged Carburetor | Engine stalls or won’t start after storage | Clean carburetor, use carb cleaner |
| Blocked Fuel Filter | Irregular fuel flow, engine dies | Replace fuel filter |
| Engine Flooded By Over-Choking | Wet plug, fuel leaks | Follow proper startup routine |
Step-By-Step Troubleshooting Guide
Check The Basics: Fuel, Air, Spark
Begin troubleshooting your Stihl MS170 not starting by checking these core elements:
- Fuel: Ensure you have fresh, properly mixed gasoline (50:1 ratio with high-quality 2-cycle oil).
- Air: Remove the air filter and check for debris or buildup. A dirty filter restricts airflow and can prevent starting.
- Spark: Take out the spark plug, inspect for carbon deposits, and look for a healthy blue spark when grounded and cranked.
Addressing these basic needs often resolves the majority of starting problems.
Inspect And Replace The Spark Plug
A worn, dirty, or wet spark plug is a frequent culprit:
- Remove the spark plug with a socket wrench.
- Check for black soot (carbon fouling), oily residue, or moisture.
- Clean with a wire brush or replace with a fresh NGK BPMR7A or equivalent spark plug, gapped to manufacturer specs.
- If flooded, dry the plug and allow the cylinder to air out before retrying.
Evaluate Fuel System And Carburetor
The fuel system must function smoothly for reliable starting. If the fuel is old (over 30 days) or improperly mixed, drain and refill with new mixture. Examine the following:
- Inspect the fuel filter inside the tank for clogging. Replace if dirty.
- Check fuel lines for cracks or blockages.
- If engine sputters, remove and clean the carburetor using a carb cleaner spray. For thorough cleaning, consider professional service or a rebuild kit.
Clear A Flooded Engine
Flooded engines occur from overuse of the choke or repeated unsuccessful starts. If you detect a strong fuel odor, follow these steps:
- Remove the spark plug and hold the throttle wide open.
- Pull the starter several times to clear fuel vapor.
- Dry the spark plug, reinstall, and attempt starting with reduced or no choke.
Inspect The Air Filter And Muffler
A clogged air filter impedes airflow, while a blocked muffler or spark arrestor screen can trap exhaust:
- Remove the air filter, tap out debris, or replace if heavily soiled.
- Check the muffler for carbon buildup and clean the spark arrestor screen as needed.
Proper airflow is essential for engine combustion.
Assess The Ignition System
If there is still no spark, suspect the ignition coil or switch:
- Test the spark with a known good plug.
- If the ignition coil is faulty, it must be replaced, as it cannot be serviced at home.
- Ensure the on/off switch is properly set to “ON.”
Detailed Breakdown Of Fuel And Air-Related No-Start Issues
Importance Of Fresh Fuel And Correct Mix
Old, stale, or improperly mixed fuel often causes hard starting or failure to start. The Stihl MS170 requires a 50:1 mix of gasoline (minimum 89 octane, ethanol-free is best) and high-quality 2-stroke oil. Always prepare small quantities and never store fuel mixture for more than 30 days.
Dealing With Ethanol Problems
In many parts of the U.S., pump gasoline contains ethanol, which absorbs water and leads to phase separation and corrosion. Opt for ethanol-free gas or add a fuel stabilizer to extend shelf life and minimize carburetor problems.
Clean Or Replace Air Filtration Components
If the air filter is dirty or clogged, remove it and clean it gently with compressed air or soapy water. Replace air filters annually or more often for heavy use or dusty environments.
Starter Assembly And Mechanical Checks
Inspect The Starter Rope And Mechanism
Excessive resistance or a broken starter rope will prevent the engine from turning over. Remove the cover to check for frayed or snapped rope, damaged recoil spring, or stuck mechanism.
Check Chain Brake And Safety Interlocks
The Stihl MS170 includes several safety interlocks (throttle lockout, chain brake). Ensure all are disengaged before starting, as engaged safety features will prevent the chainsaw from firing up.
Carburetor Adjustment For Optimal Starting
Improper carburetor settings can affect fuel delivery and engine starting. The MS170 features three adjustment screws: LA (idle), H (high speed), and L (low speed).
For starting issues:
- Set all screws to factory positions if they have been tampered with (usually L and H to one full turn out from gently seated, LA to keep the chain from moving at idle).
- Fine-tune with the saw running warm; consult your manual for details.
Key Preventative Maintenance To Avoid Starting Problems
Regular Maintenance Schedule
- Fuel: Replace fuel every 30 days; drain for off-season storage.
- Spark Plug: Inspect and clean every 10 hours of use; replace annually.
- Air Filter: Clean every 5-10 hours, replace as needed.
- Bar And Chain: Sharpen regularly, check for proper tension, and keep lubricated.
- Muffler/Spark Arrestor: Clean seasonally or if power drops.
Consistent maintenance keeps your Stihl MS170 running smoothly and reliably.
Cold Weather And Seasonal Starting Tips
How Cold Affects Chainsaw Starting
Cold weather thickens fuel and oil, making starting more difficult. Stihl MS170 has a summer/winter shutter. Ensure correct positioning for your climate—open for summer, closed for winter—to route warm air to the carburetor during cold starts.
Winter Storage Preparation
If storing the chainsaw over winter:
- Run engine dry or add fuel stabilizer.
- Remove spark plug, add a few drops of oil to the cylinder, and pull starter to coat internals.
- Store in a dry, temperature-controlled environment.
Frequently Asked Questions (FAQ) About Stihl MS170 Starting Problems
Why Does My Stihl MS170 Chainsaw Flood So Easily?
The MS170’s primer and choke can quickly flood the engine if overused. Use minimal choke when engine is not cold and avoid repeated pulls with full choke. Clear flooding by removing the spark plug and pulling starter several times.
What Is The Best Fuel Mix For MS170?
Always use a 50:1 gasoline to 2-stroke oil ratio, premium-grade gas (at least 89 octane), and high-quality oil. Store the mix for no more than 30 days to prevent gums and varnish buildup.
How Often Should I Replace My Spark Plug?
Spark plugs should be checked every 25 hours of operation and replaced at least once per season or sooner if fouled. Use the manufacturer-recommended NGK BPMR7A or equivalent plug.
My MS170 Starts, Then Quickly Dies—What’s Wrong?
This often points to fuel starvation (clogged filter, carb issue), improper idle settings, or air leaks. Review the fuel system, clean the carburetor, and adjust the idle screw as needed.
When To Seek Professional Repair
If your troubleshooting steps don’t solve the problem, or you suspect issues like ignition coil failure, severe carburetor blockage, or internal engine damage, take the saw to an authorized Stihl dealer for service. Attempting major repairs without proper tools and experience can lead to further harm or void the warranty.
Genuine Stihl Parts And Warranty Advisory
Always use genuine Stihl replacement parts—plugs, filters, fuel lines—to maintain performance and uphold your warranty. Non-OEM parts may not be compatible or safe. Refer to your Stihl MS170 manual for parts numbers and approved maintenance instructions.
Safety Precautions When Troubleshooting Your Chainsaw
- Disconnect the spark plug when inspecting internal engine parts to prevent accidental startup.
- Work in a well-ventilated area when using fuel or carb cleaner.
- Wear gloves and eye protection for added safety.
- Never run the chainsaw without proper bar and chain oil to avoid engine damage.
Overview Table: Fast Solutions For Stihl MS170 Not Starting
| Issue | Indicator | Fix |
|---|---|---|
| No Spark | No ignition, repeated pulling | Clean or replace spark plug, test coil |
| No Fuel Flow | Dry plug, won’t fire | Check/replace fuel filter, refill with fresh gas |
| Flooded Engine | Strong odor, wet plug | Dry plug, clear cylinder, restart |
| Blocked Air Intake | Rough starting, stalls on throttle | Clean/replace air filter |
| Improper Starting Choke Use | Over-choked, flooding | Follow manufacturer starting sequence |
Resources For Further Assistance
- Stihl Official MS170 Product Page
- Stihl Chainsaw Manuals And How-To Guides
- Video Tutorials For MS170 Troubleshooting
These authoritative resources offer step-by-step visual guides and technical support.
Key Takeaways For Quick Fixes
- Check fuel quality and mixture first.
- Inspect spark plug and air filter next.
- Address flooding by proper choke use.
- If in doubt, consult your manual or an authorized Stihl service center.
Following these practical steps ensures your Stihl MS170 chainsaw runs smoothly and is always ready for work.