Chainsaw Starts Then Stalls, or Won't Restart When Hot: What to Check, and in Which Order
A petrol chainsaw that fires and then cuts out after 5-30 seconds is usually a fuel supply problem: check the fuel filter, then the air filter, then the tank breather, which together solve around 80% of cases according to L'Atelier. A saw that starts first thing but will not restart after a tea break is, more often than not, being started with the choke closed while warm. This guide takes both faults in the order a small-engine mechanic would.
First, name the fault precisely
A 2-stroke engine needs a spark, fuel and compression. "It won't go" can mean a fault in any of the three, so describe what actually happens before you reach for the screwdriver set.
- Starts, then cuts out after 5-30 seconds: go to the start-then-stall section; fuel supply heads the list.
- Starts cold every morning, refuses once warm: start with your technique, then flooding, the spark plug and the mix.
- Runs flat out but dies as soon as you release the throttle: think idle circuit and air filter.
- Refuses warm despite all the above: suspect an air leak or worn compression, which is a workshop job.
Starts then stalls: the five causes, by frequency
L'Atelier ranks the causes of a saw that starts instantly and then stops as follows. The percentages are the publisher's own estimate of how often each one turns out to be the culprit.
Why a chainsaw cuts out after starting
| Cause | Share | What to do |
|---|---|---|
| Clogged fuel filter | 40% | Replace the filter |
| Carburettor needle setting or dirty carburettor | 30% | Adjust the L screw, or rebuild |
| Saturated air filter | 15% | Clean or replace |
| Blocked tank breather | 10% | Clean |
| Ignition coil overheating | 5% | Measure cold and hot, replace if faulty |
The order to test them
The recommended sequence is fuel filter, air filter, breather, carburettor, coil. The carburettor is the second most common cause but comes fourth in the order: the first three checks are quick, and the source reports that 80% of cases are sorted before you get there.
- Fuel filter (in the tank). Both L'Atelier owner's guides, for the Stihl MS 261 and the Husqvarna 572 XP, say to check it when recommissioning the saw; the 572 XP guide adds the inlet hose.
- Air filter. A clogged filter shows as poor running, lack of power, stalling at idle or heavy smoke. Tap it, then blow compressed air from the inside outwards. Do not wash a felt filter; foam filters go in warm soapy water, are rinsed, dried fully and re-oiled.
- Tank breather. Ten per cent of cases, and a cleaning job rather than a part.
- Carburettor. Three screws on most saws: L (idle and low-speed mixture), H (full-throttle mixture, the critical one, as too lean means overheating and seizure) and T, LA or I (idle speed). On recent EPA or EU Stage V compliant saws the H and L screws are often limited or factory-locked: do not force them; use the manufacturer's tool.
- Ignition coil. Only 5% of cases. Measure it cold and hot before spending on a new one.
Baseline carburettor setting
Where the screws are free, L'Atelier gives this starting point: H and L screwed in, then opened one turn, then fine-tuned by ear for a steady full-throttle speed without "four-stroking" (too rich) or screaming (too lean). On saws with M-Tronic, such as some MS 261 versions, adjustment is automatic.
Won't restart when hot: technique before mechanics
"It starts perfectly in the morning, but impossible to restart after a break." L'Atelier's hot-start guide works from the free fixes to the serious ones.
- Choke open when warm. Closing the choke on a warm engine floods it immediately. Warm restart: choke open, a little throttle, one or two pulls. The source says many "hot faults" are just this.
- Clear a flooded engine. Wet plug and a smell of petrol after several pulls with the choke shut? Choke open, full throttle, pull several times to purge. On some models, remove the plug and let it dry.
- Spark plug. A fouled plug or wrong gap can work cold and fail hot. Black and wet means the mixture is too rich or there is too much 2-stroke oil.
- Fresh mix. Old fuel or a badly measured ratio upsets hot starting in particular. Make a fresh mix before going further.
- Air leak or compression. On an older saw, hardened crankshaft seals let air in once hot, the mixture runs lean and restarting becomes impossible; a worn piston ring does the same. That calls for a pressure/vacuum test.
L'Atelier's model guides make the same point from the other side: on both the MS 261 and the 572 XP, hard starting when warm points first to a saturated air filter or a tired spark plug, before any carburettor fault.
The tea-break rule
Cold start (as L'Atelier's leaf blower guide describes it for the same engine family): choke closed, a few primer presses, pull, and open the choke as soon as it catches. Warm restart: leave the choke open. If you have already flooded it, full throttle with the choke open and keep pulling.
Plug gap, mix and fuel: where the sources disagree
Three values come up during this diagnosis, and L'Atelier's pages do not always agree. We set out each figure rather than pick one; your owner's manual decides.
Values to check against your manual
| Point | What the sources say |
|---|---|
| Spark plug gap | Complete guide: typically 0.5 mm, including MS 261 (NGK CMR6H) and 572 XP (NGK CMR7H). Season-by-season guide: 0.5 mm for most Stihl, 0.65 mm for Husqvarna. |
| Mix ratio | 50:1 for nearly all modern saws (Stihl, Husqvarna, Echo): 20 ml of oil per litre of petrol, 100 ml per 5 litres. The MS 261 runs at 1:50 in every version. |
| How long a mix keeps | 30 days maximum (complete guide, MS 261 mix page). Mixing guide: degrading from 30 to 60 days, discard beyond 60. Season guide: 6-8 weeks. |
| E10 petrol | Acceptable if used within 30 days (fuel page); avoid, or use within 15 days (mixing guide); do not use unless the maker allows it (complete guide). E85: never. |
Plug torque, according to the complete guide, is typically 10-15 Nm; over-tightening damages the aluminium thread in the cylinder, under-tightening causes compression leaks. For the oil itself, the MS 261 mix page asks for JASO FD or ISO-L-EGD certified 2-stroke oil.
Mistakes that turn a ten-minute fix into a rebuild
- Adjusting the carburettor on stale fuel or with a dirty filter: you are tuning against a false baseline.
- Forcing limited H/L screws on a recent saw instead of using the maker's tool.
- Mixing straight into the saw's tank. The mixing guide says to use a clean graduated container, oil first, then half the petrol, shake, the rest of the petrol, shake again.
- Using 4-stroke engine oil (10W-40, 15W-40), used oil or cooking oil in the mix: they do not blend with petrol and will wreck the engine.
- Leaving mix in the tank over winter. Ethanol attacks carburettor membranes and fuel lines.
Keeping it starting next season
L'Atelier's maintenance table sets the rhythm: air filter cleaned every 5-10 tanks and replaced every 6 months or 100 hours, spark plug replaced yearly or every 100 hours, carburettor cleaned or adjusted once a year at the start of the season. If the saw will stand for more than 30 days, empty the tank and run the engine until it stops; restart the season on fresh mix only, and idle for 2-3 minutes before cutting.
To check a value for your own saw, you can query the L'Atelier power tools and garden machinery base: ask, for example, "What oil mix ratio does the Stihl MS 261 use, and how much oil per litre of petrol?" and the answer cites the page it comes from.
Check your saw's values at the source
Mix ratios, plug gaps, filter intervals and diagnostic order from L'Atelier's workshop guides, each answer quoting its source.
Sources on la-telier.com: top 5 causes of a chainsaw that starts then stalls, hot-start diagnosis, chainsaw maintenance guide. General information only; your manual and your dealer remain the reference.
Frequently asked questions
Why does my chainsaw cut out a few seconds after starting?
Most often a clogged fuel filter (about 40% of cases in L'Atelier's ranking), then the carburettor (30%), air filter (15%), tank breather (10%) and ignition coil (5%). Check filter, air filter and breather first.
Why won't my chainsaw restart when it's warm?
Start with technique: a warm engine is restarted with the choke open. If it is flooded, purge it at full throttle with the choke open. Then check the plug and make a fresh mix; if all fail, suspect an air leak at the crankshaft seal or low compression.
How much 2-stroke oil per litre of petrol for a chainsaw?
At 50:1, the standard for most modern Stihl, Husqvarna and Echo saws, 20 ml per litre, or 100 ml per 5 litres. Always check the ratio marked on your machine or in its manual.
Can I run my chainsaw on E10?
L'Atelier's pages differ: one accepts E10 if the mix is used within 30 days, another says avoid it and use it within 15 days if you must, and the complete guide says not to use it unless the manufacturer allows it. Follow your manual.
Is a stalling chainsaw always a carburettor problem?
No. The carburettor accounts for about 30% of cases; the fuel filter alone accounts for 40%. That is why the carburettor comes fourth in the test order.
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