How to Fix a Lawn Mower That Won't Start: Complete Troubleshooting Guide

• Check the basics
• Test for spark
• Inspect fuel delivery
• Clean or rebuild the carburetor

In this guide, I’ll show you:

• Check the basics
• Test for spark
• Inspect fuel delivery
• Clean or rebuild the carburetor

The Problem

Your lawn mower’s been sitting in the shed all winter. It’s spring, you’ve got grass to cut, but the mower won’t fire up. This is one of the most common issues I see, and nine times out of ten, it’s fixable with basic tools and a little know-how.

Step 1: Check the Basics

Before you dive deep, verify:

• Fresh fuel - Is the tank empty? Use fresh gasoline, not old fuel from last season
• Oil level - Check the dipstick. Some mowers won’t start if oil is low
• Air filter - A clogged filter can prevent starting. Look at it - if it’s filthy, that’s probably your problem

Step 2: The Spark Test

This is where we determine if you’ve got spark:

1. Remove the spark plug wire
2. Unscrew the spark plug
3. Use a spark plug tester (around $15) to check for spark
4. If no spark, replace the plug with a new one
5. If still no spark, you might need professional service

Step 3: Fuel System Check

If you’ve got spark but no start:

• Drain old fuel - If the tank has been sitting for months, fuel can varnish and clog the carburetor
• Clean the carburetor - This is the most common culprit. Use carburetor cleaner and a small brush
• Check the fuel line - Make sure it’s not kinked or split
• Run fuel stabilizer - For future storage, add this to prevent varnish buildup

Step 4: The Start Procedure

Once you’ve checked everything:

1. Fill with fresh fuel
2. Prime the engine (consult your manual for your mower’s method)
3. Use the choke (usually all the way on if cold starting)
4. Pull the cord firmly and steadily

What If It Still Won’t Start?

At this point, you’ve likely solved it. But if not:

• The compression might be low (professional service needed)
• The fuel pump could be faulty
• Spark plug wire might be damaged

Prevention for Next Season

• Don’t store with fuel in the tank
• Use fuel stabilizer before storage
• Run the engine dry at the end of the season
• Keep the spark plug clean
• Change the air filter yearly

DIY Veteran Tips

One thing I’ve learned over the years is that patience and the right tools matter. Start with the basics, verify each system, and don’t skip the simple checks before buying parts.

For lawn mower repair work, slow and methodical beats rushing — especially when you’re diagnosing an intermittent problem.

Final Thoughts

Most lawn mower repair issues are fixable with a methodical approach. Use the steps above, grab the tools that match your repair, and take your time.

If you work through this guide and still hit a wall, you’ve at least narrowed down the problem — and that’s half the battle with how to fix a lawn mower that won’t start: complete troubleshooting guide.

Creator picks

Tools & products for this job

These are the exact tools from my video list — tested in real jobs, not random affiliate filler.

Garage Staple

Spark Plug Tester

Quick and reliable way to check if your spark plug is firing. Essential for small engine troubleshooting.

+ Instant yes/no spark confirmation without guessing

+ Compact and lives in my mower troubleshooting kit

− Only checks spark — won't diagnose fuel or compression issues

The DIY Veteran's rating

4.8

Price:$5.99

Order now at ›

Digital Multimeter

Essential multimeter for voltage, capacitor checker, continuity, and resistance testing on engines and electrical systems.

The DIY Veteran's rating

4.7

Price:$18.39

Order now at ›

B&S Coil

This coil works with most Briggs and Stratton engines.

The DIY Veteran's rating

4.6

Price:$16.88

Order now at ›

Lawn Mower Won't Start Toolkit

Every tool I reach for when a mower won't fire up — spark testing, fuel checks, and carb work. Matches my YouTube troubleshooting walkthrough.

View 3 products →

As an Amazon Associate, I earn from qualifying purchases at no extra cost to you. Links open Amazon's secure site — we never see your payment info.

Related repair guides

Carburetor Repair

Carburetor Cleaning Guide for Small Engines

Clean and rebuild your carburetor with the right tools and methods to keep your mower running smoothly.

Read guide →