Craftsman M115 Lawn Mower Won’t Start: 7 Causes and Fixes

By Graham Fisher

Updated November 2026

If your Craftsman M115 lawn mower won’t start, the cause is usually one of a handful of simple problems: old fuel, a fouled spark plug, a clogged air filter, a dead battery on electric-start models, or a safety interlock that isn’t engaged. This guide walks you through checking each of those in a logical order, so you can rule things out quickly instead of guessing. Most owners can fix the problem with basic hand tools in under an hour.

Before You Start: Safety Checks

Before touching the engine, make sure the mower can’t move or start unexpectedly. Work on a flat, level surface, and take these precautions every time.

• Disconnect the spark plug wire and tuck it away from the plug so it can’t accidentally reconnect.
• If you have an electric-start model, disconnect the battery’s negative terminal first.
• Let the engine cool completely if you’ve just been mowing. The muffler and cylinder head get hot enough to burn.
• Wear eye protection and gloves when cleaning or working around fuel.

If you smell strong gas, see fuel leaking, or are unsure about any step involving the fuel system, stop and consult a qualified small-engine technician.

Step 1: Check the Fuel and Fuel System

Stale or contaminated fuel is the most common reason a Craftsman M115 won’t start, especially if the mower sat over the winter. Ethanol-blended gasoline can break down within 30 days and leave varnish in the carburetor jets. Many Craftsman owners find that draining the fuel and adding fresh gas solves the problem on the spot.

1. Look at the fuel in the tank. Dark, sour-smelling or cloudy gas should be replaced.
2. Check the fuel line for cracks, stiffness or leaks. Replace any line that feels hard or brittle.
3. Confirm the fuel shutoff valve (if equipped) is open.
4. Drain the old fuel into an approved container and refill with fresh unleaded gasoline. Use gasoline no more than 30 days old when possible.

If fresh fuel doesn’t help, the carburetor may be gummed up. Carburetor cleaning is a common repair, and you can find a step-by-step approach in our article Craftsman Lawn Mower Won't Start: 8 Fixes to Try First.

Step 2: Inspect the Spark Plug

The spark plug is a quick check and a cheap part to replace. A fouled or worn plug will produce a weak spark or none at all.

1. Remove the plug with a spark plug socket and a ratchet.
2. Look at the electrode. A dry, sooty black tip usually means a rich mixture or a dirty air filter. A wet, oily tip suggests oil getting into the cylinder. A white or blistered tip points to overheating.
3. Check the gap with a feeler gauge. Compare it to the gap listed in your owner’s manual.
4. Reinstall the plug, or replace it with the type specified in the manual. Snug it down, then tighten to the torque the manual lists, and reconnect the plug wire firmly.

Step 3: Clean or Replace the Air Filter

A clogged air filter starves the engine of air, which leads to hard starting, rough running or a mower that dies right after it fires. Check the filter housing, typically a cover held by a knob or clips on the side of the engine.

• Foam filters: Wash in warm soapy water, squeeze dry, and lightly oil if the manual calls for it.
• Paper filters: Tap out loose debris. If the paper is oily, torn or heavily caked, replace it.

Replacing a filter is typically a few minutes of work and a good first maintenance step before you dig further.

Step 4: Check the Safety Interlocks

Craftsman mowers include safety features designed to stop the engine when the operator isn’t in position. If one of these systems isn’t satisfied, the engine may crank without starting, or not crank at all.

• Make sure the handle bail (the bar that runs to the handle) is pressed against the handle before pulling the starter.
• On self-propelled models, confirm the drive control is released if the manual requires it before starting.
• Inspect the wiring to the blade brake or interlock switch for loose connectors, rubbed-through insulation or corrosion.

Unplugged or corroded connectors are an easy fix once you find them. Clean the terminals with a wire brush and reseat them firmly.

Step 5: Test the Battery (Electric-Start Models)

If your M115 uses an electric starter, a weak or dead battery may produce a clicking sound, a faint whir, or nothing at all when you turn the key. Battery-related problems are often misdiagnosed as starter failures.

1. Check the battery voltage with a multimeter. A fully charged 12-volt battery typically reads around 12.6 volts or higher at rest.
2. Clean any white or greenish corrosion from the terminals with a baking soda and water solution, then dry thoroughly.
3. Charge the battery fully using a charger rated for its chemistry. If it won’t hold a charge after a full charge cycle, replace it.

Confirm the battery is seated correctly and that the terminal clamps are tight before you blame the starter.

Step 6: Look at the Starter and Recoil Assembly

On recoil-start models, a broken or worn starter rope, a sticking pawl, or a damaged recoil spring can prevent the engine from turning over. Pull the rope slowly and watch the flywheel. If the rope pulls freely with no resistance, the starter pawls may not be engaging. If it feels like the engine is turning but the rope keeps retracting, check the return spring.

Replacement starter parts are common for this model family, and our guide Craftsman M220 Lawn Mower Won't Start: 7 Best Recoil Starter Replacements (2026) covers how to compare options for similar Craftsman recoil assemblies.

Step 7: Check for Engine Compression

If everything above checks out and the engine still won’t fire, low compression may be the issue. Worn piston rings, a damaged valve, or a leaking head gasket can all cause this. A compression tester is the right tool for the job. Readings well below the manufacturer’s specification indicate internal wear and usually mean the engine needs a professional inspection or repair.

Quick Reference: Symptoms and Likely Causes

Common Mistakes

• Skipping the fuel check. Many owners spend an afternoon on the starter before realizing the gas is old.
• Overtightening the spark plug. This can strip threads in the cylinder head, which is an expensive repair.
• Using the wrong oil or fuel mix. Some Craftsman engines require specific oil levels and fuel types. Check the manual.
• Ignoring the choke. A cold engine needs choke, but a warm engine can flood with it engaged.
• Forgetting to reconnect the spark plug wire after maintenance, which leads to a second round of troubleshooting.

Tips for Preventing Future Starting Problems

• Add fuel stabilizer to gas if you store the mower for more than a month.
• Run the engine dry or drain the carburetor before winter storage.
• Replace the spark plug and air filter once a season or as the manual recommends.
• Change engine oil on schedule. Low or dirty oil makes starting harder and wears the engine faster.
• Keep a note of the maintenance you’ve done so you can spot patterns over time.

Recommended gear

A few inexpensive tools make the diagnosis and repairs above much easier.

• Spark plug socket and ratchet: A dedicated socket prevents cracking the plug’s ceramic insulator and makes removal much easier. View on Amazon
• Digital multimeter: Essential for checking battery voltage and testing wiring continuity on electric-start models. View on Amazon
• Feeler gauge set: Lets you measure and set spark plug gap accurately. View on Amazon
• Fuel stabilizer: Helps keep gasoline fresh during storage and reduces varnish buildup. View on Amazon

FAQ

Why does my Craftsman M115 start and then die?

This usually points to a fuel delivery problem or a restricted air supply. Check for a clogged air filter, stale fuel, or a partially blocked carburetor jet. A dirty fuel cap vent can also starve the engine.

How often should I replace the spark plug?

Most manufacturers recommend inspecting the plug each season and replacing it at least once a year or every 100 hours of operation, whichever comes first. Check your owner’s manual for the exact interval.

Can I use ethanol-free gas in my mower?

Ethanol-free gasoline is often recommended for small engines because it tends to store longer and cause fewer fuel system problems. Check your manual for the approved fuel type and any ethanol limits.

Do I need to remove the carburetor to clean it?

Sometimes a carburetor cleaner spray can clear light deposits without removal. Heavy varnish usually requires taking the carburetor off, disassembling it, and cleaning the jets and passages.

Why won’t my electric-start M115 turn over at all?

Check the battery voltage first, then the battery terminals and connections. Also confirm the safety interlock is satisfied and that the key or switch is working.

When should I take my mower to a professional?

If you suspect low compression, internal engine damage, fuel leaks, or electrical problems you can’t trace, a qualified small-engine technician is the safer choice.

Is it worth repairing an older Craftsman mower?

Often yes, since many parts are inexpensive and the engines are generally durable with regular maintenance. If the engine has major internal damage or the deck is badly rusted, replacement may make more sense.

Conclusion

Most Craftsman M115 starting problems come down to fuel, spark, air flow, or a safety or battery issue, and working through them in order saves time. Start with fresh fuel and a clean spark plug, then move to the air filter, interlocks and battery. If the engine still won’t run after those checks, a compression test or professional inspection will tell you whether the problem is internal.

Related reading

• Craftsman M320 Lawn Mower Won't Start: Step-by-Step Fixes
• Craftsman M260 Lawn Mower Won't Start: 8 Causes and Fixes

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.