Stihl MS 291 No-Start Diagnostics (Troubleshooting)
If your STIHL MS 291 will not start, stop pulling and check it in order: safe setup and starting procedure, fuel and flooding, air and exhaust, spark, then compression. Use fresh 50:1 premix, follow the saw’s manual for cold or warm starts, and avoid carburetor adjustments by guesswork. A simple check can prevent unnecessary parts replacement.
A stalled saw can derail a weekend job, and replacing parts without a test can cost more than the repair. Start with the checks you can do safely beside the workbench, then move to tests that need the right tools or a service technician.
The MS 291 is a 55.5 cm³, two-stroke chainsaw. It needs the correct fuel mix, air, spark, and compression to run. Check one system at a time and note what you find. That keeps a wet plug, for example, from being mistaken for a bad ignition coil.
Equipment Setup, PPE & No-Start Safety Checks
A no-start check begins with a safe saw, not another pull. Wear eye and face, hearing, hand, leg, and foot protection. Work outdoors on firm ground, keep people clear, and secure the saw as the manual directs. Inspect the controls, chain brake, bar, and chain before starting.
Set the stop switch to RUN and engage the chain brake for starting. Check that the chain is correctly tensioned and has no damage. Use only a bar-and-chain combination approved for your exact saw version. Pitch, gauge, and drive-link count must fit the bar and sprocket; do not assume every MS 291 has the same gauge or chain length.
The chain is commonly supplied in 3/8-inch pitch, but the bar stamp is the authority for its gauge and drive-link count. If the bar or chain is mismatched, damaged, or loose, do not start the saw until the issue is corrected.
Look for fuel leaks, loose parts, or damage. If you see a leak or cannot operate a control normally, stop and repair the problem before starting. The chain brake is not a substitute for holding the saw correctly or keeping the chain clear of people and objects.
Next step: Once the saw and work area pass inspection, verify the start procedure and fuel before inspecting parts.
Field Starting and Cutting Operation
Starting procedure means using the choke and control settings for the saw’s temperature and following the sequence in its current manual. A cold engine needs the prescribed cold-start sequence; a warm engine should not be given full choke. If it fires, move to the manual’s run position promptly.
Check the fuel before pulling again. The MS 291 uses gasoline premixed with STIHL two-stroke oil at 50:1, or another oil explicitly rated for air-cooled two-stroke engines at that ratio. Do not use straight gasoline, an unknown mix, or fuel that may be stale. Empty questionable fuel using safe handling practices and refill with fresh, correctly mixed fuel.
Confirm there is adequate bar-and-chain oil, too. This oil is separate from the engine fuel. Use STIHL bar-and-chain oil or an equivalent tacky chain lubricant. Do not use a guessed flow-rate target; verify oil delivery by the procedure in the manual.
| What you notice | Likely direction | Safe next check |
|---|---|---|
| Saw has not fired after repeated full-choke pulls | Flooded engine possible | Stop using full choke; follow the manual’s clear-flood procedure |
| Plug is wet after removal | Fuel is reaching the cylinder, but may be excessive or not burning | Dry or replace only as the manual permits; check spark and starting procedure |
| Plug is dry after correct starting attempts | Fuel may not be reaching the cylinder | Check fuel age, tank vent, filter, and lines |
| Saw fires, then dies | Starting sequence, fuel supply, or air/exhaust restriction | Follow the run-position procedure; inspect filter and muffler |
| Chain moves at idle | Unsafe idle or clutch-related fault | Stop the saw and get it repaired before use |
Repeated pulls with full choke can flood the engine and foul the spark plug. Do not keep pulling in that setting. Use the model’s prescribed clear-flood steps rather than improvising. If the engine starts, let it stabilize at idle. The chain must not move at idle; if it does, stop the saw and do not cut.
Next step: If the correct start procedure and fresh fuel do not work, move through the least invasive checks below.
No-Start Diagnosis: Fuel, Air, Spark, and Compression
Diagnosis means testing likely causes in a set order, from simple checks to deeper engine tests. This limits unnecessary part changes. For an MS 291 that will not start, check fuel and flooding first, then air and exhaust, then spark, fuel delivery, and compression.
Start with the air filter. Remove and inspect it as directed in the manual. Clean or replace it using the approved method; do not run the saw without the filter. A clogged filter can restrict air, while a filter soaked with fuel or oil may need service before it can work correctly.
Next inspect the spark plug for fouling, damage, or wetness. A wet plug can point to flooding, but it does not prove the ignition system works. A dry plug after correct starting attempts may point toward a fuel supply problem, but it does not prove the carburetor is faulty. Refit the correct plug as specified for the saw.
Test spark with an appropriate inline or adjustable spark tester, following its instructions and the saw’s manual. Keep fuel away from the test area and do not hold a plug by hand while cranking. No visible spark with a proper tester calls for checks of the stop-switch circuit, wiring, and ignition components; those tests may require a technician.
If spark is present but the plug remains dry, check the fuel filter and fuel lines for blockage, damage, or leaks. A restricted tank vent can also interrupt fuel flow. Inspection does not confirm a carburetor fault. Do not adjust carburetor screws by guesswork; incorrect settings can harm the engine or create unsafe operation.
Check the muffler and spark-arresting screen, if fitted, for blockage, using the manual’s removal and cleaning instructions. Work only on a cool saw. A blocked exhaust can prevent normal running, but cleaning it will not fix a separate spark or fuel fault.
If fuel, air, exhaust, and spark checks do not explain the failure, compression needs testing with a suitable gauge and the correct procedure. Compression is the pressure made as the piston moves in the cylinder. There is no single field number here that fits every test method and saw condition, so compare results with STIHL service data for the exact version. Low readings or signs of cylinder damage need professional diagnosis.
| Check | Result | What it suggests | Next action |
|---|---|---|---|
| Fresh 50:1 fuel, correct start steps | Still no start | Continue; fuel quality alone is not the answer | Inspect filter, plug, and air filter |
| Spark tester shows no spark | Ignition or stop circuit issue possible | Do not replace the coil without further tests | Check switch and wiring; refer for service if needed |
| Plug dry after proper attempts | Fuel delivery may be restricted | Filter, vent, lines, or carburetor may need inspection | Check accessible parts per manual |
| Spark present, fuel and air checks pass | Compression or timing-related fault possible | Needs suitable equipment and service data | Arrange a compression test and repair assessment |
Next step: Record each result. If basic checks pass, stop replacing parts and move to proper service testing.
Maintenance, Chain Sharpening & Engine Tuning
Maintenance affects starting and safe operation, but it is not a reason to tune by ear. Keep the air filter, cooling-air intake, bar groove, sprocket cover, and chain maintained as the manual directs. Shut down, allow the saw to cool, and remove the spark-plug boot when the manual calls for it before cleaning or inspection.
A dull or damaged chain affects cutting, not whether the engine starts. Sharpen it to the chain manufacturer’s instructions and set depth gauges to that chain’s specification. A 0.65 mm (0.025 in) depth-gauge setting is common for some STIHL chains, but it is not universal. Check the chain’s own specification rather than applying that number to every chain.
Idle speed is approximately 2,800 rpm. If the chain moves at idle, stop using the saw immediately. The idle setting or clutch may need service. Maximum engine speed varies by model version; use current STIHL technical data and the specified tachometer procedure. Do not set it by ear or use an unverified adjustment.
A useful diagnostic pattern is to change only one thing at a time. For example, if a saw fires after the correct clear-flood procedure, that supports flooding as part of the problem; it does not prove the carburetor is healthy. If it starts but then dies, note how long it runs and whether the plug is wet or dry before deciding what to test next.
Next step: After a successful start, confirm stable idle, no chain movement at idle, and bar-oil delivery before cutting.
Storage, Fuel Management & Seasonal Care
Fuel management means keeping the saw’s premix fresh and correctly mixed, then following the manual’s storage instructions. The MS 291 requires 50:1 premix. Never add straight gasoline or use an unknown ratio; incorrect fuel can damage a two-stroke engine.
If the saw has been stored, do not assume old fuel is still usable. Check the fuel’s age and condition, and replace questionable fuel with a fresh, correct mix. Inspect the plug and filter if it still will not start. Follow the manual for longer-term storage, including how to handle fuel in the tank and carburetor.
After use, shut down the saw and let it cool before cleaning. Clear debris from the air-intake area, bar groove, and sprocket cover as instructed. Keep fuel and ignition checks separate from hot or running parts, and do not attempt repairs around an active chain.
Next step: If fresh fuel and routine service do not restore starting, use test results to guide service rather than buying parts at random.
FAQs About an MS 291 That Will Not Start
Why will my MS 291 not start after many pulls?
Repeated full-choke pulls may flood the engine. Stop pulling and follow the manual’s clear-flood procedure. Then use the correct start sequence for a warm engine.
What fuel mix does an STIHL MS 291 use?
Use fresh gasoline mixed with STIHL two-stroke oil at 50:1, or an equivalent oil rated for air-cooled two-stroke engines. Do not use straight gasoline or an unknown mix.
Should the spark plug be wet or dry?
Neither condition alone gives a complete diagnosis. A wet plug can indicate flooding; a dry plug can suggest fuel is not reaching the cylinder. Check spark and fuel delivery before replacing parts.
Can I adjust the carburetor to make the saw start?
Do not adjust it by guesswork. Fuel lines, filters, ignition, or compression may be the cause, and incorrect carburetor settings can create engine damage or unsafe operation. Use STIHL service data or a qualified technician.
How do I know if the ignition has spark?
Use a suitable spark tester according to its instructions and the manual. Keep fuel away from the test area. If there is no spark, test the stop-switch circuit and wiring before condemning the ignition coil.
What if the saw starts and then stalls?
Check that you moved to the correct run position after it fired. If it still stalls, inspect the air filter, fuel condition, tank vent, fuel filter, lines, and muffler for restriction or damage.
What chain size does an MS 291 need?
Do not choose by model name alone. Match pitch, gauge, and drive-link count to the bar stamp and sprocket, and use a combination approved for your exact saw version.
Is it safe to cut if the chain moves at idle?
No. Stop the saw and correct the fault before cutting. A moving chain at idle can cause severe injury; have the idle or clutch system checked if needed.
(This article was written by one of our staff writers, Robert Callahan. Visit our Meet the Team page.)
