Stihl MS 291 Chainsaw Tune-Up (Maintenance)
A reliable MS 291 tune-up starts with the correct fuel, bar oil, chain, and safety checks. Mix fresh gasoline and suitable two-stroke oil at 50:1. Confirm the bar’s pitch and gauge, then match the chain’s drive-link count and filing instructions. Clean and inspect the saw, sharpen or replace a dull chain, and check idle behavior before cutting.
Do you maintain your saw between weekend jobs, or are you in the shed with a dull chain and a full day’s cutting ahead? Either way, the quickest tune-up is the one that begins with the right specifications. A wrong file or chain may waste time; poor fuel or a failed safety check can cause serious trouble.
I treat “tune-up” as routine service, not a reason to adjust the carburetor by guesswork. Start with the manual and markings on your saw, bar, and chain. Parts can vary by setup, so use those identifiers rather than assuming every MS 291 has the same chain.
Equipment Setup and Safety Preparation
A pre-start check catches common problems before they reach the wood. Work on a stable surface with the engine stopped and cool. Use the operator’s manual for model-specific steps, and do not use the saw if a safety feature fails or a key part is damaged.
Confirm the bar, chain, and fuel
The bar-and-chain setup is a matched system: pitch, gauge, drive-link count, and sprocket must agree. Bar length alone does not identify the chain. Check the bar stamp and chain markings, then confirm compatibility in the manual or with a STIHL dealer.
| Item | What to check | Practical direction |
|---|---|---|
| Bar length | Bar stamp and saw manual | MS 291 setups commonly use 16–20-inch bars; confirm yours is approved |
| Chain pitch | Bar, chain, and sprocket markings | Do not assume one pitch; common MS 291 setups may differ |
| Chain gauge | Bar stamp, often shown in inches or millimeters | Examples include .050 in (1.3 mm) and .063 in (1.6 mm); match exactly |
| Drive links | Chain count or approved parts listing | Match the specified count; do not estimate from bar length |
| Fuel | Fuel container and mix | Use fresh fuel at 50:1 with suitable air-cooled two-stroke oil |
| Bar oil | Oil tank | Use chain-and-bar lubricant; do not substitute fuel mix |
STIHL specifies a 50:1 gasoline-to-two-stroke-oil ratio for this saw. That means 50 parts gasoline to one part oil, using suitable high-quality oil for air-cooled two-stroke engines. Follow the manual for approved gasoline, mix only what you can use while fresh, and label the container. Never use straight gasoline or an incorrect mix.
Inspect controls and the cutting system
PPE means personal protective equipment. Wear a helmet, eye and face protection, hearing protection, chainsaw-protective legwear, gloves, and boots. Before starting, check the chain brake, throttle trigger lockout, stop switch, chain catcher, handles, and fasteners. If a control is damaged or does not work as intended, stop and repair the saw before use.
With the engine off, inspect the chain for damage, sharpness, and correct direction. Check that the bar rails are even and not badly burred, and look at the sprocket for wear. Make sure the chain oil passages and bar groove are clear. Fill the oil tank with bar oil whenever you fill the fuel tank, then check lubrication according to the manual.
Set chain tension with the engine stopped and cool. Follow the manual’s method: the chain should sit in the bar groove and still move by hand with a gloved hand, without hanging loose underneath. A chain can loosen as it heats, so check it again during work and after the saw cools.
Next step: If the chain, bar, or sprocket markings do not match, do not fit a chain by trial and error. Confirm the approved combination first.
Field Cutting and Landscaping Operation
Safe cutting depends on a working saw and a clear plan. Before starting, inspect the work area for overhead hazards, lean, unstable limbs, escape routes, and bystanders. Keep other people well away; OSHA logging rules generally require other workers to remain at least two tree lengths away during felling.
Start the saw on firm ground, using the cold- or warm-start method in the manual. Engage the chain brake for starting and hold the saw securely. Once it is running, check that the chain stays still at idle. If it moves, stop using the saw and have the idle setting checked; do not raise the idle to compensate.
Release the brake only when you are ready to cut. Use both hands, keep stable footing, and avoid cutting above shoulder height. Keep the bar nose clear of wood and other objects. The upper quadrant of the bar nose can cause kickback if it contacts an object, rotating the saw rapidly toward you. A firm grip and working chain brake help, but they do not make tip contact safe.
For felling, use an assessed directional-felling plan and a clear escape path. Do not rely on a generic hinge measurement: tree size, species, lean, and defects affect the plan. If the tree or site is beyond your skill or equipment, stop and get qualified help.
A saw that burns wood instead of cutting cleanly, pushes fine dust, or needs force through the cut may have a dull chain. Stop, engage the brake, shut off the engine, and let the saw cool before sharpening or changing the chain. Do not force it through the wood; that adds strain and can make control harder.
Next step: If the chain moves at idle, the brake fails, or the saw behaves unpredictably, stop work and correct the fault before cutting.
Maintenance, Sharpening, and Tuning
Routine maintenance means cleaning, inspecting, sharpening, and checking operation. It does not mean turning carburetor screws until the engine sounds right. Engine speed and mixture settings need the correct service data and tools; a dealer can check them with a tachometer.
Clean the filter and check the spark plug
Remove dirt around the air-filter cover before opening it so debris does not fall into the intake. Inspect and clean the filter as the manual directs; replace it if damaged. A clogged filter can affect running, while a damaged one may let dirt reach the engine.
Inspect the spark plug for damage and deposits, following the manual’s service instructions. If the installed plug permits gap adjustment, the reference gap is 0.5 mm; verify the plug type and specification before changing it. Do not force the electrodes, and replace a worn or damaged plug with the specified type.
Sharpen using the chain’s own specifications
A file fits the cutter, not the saw model. The correct file diameter and filing angle depend on the chain marking or part number. MS 291 setups can use different chain types, so there is no safe single file size to assume from the powerhead alone.
| Chain identification | File selection | Filing angle and depth gauges |
|---|---|---|
| Marking or part number confirmed | Use that chain’s manufacturer chart or manual | Follow the specified top-plate angle and depth-gauge setting |
| Marking unclear or absent | Pause and identify the chain before filing | Do not guess by bar length |
| Applicable standard 3/8-inch chain | Check the chain maker’s instructions; some use about 5.2 mm round file | A reference depth-gauge setting may be about 0.65 mm (0.025 in); confirm chain instructions |
Use a round file held at the specified angle and height, and make consistent strokes on each cutter. Keep the same number of strokes where practical, and check that cutters remain even. Use a depth-gauge tool made for the chain type; filing the gauges too low can make the chain cut more aggressively. The chain manufacturer’s instructions take priority over general reference values.
After filing, reinstall and tension the chain as directed. Check the chain direction before starting. A chain installed backward will not cut properly.
Know when tuning needs a technician
Reference values for this model include about 2,800 rpm at idle and a maximum permissible speed near 13,000 rpm. These are not targets to set by ear. Carburetor adjustment requires model-specific service data and a tachometer; have a STIHL dealer check the settings if the saw will not idle correctly, runs poorly, or exceeds the specified limit.
| Symptom | First checks | Next action |
|---|---|---|
| Chain cuts slowly or makes fine dust | Sharpness, chain type, tension | Sharpen to chain instructions or replace a damaged chain |
| Chain moves at idle | Idle behavior and control condition | Stop use; arrange service |
| Poor cutting with a sharp chain | Chain fit, bar condition, oil flow | Check markings, groove, and oil passages |
| Engine runs poorly after fuel refill | Mix ratio, fuel freshness, air filter | Correct fuel and inspect filter; seek service if it continues |
Next step: Do not compensate for a dull chain with engine adjustments. Sharpen or replace the chain, then reassess cutting and lubrication.
Storage and Seasonal Care
Good storage keeps dirt and moisture from damaging the saw between jobs. Shut off the engine, engage the brake, and let the saw cool before cleaning or service. Follow the manual’s instructions for fuel storage and longer periods out of use.
After cutting, clean debris from the sprocket cover, bar groove, and oil passages. Inspect the chain, bar, catcher, and fasteners for damage. Recheck tension after cooling, and rotate the bar periodically to help promote even rail wear. Do not run the saw if the bar is damaged or oil is not reaching the chain.
For longer storage, use the manual’s fuel and storage procedure; fuel instructions can depend on the fuel used and storage period. Keep the saw in a dry, secure place, out of children’s reach, with the chain covered. Before the next job, repeat the pre-start check rather than assuming the saw is ready.
Workshop scenarios: two common tune-up decisions
These examples show how I separate a setup problem from an engine problem without guessing at parts.
- Scenario: the chain burns wood after filing. The operator has sharpened the cutters but has not checked the chain markings. I would stop and confirm pitch, gauge, and drive-link count, then check the file diameter and filing instructions. I would inspect the bar groove and oil flow before returning to the cut.
- Scenario: the saw idles with the chain moving. I would stop using it and check the controls and manual procedure, not adjust the carburetor by ear. A dealer can inspect the idle and verify engine speed with a tachometer.
Next step: Use the saw only when the chain fits, the safety controls work, and the chain remains still at idle.
Frequently Asked Questions
These answers cover quick service decisions for an MS 291. When chain markings or manual instructions differ from a general reference, use the model-specific and chain-specific information.
What fuel mix does the MS 291 use?
Use a 50:1 gasoline-to-suitable air-cooled two-stroke oil ratio. Follow the manual’s gasoline guidance and use fresh, correctly mixed fuel.
What chain pitch does an MS 291 take?
The setup can vary. Read the bar and chain markings and confirm the sprocket compatibility; do not assume pitch from the saw model or bar length.
What chain gauge should I buy?
Match the gauge stamped on the bar. Common examples include .050 in (1.3 mm) and .063 in (1.6 mm), but the bar marking decides.
How do I find the correct drive-link count?
Check the chain marking or approved parts information for your exact bar. Bar length alone does not provide a dependable count.
What file size should I use?
Use the chain’s identification and manufacturer filing chart. Different chain types need different file diameters, so the saw model alone is not enough.
What filing angle should I use?
Follow the instructions for the chain installed. Do not apply a generic angle without confirming the chain type.
What is the depth-gauge setting?
About 0.65 mm (0.025 in) is a reference for applicable standard 3/8-inch chain. Confirm the chain manufacturer’s instructions and use the correct depth-gauge tool.
What should the idle speed be?
About 2,800 rpm is a reference value. If the chain moves at idle, stop using the saw and have it checked rather than adjusting by ear.
When should a dealer check engine speed?
If the saw will not idle properly, runs poorly after basic checks, or may exceed its limit. The approximate maximum permissible speed is 13,000 rpm; a tachometer and model-specific service data are needed.
What should I clean after cutting?
After shutdown and cooling, clear debris from the sprocket cover, bar groove, and oil passages. Inspect the bar and chain, then recheck tension.
(This article was written by one of our staff writers, David Hensley. Visit our Meet the Team page.)
