Chainsaw Won't Start? What to Check

Part of our complete Small Engine Troubleshooting Guide.

Work through it in this order. The first two steps cost nothing and account for most of the saws that reach us as a no-start, and the later steps are the ones worth paying someone to do properly.

1. The Controls Come Before the Engine

More saws arrive here with nothing wrong than you would believe. The master control or ignition switch has to be on, and on saws where one lever does switch, choke and fast idle together it is easy to leave it between positions where it does nothing. If the saw has a fuel valve, it has to be open.

Set the choke closed for a cold start, pull until it coughs, then open the choke before carrying on — that cough is the saw telling you it has fuel. A larger saw with a decompression button needs it pressed before every pull, and a chain brake left off makes a saw dangerous to start rather than unwilling.

2. Last Season's Mix Fuel Is the Usual Culprit

Two-stroke mix does not keep. Ethanol-blended pump gasoline starts going off within weeks, and a can mixed last winter is a different liquid by firewood season: it carries water, it has lost the light fractions a cold engine needs to fire, and it leaves varnish behind in a carburetor whose passages are barely wider than a pin.

The oil ratio matters as much as the age. Too little oil and the engine is at risk the moment it does run; too much and the plug fouls and the saw will not fire at all. Mix at the ratio the manual gives, with oil made for air-cooled two-strokes, in small enough batches that none of it sits for long — our guide to ethanol gas and small engines covers why it goes bad so quickly.

3. Work the Fuel Path, Not the Carburetor

If fresh fuel alone does not fix it, follow the fuel from the tank forward before anyone takes a carburetor apart. Four things go wrong, and all four are cheap:

• The primer or purge bulb. It should firm up and stay firm. One that stays soft, or that cracks when you squeeze it, is drawing air instead of fuel.
• The fuel line. Years of fuel and heat leave it hard and split, usually right where it leaves the tank or passes the cylinder.
• The filter in the tank. There is a small felt or mesh filter on the end of the pickup hose, and it clogs with the sediment that stale fuel drops. It is a two-minute job with a bent wire.
• The main jet. If the fuel and filter are good and it still will not run, the varnish is inside the carburetor — see our guide to small engine carburetor cleaning.

4. Flooded, and the Routine That Makes It Worse

The commonest way to kill a start is to keep pulling with the choke closed. Each pull after the first cough pushes more fuel into a cylinder that already has enough, and eventually the plug is wet and no spark will light anything. A saw that fires once and then refuses everything is usually flooded rather than faulty.

Open the choke fully, use whatever flood-clear or fast-idle position the manual specifies, and pull steadily several times to push the excess through. If it still will not go, take the plug out, dry it, leave the cylinder open for a minute and refit it. Then start again from a cold-start sequence rather than from where you left off.

5. Spark, and the Screen Nobody Checks

Pull the plug and read it. Dry and sooty black says it has been running rich or the plug is worn out; wet with fuel says flooded; pale and dry with no smell at all says it is getting no fuel, which sends you back to step three. Check the gap against the manual, make sure the lead is pushed properly onto the terminal, and replace a plug that has done a couple of seasons rather than cleaning it.

The other half of the ignition side is the spark arrestor screen in the muffler. A saw runs rich, cuts in a dirty place and spends its life at full throttle, so that screen packs with carbon faster than on any other machine we see. A blocked one shows up as a saw that will not start hot, or that starts and then fades away to nothing under load.

6. When It Belongs on a Bench

Three faults are worth stopping for. A cord that pulls over with no resistance at all means compression has gone, and no amount of fuel or spark will change it — stop pulling and have it measured. A saw that starts, revs and then will not idle, or that will only run with the choke part closed, is usually drawing air past the crankshaft seals or the intake boot, which is a pressure test rather than a guess.

The third is the starter itself. A cord that will not retract, or a pull that spins without turning the engine, is a broken recoil spring or worn pawls rather than an engine fault — our guide to recoil starter and pull cord repair covers what is inside that housing. The same no-start logic applies to the rest of the two-stroke family, and our guide to a leaf blower that will not start works through it on a smaller machine.

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Matching the Symptom to the Cause

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When to Call the Shop

Fresh mix fuel, a new plug, a primer bulb, a tank filter and a cleaned arrestor screen are all driveway jobs, and between them they wake up most saws that have simply sat too long. If one of them fixes it, note which, because a saw stored the same way next spring will do the same thing again.

Bring it to us when fresh fuel and a clean filter change nothing, when the carburetor needs stripping rather than a squirt of cleaner, when compression or a crankcase leak needs measuring, or when the recoil has come apart. We will tell you what it needs and what it is not worth spending on, and the chainsaw maintenance it is due anyway — chain, bar, oiler and filters — can be done while it is already on the bench.

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Chainsaw No-Start FAQ

Why won't my chainsaw start after sitting all summer?
Usually last season's mix fuel. Two-stroke blends go stale in weeks and leave varnish in passages the size of a pin hole. Drain it, refill with fresh mix, and check the primer bulb and the tank filter before anything else.

How do you start a flooded chainsaw?
Open the choke fully, follow whatever flood-clear position the manual gives, and pull steadily several times to push the excess through. If the plug is soaked, take it out, dry it off and let the cylinder air before refitting it.

What fuel mix does a chainsaw need?
Whatever ratio the manufacturer specifies in the manual, with two-stroke oil made for air-cooled engines. Mix it fresh in small amounts rather than keeping a can going all season, and shake the can before filling.

Do you repair chainsaws in Richmond, KY?
We do, across Madison County. Carburetor cleaning and rebuilds, fuel lines and filters, ignition parts, recoil starters, compression testing and chain sharpening, with pickup and delivery available and a firm quote before any work begins: (859) 661-8877.