Lawn Mower Won’t Start – Quick Troubleshoot & Fix Guide

Gasoline lawnmowers have a lot of moving parts which can make them fickle to start sometimes. Especially if it’s an older gasoline lawnmower. If you have a lawnmower that suddenly won’t start, or refuses to start after a long hard winter, there are a few troubleshooting things you can try.

Some Of the Most Common Problems & Fixes Are

  • Dirty air filters  – need to replace
  • Grass is too tall for the mower to handle
  • Dirty spark plugs and cables
  • Too much debris or lawn clippings built up underneath
  • Dull, damaged or loose blades
  • Main jet isn’t clean
  • Carburetor is corroded with chalky white stuff
  • Carburetor is flooded with gas. Wait a few minutes to let gas evaporate
  • Low oil levels, or oil needs to be replaced
  • Run out of gas or battery – yes, it happens!
  • Old gas that was sitting too long
  • Loose plug (for electric mowers)
  • Throttle control should be set to full revs position
  • Starter rope isn’t jammed
  • Diesel gas was used instead of regular gas
  • Use the choke if manual
  • Water in the fuel tank
  • Try fuel stabilizer if it starts and then dies

Determining If It’s A Minor Mechanical Problem

Little things can sometimes cause big problems when you try to start a lawnmower. Before jumping into major issues like a carburetor and spark plug problems, you should try some of the following minor mechanical things.

Take a close look at the throttle control cable, follow down from the handle to the connection with the lawnmower engine. Keep an eye out for damaged, pinched, or compressed somewhere along the line. This is even more likely to be an issue for lawnmowers with collapsing handles for compact storage.

During your visual inspection keep an eye out for other things like grass clippings clogging around the air filter or the breather holes in the gas gap. Even a little debris in the fuel-air system can block combustion. Also, keep an eye out for any rusted bolts or corrosion around moving parts like the throttle linkage. Sometimes a little penetrating lubricant spray on a rusted throttle cable connection will help free things up.

Check The Lawn Mower’s Fuel Tank

Since they are only used occasionally, lawnmowers tend to have fuel sitting in the tank. As days and possibly weeks go by tarnish from low-quality gasoline can sometimes start to buildup in the tank. If you also tend to refuel your lawnmower in the middle of a cutting session, dust, grass pollen, and other tiny particles can invade the fuel tank.

As these deposits build up they can potentially clog the fuel system. This is even more likely to be an issue if you accidentally ran it out of gas recently, as the debris can be sucked into the fuel system.

Ideally, you should be able to see the clean bottom of the lawnmower’s fuel tank by shining a flashlight into it. If you see debris, you might want to use a gasoline siphon kit to draw the dirty or degraded fuel out and replace it with fresh, high octane gasoline.

Check The Battery On A Riding Lawn Mower

If you have a riding lawnmower, it likely relies on the battery to start the combustion process. If the battery is old, corroded, or frozen over the previous winter it might not have sufficient charge to start the lawnmower’s engine.

If you don’t have a battery test or multi-meter to give you an accurate reading, there are still ways to determine if the battery is very low or dead. Turn on the headlights. If they don’t light or they look orange, then chances are the battery doesn’t have enough charge to start the engine. Another sure sign of a battery problem is clicking when you turn the riding lawnmower’s key.

If it’s just a matter of the battery running low from disuse or it’s near the end of its life but is still functional, you might be able to jump-start it just like you would a car with a flat battery.

Check The Battery Terminal For Corrosion

If your riding lawnmower has a lead-acid battery, the electrochemical process it uses can cause corrosion on the red, positive battery terminal and the connection hardware. This usually looks like a white powdery substance that might have tints of gray, blue, and green.

If you do happen to see some, you should clean it off with a toothbrush and some paste made from baking soda and water. Once it’s been thoroughly cleared away you can try jump-starting the riding lawnmower or recharging the battery with a standard battery charger.

Check The Lawn Mower’s Air Filter

Both riding and walk-behind lawnmowers need air to maintain combustion. Cutting grass can produce a lot of dust and other airborne debris to build up around the air filter. Left unchecked the air filter can clog to the point where the proper fuel-air mixture can’t be maintained in the carburetor or ignition chamber.

Taking the air filter out and giving it a blast of canned air or an air compressor to remove any dust might be just the thing. As long as you have the filter out, look down the throat of the air intake. If you see anything caked on the sides, give it a good wipe with a clean paper towel.

Major Problems That Can Prevent A Lawn Mower From Starting

If you’ve checked through the simple things, then it’s time to roll up your sleeves and take a look at more major issues like the carburetor and the spark plug.

Diagnosing A Lawn Mower Carburetor Problem?

Most gasoline-powered lawnmowers have a carburetor which acts as a combustion chamber where the spark from the spark plug ignites the fuel to air mixture. The expanding gasses then push the pistons.

It’s possible for residue from low-quality fuels, improperly mixed oil, debris from the fuel tank, and dust that passes through the air filter to gum up the carburetor. As it builds up, you’ll likely notice performance issues with the lawnmower’s engine as it gets harder and harder to start or bogs down in thick grass. At a certain point, the carburetor will get so gummed up that it simply won’t fire.

At the same time, carburetor residue can also influence the performance of the spark plug. If you’ve been using low-quality fuel, not cleaning the air filter, and occasionally running the fuel tank out, you might be looking at a double-whammy of both carburetor and spark plug problem.

You can shine a flashlight down the throat into the carburetor and you see if there’s any corrosion or obvious residue. If you see a little, but not a lot you might be able to clean it with some carburetor cleaner spray. The instructions for the brand you choose will be printed on the label.

Diagnosing A Bad Spark Plug

A spark plug is surprisingly precise for something so simple. If a connection is loose or damaged it impede the spark. Spark plugs have a limited lifespan, so sometimes one can give up on you all on its own. Though a clogged carburetor will hasten it’s death or increase corrosion and residue problems, which can prevent a spark from developing on the spark plug leads.

If you’ve been dealing with a gummed up carburetor, you might want to just be proactive and replace the spark plug while cleaning the carb. They’re relatively inexpensive. Though you will need a special torque wrench, which you can buy at any automotive store. That way when you replace the spark plug you’ll tighten it the exact degree recommended in the lawnmower’s owner’s manual.

 

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