My Lawn Mower Keeps Shutting Off? Learn How to Fix Here!

If you are encountering the frustrating scenario of a lawn mower that will start, but not stay running, fret no more, you've come to the right place to fix a lawn mower that keeps shutting off! This situation can usually be attributed to a fuel delivery problem, and the good news is, the fact that your lawn mower starts, normally confirms you have the necessary spark, and engine health to get your mower running reliably again. Knowing this can help you pinpoint the source of your frustrations much sooner. Let's begin our troubleshooting guide with the obvious first! Your gas cap!

Locations of gas cap and fuel tank

A Faulty Gas Cap

Your lawn mower's fuel system needs to be vented in order to regulate the pressure differences between the surrounding air, and the air within the fuel delivery system of your lawn mower. Air must be allowed to enter the gas tank to account for the space created by the consumed gasoline. To put it simply, pressure differences (areas of high and low pressure, and airs' natural tendency to want to balance or equalize, is what allows gravity fed small engine equipment to be fed the proper mixture of air and fuel via the carburetor. When this vent is obstructed, a vacuum is created and it prevents fuel from flowing into the carburetor, which is necessary in order for the equipment to run. A quick test to diagnose this issue is to run your lawn mower until it dies or shuts off. Then remove the fuel cap, and listen for a whooshing noise, indicative of a pressure build up within the tank. This vacuum is preventing the necessary free flow of gasoline into your engine. If possible, look for a small opening in the cap to clean, or replace the cap if faulty.

A Dirty Carburetor

If you are unable to resolve the issue with removing the gas cap, the next logical part to investigate would be the carburetor. It is best to refer to your machine's service manual for instructions on how to properly overhaul and clean your carburetor. If this is not available, please refer to our post on how to clean your carburetor found here: Learn How to Clean Your Carburetor and Get Your Mower Running Again! In essence, a tear down and thorough cleaning of your carburetor should clear out any potential blockages that may have formed in your machine due to fuel contaminants or the breakdown of fuel. Be sure to snap a reference photo on how the carburetor's linkages are situated for future reference prior to disassembly! This makes reassembly all the more easy. Pro Tip: If during the carburetor cleaning process you discover black debris or what look like small black specks, this is a tell tale sign that the internals of your fuel line are collapsing and are potentially clogging the carburetor. The fuel line would need replacing in this scenario.

Look to disassemble the carburetor for a thorough cleaning

Fuel Line/Fuel Filter Obstruction

Inspect your fuel line (if your mower has one,) for cracking. Inspect inside the gas tank for debris build up. Pay particular attention to the lowest point of the gas tank. If your lawn mower is equipped with a fuel strainer, ensure it is not obstructed or collapsed, preventing the flow of gasoline from the fuel tank into the fuel line and eventually into the carburetor. Pro Tip: Inspect the flow of gasoline from the fuel tank to the outlet of the fuel line (where it connects to the inlet of the carburetor.) Fuel should flow easily, and the flow of fuel should be roughly equal to the inner diameter of the fuel line, ensuring good flow of fuel is present. If a mere trickle or no fuel flows, investigate the complete path of fuel flow for an obstruction.

Stale/Contaminated Gasoline

If the age of the gasoline cannot be verified, it is best to safely drain and replace with fresh gasoline. Always tilt your lawn mower with the carburetor facing up to prevent potential issues related to oil and gas seeping into places it shouldn't! Refer to our post here Why Won't My Push Mower Start? Solution: Mind your Gas! to learn about why and how you should properly manage your gasoline for best results. Stale gasoline forms a varnish and can plug up the small, intricate ports of the carburetor. Prevent all these headaches by ensuring your using fresh gasoline only.

Other Less Likely Causes Worth Mentioning

A fouled, or incorrectly gapped spark plug, a excessively dirty air filter obstructing the necessary flow of air into the engine or an intermittent spark issue can also cause a lawn mower to eventually die after a few minutes. Remove spark plug and visually inspect its electrode tip. Remove the air filter housing and inspect the air filter. An intermittent spark issue can be caused by a failing ignition coil or faulty wiring. Inspect for tears in wiring from the ignition coil to the kill switch wire and the spark plug wire. These openings in the wiring can cause the necessary current flow to short out on nearby metal.

If you found this post helpful consider enrolling in our free Online Program designed to transform novice lawn mower operators into knowledgeable and independent troubleshooters, and maintainers of their own equipment! Avoid the expense and hassle of untimely breakdowns! All that is required to enroll is an email, and it is completely free of charge! Click here to be directed to the enrollment page: Online Program

Never the Norm!