By Graham FisherA Craftsman lawn mower that won’t start after sitting is usually suffering from one of a few predictable problems: stale fuel, a fouled spark plug, a weak battery, or a clogged air filter. In this guide you’ll work through the most likely causes in order, from the quickest checks to the more involved repairs, so you can get the engine running again without guessing. Most people solve the problem in under an hour with basic hand tools.
Before You Start: Safety Basics
Before you touch anything near the engine, disconnect the spark plug wire and move the mower to a flat, well-ventilated area. Keep the engine off while you work on fuel lines, and never smoke or work near an open flame when fuel is exposed. If you have any doubt about handling gasoline or working around the blade, consult a qualified small-engine technician.
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Step 1: Check the Fuel
Old gasoline is the most common reason a Craftsman mower refuses to start after a few months of storage. Gasoline begins to break down within about 30 days, especially in ethanol-blended fuel. The lighter fractions evaporate, varnish forms in the carburetor jets, and the mixture no longer ignites reliably.
How to Tell if the Fuel Is Bad
- The gas smells sour, varnishy or like nail polish remover instead of fresh gasoline.
- The fuel looks dark or has visible debris or water at the bottom of a clear container.
- The engine coughs, sputters or runs rough briefly, then dies.
If the fuel is more than a month old, drain it. Drain the tank by siphoning or by loosening the carburetor drain screw if your model has one, and dispose of the old fuel at a local hazardous waste facility. Refill with fresh regular unleaded gasoline. If you plan to store the mower again, add a fuel stabilizer to the tank before you put it away.
Step 2: Inspect and Replace the Spark Plug
A spark plug that is wet with fuel, coated in carbon, or has a worn gap will prevent ignition even when the fuel system is working. Remove the plug with a spark plug socket and a ratchet.
- Pull the rubber boot off the plug and unscrew the plug counterclockwise.
- Look at the tip. A dry, light tan or gray color is normal. Black, oily or wet tips point to a rich fuel condition, and white or blistered tips suggest overheating.
- Check the gap with a feeler gauge. Craftsman lawn mower engines typically call for a gap around 0.030 inches, but confirm the exact specification in your owner’s manual.
- Clean the plug with a wire brush if it is only lightly carboned, or replace it with a new plug of the same type. Replacement is inexpensive and worth doing once a season.
- Reinstall the plug hand-tight, then snug it with the wrench, and reattach the boot firmly.
Step 3: Check the Battery (Electric-Start Models)
If your Craftsman has an electric start, the battery may be too weak to turn the engine over. Batteries self-discharge during storage, and a battery left unused over winter can drop below the level needed to crank the engine.
- Turn the key or press the start button and listen. A rapid clicking usually means low voltage. A single click with no cranking suggests a poor connection or a dead starter solenoid.
- Test the battery with a multimeter. A fully charged 12-volt battery reads about 12.6 volts or higher at rest. Readings below about 12.2 volts mean it needs charging.
- Charge the battery with a battery maintainer or a slow charger, then try again.
- Clean the terminals with a wire brush and baking soda solution if you see white or green corrosion, and make sure the cable clamps are tight.
Battery problems are more common on mowers stored in cold garages, so keeping the battery on a maintainer through the off-season helps prevent this issue.
Step 4: Clean or Replace the Air Filter
A dirty or damp air filter restricts airflow, which can make the engine flood or run too rich. Many Craftsman mowers use a foam or paper element housed under a cover on the side or top of the engine.
- Remove the cover and take out the filter.
- Foam filters can be washed in warm soapy water, squeezed dry, and lightly oiled with a few drops of engine oil. Let them dry fully before reinstalling.
- Paper filters should be replaced rather than cleaned. Tap out loose debris, but do not wash them.
Step 5: Check the Carburetor and Fuel Lines
Varnish buildup in the carburetor is the most stubborn storage problem. If fresh fuel and a new spark plug did not solve the issue, the carburetor jets may be clogged. Look for these signs:
- Fuel leaking from the carburetor bowl or around the throttle shaft.
- Fuel lines that are cracked, hardened or soft.
- No fuel reaching the carburetor when you check the line at the inlet.
Carburetor cleaning involves removing the bowl, cleaning the jets with carburetor cleaner and compressed air, and replacing the gasket. Take photos before disassembly so you remember where every spring and float goes. If the fuel lines are brittle, replace them with fuel-rated hose of the correct inside diameter.
Step 6: Check the Engine Oil
Low oil can trigger a safety shutoff on some engines, which stops the mower from starting. Check the dipstick or fill cap with the mower on level ground. Add the grade specified in your manual if the level is low. If the oil looks milky or has a gasoline smell, it may be contaminated and should be changed.
Step 7: Check Safety Switches and the Blade Engagement
Most walk-behind and riding Craftsman models have safety interlocks, such as the operator presence bar, the blade engagement switch and the seat switch. A switch that is stuck, misaligned or dirty can prevent the engine from starting. Press each control fully, check the wiring for damage, and clean any debris from the switch housings.
Step 8: Test the Engine With Starting Fluid (Carefully)
Once the fuel, spark, battery and air intake are verified, you can use a small spray of starting fluid to determine whether the engine is getting fuel at all. Spray briefly into the air intake while cranking. If the engine fires and dies, the fuel system is the likely culprit. If nothing happens, return to the spark and compression checks. Use starting fluid sparingly, because overuse can damage the engine.
Troubleshooting Checklist
| Symptom | Most Likely Cause | First Fix |
|---|---|---|
| Cranks but won’t fire | Stale fuel or fouled plug | Drain fuel, replace plug |
| Rapid clicking, no crank | Weak battery | Charge or replace battery |
| Single click, no crank | Loose cable or bad solenoid | Clean and tighten terminals |
| Floods or smells of fuel | Dirty air filter or carburetor | Clean filter, check bowl |
| Fires briefly, then dies | Fuel delivery or clogged jets | Clean carburetor, check lines |
| No response at all | Safety switch or interlock | Check seat, blade and bar switches |
If you are still stuck after these steps, the problem may be a different issue entirely. Our guide to Craftsman Lawn Mower Won't Start: 8 Fixes to Try First covers additional checks, and Lawn Mower Won't Start After Winter: 7 Fixes That Work goes deeper into off-season recovery.
Common Mistakes
- Adding fresh fuel on top of old fuel. Always drain stale gas first. Mixing it only dilutes the problem.
- Overusing starting fluid. Repeated sprays can wash oil off cylinder walls and damage the engine.
- Ignoring the battery charger. A dead battery in storage is one of the most preventable causes of no-start.
- Cleaning a paper air filter with water or solvent. This destroys the element. Replace it instead.
- Skipping the gap check on a new plug. Plugs can arrive with the gap set incorrectly.
- Forgetting the spark plug boot. A loose boot causes intermittent no-spark conditions that are hard to diagnose.
Tips for Preventing the Problem Next Season
- Add fuel stabilizer to the tank before storage and run the engine for a few minutes so it reaches the carburetor.
- Alternatively, run the carburetor dry by letting the engine stall out of fuel before storing it.
- Change the oil and replace the spark plug at the end of each mowing season.
- Store the mower in a dry location and keep the battery on a maintainer if it is electric-start.
- Keep a small log of maintenance dates so you know when each service was last done.
Recommended gear
A fuel stabilizer is the single most useful addition for storage. Products such as STA-BIL Storage Fuel Stabilizer are widely used for this purpose and are designed to keep gasoline fresh for extended periods. View on Amazon
A battery maintainer keeps the battery topped off during the off-season without overcharging it. The NOCO Genius1 is a commonly recommended unit for small batteries. View on Amazon
A spark plug socket with a rubber insert holds the plug securely during removal and installation, which helps prevent damage to the ceramic insulator. View on Amazon
A feeler gauge set lets you check and adjust the plug gap accurately before installing a new plug. View on Amazon
FAQ
How long can gasoline sit in a Craftsman mower before it goes bad?
Gasoline can begin to degrade within about 30 days, particularly if it contains ethanol. Using a fuel stabilizer can extend its usable life to several months or more, but the safest practice is to drain or use up fuel before long storage periods.
Can I use starting fluid to get my mower running?
Starting fluid can help confirm whether fuel is reaching the engine, but it is a diagnostic aid rather than a fix. Use it sparingly, and address the underlying fuel or ignition problem so the engine can run on its own.
Why does my mower start and then stall after a few seconds?
This usually points to a clogged carburetor jet, a restricted fuel line, or a dirty air filter. Stale fuel can also cause the engine to run briefly and then die as the remaining fuel in the bowl runs out.
Do I need to replace the spark plug every year?
Replacing the spark plug once a year is a common and inexpensive maintenance step. Owner’s manuals typically recommend checking the plug at least annually and replacing it when the electrode is worn or the deposits cannot be cleaned.
My battery is new but the mower still won’t crank. What now?
Check the cable connections for corrosion and tightness, then inspect the starter solenoid and wiring. A new battery will not help if the connection path is broken. A technician can test the starter circuit if the simpler checks do not reveal the fault.
Should I take my mower to a repair shop?
If you have worked through the checks above and the engine still won’t start, or if you are uncomfortable with carburetor disassembly, a qualified small-engine technician can diagnose the problem quickly. Consult a professional before attempting repairs on engine internals.
How often should I service a Craftsman mower?
Most owners service the oil, air filter and spark plug at least once per season, with more frequent checks if the mower is used heavily. Follow the interval listed in your owner’s manual, since requirements vary by engine.
Conclusion
A Craftsman lawn mower that won’t start after sitting almost always comes down to fuel, spark, battery or air intake. Work through the checks in order, starting with fresh fuel and a clean spark plug, and most mowers will fire up within minutes. A little preventive care before storage will make the problem far less likely next spring.
Related reading
- Lawn Mower Won't Start After Sitting: 8 Causes and Fixes
- How to Fix a Lawn Mower That Won’t Start After Winter
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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.
