Introduction
The Stihl MS 391 chainsaw is renowned among professional arborists and homeowners alike for its robust build, powerful engine, and reliability in demanding cutting tasks. However, even the most durable tools can encounter issues over time, potentially disrupting projects or causing safety concerns. If you're experiencing problems with your Stihl MS 391, understanding common issues, their causes, and effective troubleshooting methods is crucial. This comprehensive guide aims to shed light on prevalent problems, reveal critical gaps often missed in other articles, and provide practical solutions to ensure your chainsaw operates at peak performance.
Common Problems with the Stihl MS 391
While the Stihl MS 391 is built for heavy-duty use, users sometimes report specific issues that hinder its functionality. Let’s explore these problems in detail, analyze potential causes, and learn how to mitigate them.
- Difficulties Starting the Chainsaw
- Engine Stalling or Surging
- Reduced Power or Cutting Performance
- Chain Not Lubricating Properly
- Excessive Vibration
- Fuel or Oil Leaks
- Overheating Issues
Inadequate coverage in some articles often oversimplifies these problems or lacks detailed troubleshooting steps. Our focus here is to fill those gaps with data-driven insights and precise solutions.
Difficulties Starting the Chainsaw
Many users find their MS 391 challenging to start, especially after periods of inactivity. Common causes include:
- Fuel mixture issues
- Carburetor problems
- Spark plug malfunction
- Ignition system faults
- Dirty air filter
How to Troubleshoot & Fix:
- Check and replace old or stale fuel (use fresh 50:1 fuel mix)
- Inspect and clean or replace the spark plug
- Adjust carburetor settings following manufacturer specifications
- Clean or replace the air filter
- Ensure the spark arrestor isn't clogged
Engine Stalling or Surging
Engine stalling can be frustrating and dangerous, often indicating choke or carburetor problems.
Possible Causes:
- Improper carburetor adjustment
- Clogged fuel lines
- Vacuum leaks
- Faulty fuel filter
Troubleshooting Steps:
- Check fuel lines for obstructions or leaks
- Clean the carburetor’s air passages
- Adjust the carburetor idle speed screw
- Replace the fuel filter if clogged
Reduced Power or Cutting Performance
A chainsaw that underperforms can stem from chain issues, fuel problems, or engine health.
Common Causes:
- Dull chain
- Insufficient chain oiling
- Dirty or clogged muffler
- Worn spark plug
- Air or fuel filter clogging
Solutions:
- Sharpen or replace dull chain
- Ensure chain oil reservoir is filled and the oil line isn't kinked
- Clean the muffler to remove carbon buildup
- Replace spark plug if electrodes are worn
- Replace or clean filters regularly
Chain Not Lubricating Properly
Inadequate lubrication leads to increased wear and safety risks.
Common Reasons:
- Blocked oil port
- Dirty or worn chain sprocket
- Low chain oil levels
Remedial Actions:
- Check and clean oil ports
- Replace worn sprockets
- Keep the oil reservoir topped up with proper bar and chain oil
Excessive Vibration
Vibration can cause fatigue and reduce operational precision.
Causes & Fixes:
- Loose chain or bar nuts
- Worn engine mounts
- Damaged or bent chain
Tighten nuts and replace damaged components; regularly inspect chain tension.
Fuel or Oil Leaks
Leaks can pose safety hazards and indicate seals or fittings failure.
Troubleshooting:
- Inspect fuel cap gaskets and replace if cracked
- Tighten fittings
- Replace worn or damaged seals
Overheating Issues
Overheating can reduce engine life and performance.
Contributing factors:
- Dirty cooling fins
- Excessive engine load
- Low oil in the chain oil reservoir
How to prevent:
- Regularly clean cooling fins
- Avoid overworking the chainsaw
- Maintain adequate chain oil levels
Materials Needed for Troubleshooting and Repairs
| Item | Purpose | Specifications |
|---|---|---|
| Replacement Spark Plug | To replace faulty ignition component | NGK BPMR7A or equivalent |
| Chain File and Sharpening Kit | Sharpen dull chain | Suitable for the chain pitch |
| Carburetor Cleaner | Clean carburetor components | High-quality, STIHL-approved cleaner |
| Bar & Chain Oil | For lubrication during operation | Proper viscosity for chainsaws |
| Replacement Fuel and Oil | To refill fuel mixture and chain oil reservoir | Premium, fresh mix |
| Gasket & Seal Kit | Replace worn seals and gaskets | OEM parts preferred |
| Tools (Screwdrivers, Wrenches) | General disassembly and adjustments | Set including Phillips, flat-head |
Tips for Troubleshooting Success
- Always use fresh fuel—stale fuel causes starting and performance issues.
- Perform regular maintenance, including cleaning air filters, replacing spark plugs, and checking chain tension.
- Follow the manufacturer's recommended carburetor tuning procedures meticulously.
- Keep a record of maintenance activities to monitor performance trends.
- Test run each repair step to confirm fixes before proceeding further.
Common Mistakes and How to Avoid Them
- Ignoring regular maintenance: Regular servicing prevents many common problems.
- Using incorrect fuel or oil mixtures: Always adhere to the manufacturer's specifications.
- Over-tightening chain tension: Excessive tension increases wear and reduces efficiency.
- Neglecting safety precautions: Always wear protective gear and disconnect spark plugs during repairs.
- Delaying repairs: Small issues can escalate into costly damages if ignored.
Summary
Troubleshooting the Stihl MS 391 involves systematically diagnosing issues, understanding common causes, and applying targeted fixes. By maintaining proper care routines, using quality parts, and addressing problems promptly, you can extend the lifespan of your chainsaw while ensuring safe and efficient operation. Remember, a well-maintained chainsaw not only performs better but also enhances safety during demanding tasks.
In conclusion, comprehensive knowledge of your Stihl MS 391’s potential problems and their solutions empowers you to keep it running smoothly. Regular maintenance and proactive troubleshooting will save you time, money, and frustration, enabling your chainsaw to perform reliably for years to come.