Why won't my chainsaw start?

The quick answer

A gas chainsaw that will not start is almost always short of one of three things: fuel, air or spark. Work through them in that order, because the cheapest causes come first. University of Missouri Extension's troubleshooting table for an engine that will not start lists the switch off, an improper starting procedure, an empty fuel tank, a flooded engine, incorrect carburetor adjustment and a fouled spark plug.^[1]

Before you pull the cord

Starting a saw to test it is still running a saw. Extension guidance is that PPE should be worn even when simply starting a saw to ensure it is running properly.^[2] That means hearing protection, goggles, leather gloves and chain saw chaps.^[2]

Set the saw on level ground clear of rocks, with the bar and chain up out of the dirt. Put one foot in the rear hand guard, grip the top handle firmly with one hand and pull the starting rope with the other.^[1] Never drop-start the saw: you can hold it with only one hand and you have no control over the swinging action of the bar.^[1]

Check the simple things first

Is the stop switch on? Is there fuel in the tank? Both are on the Extension list, and both are missed more often than anyone admits.^[1] Then check that you are following your saw's own starting sequence. Saws differ in how they use the choke, primer bulb and decompression valve, so the owner's manual beats any general advice here, and a wrong sequence can flood the engine.

Suspect the fuel

If the saw has sat for a season, the fuel is the likeliest culprit. Gas begins to degrade in as little as 30 days, which can clog the fuel system and keep equipment from starting.^[4] Penn State Extension says engines that are rarely or seasonally used, such as lawnmowers or chainsaws, are especially prone to difficulties with ethanol-blended fuel.^[3]

Pour the old fuel into an approved container and refill with fresh gasoline mixed with two-cycle oil as the manufacturer recommends.^[1] Do not use waste crankcase oil in the mix, and carry the fuel in a UL-listed or Factory Mutual approved safety can.^[1] If the saw runs and then dies, check the vent in the fuel tank cap: the Extension table lists a plugged vent as a cause of an engine that dies or accelerates poorly.^[1]

Air and spark

The same table lists a dirty air cleaner as a cause of an engine that dies or accelerates poorly, so clean it.^[1] Tap out the dust, wash a foam element in warm soapy water if the manual allows, dry it, and refit it.

A fouled or wet spark plug is the other classic. For a flooded engine the table's correction is to clean the spark plug, and for a fouled plug it is to clean or replace it.^[1] With the saw off and cool, pull the plug boot, unscrew the plug with the wrench from the tool pouch, look at it, and let a wet plug dry before refitting. A plug that is black, oily or cracked should simply be replaced with the type in your manual.

What not to touch

Carburetor adjustment is on the list, but it is the one item to leave to a shop unless you know the saw. Set wrongly, the idle screw can make the chain creep when the engine idles. Extension's maintenance table says the chain must not rotate at idle.^[2] Likewise, the chain brake is a safety device; Extension says maintenance on it is critical and repairs should be done by properly trained service technicians.^[1]

Stop and call a pro if

• The saw still will not start after fresh fuel, a clean air filter and a clean or new plug. The cause is probably a carburetor, ignition or compression fault.
• The pull cord is stiff, will not pull or snaps back. The engine may be seized or the recoil starter broken. Do not force it.
• The chain moves at idle, or the chain brake does not stop it. Stop using the saw.
• You smell fuel around the saw, or see fuel leaking from the tank, lines or carburetor. Keep ignition sources away and have it repaired.
• Repair costs are creeping toward the price of a new saw. Read whether an old chainsaw is worth repairing before you pay for parts.

Getting help in Virginia

For typical shop prices, see what chainsaw repair costs in Virginia. If the saw does start but cuts badly, check the chain tension first. See chainsaw repair or more small engine repair answers.

When you are ready, post a chainsaw repair job and local shops can quote it.