Quick answer
Gas saw: it's fuel, flood, spark, or air — in roughly that order of likelihood, and stale mix is the usual root cause behind all of it. Battery saw: it's almost never the motor — check the chain brake first (an engaged brake blocks the motor completely), then the battery seating, then the trigger interlock sequence. The full order for each is below.
Gas saws: run the order
1. Fuel first
Two-stroke mix that's been in the tank more than a month or two is the prime suspect, and mix that wintered in the saw is guilty until proven otherwise. Old ethanol-blend fuel leaves sticky residue that clogs the carburetor's passages as the lighter components evaporate. Dump it, refill with fresh mix at your saw's ratio (or canned premix), and pump the primer bulb if fitted. While the cap is off, check the little in-tank pickup filter — sawdust and fuel gunk plug it, and a starving carb acts exactly like a dead one. Inspect the fuel lines for cracks; a split line sucks air instead of fuel.
2. Flooded? Clear it before anything else
If you've pulled a dozen times with the choke on and now smell raw gas, the cylinder is flooded and no amount of pulling on choke will fix it. Open the choke fully, hold the throttle wide open, and pull five to ten times — most saws cough back to life. Stubborn case: pull the spark plug, crank a few times with the plug hole open to purge fuel, let it air out, and refit a dry plug. Our Stihl-specific guide covers the Master Control Lever sequence that causes most flooding in the first place.
3. Spark plug and ignition
Pull the plug. A cracked insulator, burned-away electrode, or heavy carbon crust means replace it — don't ceremony over cleaning a worn plug. Check for spark by grounding the plug against the cylinder with the boot attached and watching for a blue snap while cranking. No spark with a known-good plug points to the ignition coil, or on many saws simply a kill switch stuck in the off position or a chewed kill-switch wire grounding out.
4. Air side: filter and spark arrestor
A sawdust-caked air filter riches the mixture until the saw can't fire; tap it out or wash it if the manual allows. And don't skip the spark arrestor — the small screen in the muffler carbons up on saws that spend life at idle, and a blocked screen will let a saw pop but never run. Pull it and clean or replace.
5. Still nothing: compression and the carb
A starter cord with no resistance means lost compression — piston or rings, and a repair-versus-replace decision on a homeowner saw. Cord feels normal but the saw only fires on fuel dribbled into the plug hole? That's the carburetor confirmed: spray-clean it first, then a rebuild kit or replacement carb if the varnish is beyond spray.
Battery saws: interlocks, not engines
A battery chainsaw showing a charged pack that does nothing when you pull the trigger is nearly always one of these, in order:
- Chain brake engaged. The front hand guard pushed forward cuts the motor circuit entirely, and a brake that's only mostly disengaged can still block it. Pull it firmly all the way back toward the handle, cycle it forward and back once, and try again. This is the number-one battery-saw "failure."
- Battery not clicked home. Pull the pack, check the contacts for debris, and reseat until it audibly clicks. Thirty seconds out of the tool also resets some packs' protection state.
- Trigger sequence. Most saws need the lockout button held before the trigger — done in the wrong order, nothing happens by design.
- Overload protection. An over-tensioned chain or a pinched bar can trip overload; back the tension off a touch and clear any debris at the sprocket.
- Pack verification. Run the battery in another tool on the same platform. Tool runs: saw's switch or interlock is the problem. Tool dead: battery or charger — and remember packs won't charge below roughly 32°F by design.
If all five pass and the saw is still silent, the trigger switch or an internal interlock has failed — warranty territory on anything young. Chain turning but won't cut, or motor runs and the chain doesn't? Different problem: see the chain won't spin guide.
Keep it from happening again
Gas saws die in storage, not in use. Either run the carb dry before a long layoff or store it on stabilized or canned fuel; drain-and-fresh every spring beats a carburetor job every second one. Battery saws just want the pack stored indoors, partially charged, and away from freezing.