Chainsaw Won't Start or Won't Stay Running? The Complete Troubleshooting Guide (UK)

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Chainsaw Won't Start or Won't Stay Running? The Complete Troubleshooting Guide (UK)

By Jim Fellows, Garden Machinery Specialist · Updated 23 July 2026 · 11 min read

Chainsaws live the worst storage life in the shed: used hard for a few autumn weekends, then parked with mix in the tank for ten months. The engine problems that follow are the familiar small-engine trio — fuel, spark, air — with a two-stroke accent, plus the chainsaw-only systems (chain brake, clutch, oiler) that add their own symptoms. Here's the full map.

Battery saw refusing to power up? The battery seating, temperature and lockout rules in our cordless troubleshooting guide apply directly — then rejoin this guide at the chain and oiler fixes, which are shared.

Fast Diagnosis: Symptom → Likely Cause

Fix 1: Fresh mix, exact ritual

Two-stroke mix degrades even faster than straight petrol — treat anything older than a month as the prime suspect. Dispose of the old mix properly and make fresh with a quality two-stroke oil at exactly your manual's ratio (a mixing bottle removes the guesswork; ratio errors starve the engine of lubrication or coke the plug). Then start it the way the manual choreographs it: prime the bulb the stated number of times, full choke, pull until the first cough, half choke, pull to run, throttle blip to release. Skipping straight to full-choke pulling past the cough is how Fix 2 happens.

Fix 2: Flooded — patience beats pulling

Petrol smell and a wet plug mean the cylinder is flooded. Choke fully open, plug out, a few gentle pulls to air the cylinder (rag over the plug hole), plug dried or replaced, fifteen minutes' rest, then restart with no choke and — if your throttle allows — held open. Repeated priming and full-choke pulling only deepens the flood.

Fix 3: Starts then dies — the fuel path

Same disease as every stored petrol machine: varnish restricting the carburettor, with two chainsaw-specific extras. First, the in-tank fuel filter — a small filter on the end of the fuel line inside the tank, fishable out with a bent wire; if it's brown and crusted, replace it. Second, the air filter, which on a saw clogs with fine sawdust rather than grass dust — tap or brush it clean, replace if glazed. Fresh chainsaw filters are cheap, model-specific consumables. If it still dies, the carburettor needs cleaning — the principles in our carburettor guide apply, but on a saw the carb is smaller and fiddlier, and the tuning screws (H/L/idle) are factory-set for emissions and engine safety: clean, don't adjust. A saw that only behaves with the screws fiddled belongs at a workshop.

Fix 4: Engine runs, chain won't move

Check the obvious first: the chain brake — the front hand guard — engaged. Pull it back towards the handle until it clicks and the chain is freed; saws are routinely carried and stored with the brake on (correctly), then declared broken. Also check chain tension: an over-tightened chain binds on the bar. Correct tension lets the chain lift a few millimetres from the bar and pull round by (gloved) hand with the engine off. If the brake is off, tension is right and the chain still won't drive under throttle, the clutch is slipping or the brake band is dragging — workshop territory, and a saw that spins its chain at idle is the reverse fault and equally a stop-using-it-now workshop job.

Fix 5: Cutting dust, not chips — sharpen the chain

A sharp chain pulls itself into the wood and throws proper chips; a dull one makes powder, smoke and hard work, and invites the pressing that causes accidents. Sharpening is core chainsaw ownership: a round-file sharpening kit in the file size your chain specifies, equal strokes on every cutter at the marked angle, with the depth gauges dressed per the kit's guide. Rocks, soil contact and fencing wire kill edges instantly — and a chain that's been repeatedly sharpened, has damaged cutters, or has stretched beyond its tensioner's range gets replaced: match a replacement chain to your bar length, pitch and gauge exactly (all three are stamped on the bar).

Fix 6: Dry bar — the oiler

The chain must run wet. Check the oil tank is filled with proper bar and chain oil — its tackiness is the point; engine oil flings off and used oil is a false economy that wrecks bars. Test the oiler by running the saw (chain safe, over cardboard or a stump) and looking for the fine oil line it should throw. Nothing? With everything off, remove the bar, clean the oiler outlet port on the saw body and the oil holes and groove on the bar itself — sawdust paste blocks them constantly — and flip the bar while you're there, which evens its wear. A dry-running chain blunts in minutes and blues the bar; the oiler check is a ten-second habit at every refuel.

Frequently Asked Questions

Why won't my chainsaw start after winter?

Stale two-stroke mix, almost every time — it degrades within about a month and gums the carburettor. Fresh mix at the manual's ratio, the exact cold-start sequence, and a check of the plug, air filter and in-tank fuel filter revive most stored saws.

Why does my chainsaw start then cut out?

Fuel restriction: a varnished carburettor, a crusted in-tank fuel filter, or a sawdust-choked air filter. Replace the cheap filters first, then clean the carb — but never adjust its tuning screws; that's a workshop calibration.

Why is my chainsaw not spinning the chain?

Check the chain brake — the front hand guard clicks back towards the handle to release — and the chain tension, which binds when over-tight. Brake off and tension right but still no drive means clutch trouble; and a chain that moves at idle is a dangerous fault requiring immediate professional attention.

Why is my chainsaw smoking or cutting slowly?

A dull chain or a dry bar — often both, since a dry chain blunts fast. Sharpen with the correct file size, confirm the oiler is wetting the chain, and use proper tacky bar oil. Fine dust instead of chips is the classic dull-chain signature.

Can I use old engine oil on my chainsaw chain?

No. Chain oil is formulated tacky so it clings at speed; engine oil — especially used oil, with its suspended metal particles — flings off, leaves the chain dry, accelerates bar wear and coats you and the log in spray. Proper bar oil is one of the cheapest items in the whole hobby.

Garden Review is reader-supported. As an Amazon Associate we earn from qualifying purchases made through links on this page, at no extra cost to you. This does not influence our advice. Always follow your machine's manual and safety instructions, use appropriate protective equipment, and if in doubt — or under warranty — consult the manufacturer's official support.