Graham FisherBy Graham Fisher

Updated November 2026

If your Craftsman 150cc lawn mower won’t start, the cause is usually something simple: stale fuel, a fouled spark plug, a clogged air filter, or a choke setting that doesn’t match the engine’s temperature. This guide walks through the checks in the order that solves the most no-start problems, so you can stop guessing and get the mower cutting again.

Check the Fuel and Oil First

Most no-start complaints trace back to fuel. Gasoline that has sat for more than about 30 days can gum up the carburetor jets, and ethanol-blended fuel tends to absorb moisture over time. Drain the old fuel into an approved container, refill with fresh gasoline, and confirm the oil is at the full mark on the dipstick. Many Craftsman 150cc engines include an oil-level safety feature that prevents starting when the oil is low, so a low reading can look like a fuel or electrical fault.

Shopping for one? See our guide: Craftsman M220 Lawn Mower Won't Start: 7 Best Recoil Starter Replacements (2026).

Inspect the Spark Plug

A spark plug that is wet, sooty, or has a worn electrode can prevent ignition even when fuel is present. Remove the plug, check the gap against the value in your owner’s manual, and look at the tip. Replace the plug if the electrode is rounded or the insulator is cracked. Before reinstalling, confirm the spark plug wire or boot is fully seated.

Clean or Replace the Air Filter

A restricted air filter starves the engine of air and produces a rich condition that floods the cylinder. Remove the cover, tap out loose debris, and inspect the element. Foam filters can be washed and lightly oiled, while paper filters should be replaced when they are dirty or oil-soaked.

Set the Choke and Throttle Correctly

Starting a cold engine usually requires the choke to be closed, while a warm engine often needs it open or only partly closed. Follow these steps:

  1. Set the throttle to the fast position.
  2. Move the choke to the closed position for a cold start.
  3. Pull the recoil starter firmly several times.
  4. Once the engine fires, gradually open the choke.

If the engine is already warm, try starting with the choke open or only partly closed. A flooded engine is often cleared by setting the choke open, turning the throttle to fast, and pulling the starter with the spark plug removed for a few pulls before reinstalling the plug.

Verify the Safety Systems and Starter

Confirm the operator presence control bar is engaged or that the blade control is in the correct position, depending on your model. Check that the recoil starter rope pulls out smoothly and retracts fully. If the rope stays loose or the pulley doesn’t engage, the starter assembly may need service.

Common Mistakes

  • Priming repeatedly on a flooded engine, which only makes the problem worse.
  • Leaving old gasoline in the tank over the off-season.
  • Ignoring a fouled spark plug and replacing the carburetor first.
  • Running the mower with the air filter cover missing.
  • Spark plug socket and gap tool lets you remove and check the plug without damaging the threads. View on Amazon
  • Fuel stabilizer keeps gasoline usable during storage and reduces varnish buildup. View on Amazon
  • Approved fuel container makes it safer to drain and store old gasoline. View on Amazon

FAQ

Why does my Craftsman mower start and then die?

This usually points to a choke that is closed too long or a carburetor that needs cleaning. Open the choke once the engine runs smoothly and check the air filter for restriction.

How often should I replace the spark plug?

Many owners replace it once a season or every 50 hours of operation, but always follow the interval in your owner’s manual. A plug that looks worn or fouled should be replaced regardless of hours.

Can I use gasoline that has been sitting all winter?

It is best to avoid it. Old gasoline often causes starting problems, so drain it and refill with fresh fuel. Consult a small engine professional if the carburetor shows signs of varnish after cleaning.

Conclusion

Most Craftsman 150cc no-start problems come down to fuel, spark, air, or choke settings. Work through the checks in order, and most mowers will be running within an hour. If the engine still won’t fire after these steps, a small engine repair shop can diagnose internal issues safely.

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Graham Fisher

About Graham Fisher

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