Lauren HollandBy Lauren Holland

Updated November 2026

When a Craftsman gas lawn mower won’t start, the cause is usually one of a few simple problems: stale or missing fuel, a fouled spark plug, a clogged air filter, or a setting or safety switch that isn’t where it should be. This guide walks through the checks in the order that solves the most failures, so you can get the mower running without tearing into the engine.

Check the Fuel and Starting Position

Start with the basics. Gasoline that has sat for more than about 30 days can break down and leave varnish in the carburetor, and ethanol-blended fuel draws moisture over time. If the tank is low, the engine may not draw enough fuel to fire at all.

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  • Drain old fuel and refill with fresh unleaded gasoline rated for small engines.
  • Confirm the fuel shutoff valve (if equipped) is open.
  • Move the throttle to the fast or run position and set the choke to closed for a cold start, or open once the engine has fired.
  • Make sure the operator presence bar is held against the handle while you pull the starter cord.

Inspect the Spark Plug

A spark plug that is fouled, cracked, or has the wrong gap will prevent ignition even when fuel is present. Remove the plug with a socket wrench, check the electrode for black carbon or oil, and look at the porcelain insulator for cracks. Manufacturers typically specify a gap of roughly 0.030 inch for Craftsman-branded engines, but confirm against your owner’s manual before adjusting.

If the tip is heavily coated, clean it or replace it. Reconnect the boot firmly, since a loose wire connection can cause a no-spark condition.

Clean the Air Filter and Carburetor

A restricted air filter starves the engine of air and can flood it with fuel. Tap or wash a paper filter, and replace it if it is torn or oil-soaked. Foam filters can be washed in mild soap and water, dried, then lightly oiled.

If fuel was left sitting in the mower, varnish may have gummed up the carburetor jets. Many owners find that a spray carburetor cleaner through the intake, along with a fresh fuel fill, restores running. Avoid probing jets with wire, which can enlarge them.

When to Stop and Get Help

If the carburetor needs to be disassembled, or the flywheel brake or blade engagement is involved, consult a qualified small-engine technician. Gasoline is hazardous, so work outdoors with the spark plug wire disconnected.

Common Mistakes

  • Priming repeatedly on a hot engine, which floods it with fuel.
  • Leaving the choke closed after the engine has started.
  • Storing the mower with gas still in the tank.
  • Skipping the operator presence bar, which keeps the engine from running.
  • Replacing the spark plug without checking the air filter and fuel first.

A spark plug socket with a rubber insert holds the plug while you remove it without dropping it into the engine. View on Amazon

A carburetor cleaner spray with a straw nozzle lets you reach the intake and jets without disassembly. View on Amazon

Fuel stabilizer added to the tank before storage helps prevent varnish from forming during the off-season. View on Amazon

FAQ

Why does my Craftsman mower start, then die right away?

This usually points to a clogged air filter, a fuel delivery problem, or the choke being left on. Check the filter first, then confirm the choke is fully open once the engine fires.

How long can gas sit in a Craftsman mower before it causes problems?

Fuel more than about 30 days old can start to degrade, especially ethanol blends. Adding a stabilizer or running the engine dry before storage prevents most trouble.

Should I replace the spark plug if it looks fine?

If the plug is clean and the gap is correct, it may be fine. Replacing an inexpensive plug is still a quick test when other causes have been ruled out.

Conclusion

Work through fuel, the spark plug, and the air filter before touching anything more complicated, since these fix most no-start complaints. Keep the operator bar and choke positions in mind, and use fresh fuel to avoid repeat problems. If the mower still won’t start after these checks, a small-engine shop can diagnose the carburetor or ignition system.

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Lauren Holland

About Lauren Holland

Lauren Holland is part of our editorial team and reviews and edits our lawn mowers guides, checking product details against manufacturer specifications and owner feedback.