Most Common Lawnmower Engine Problems

Most Common Lawnmower Engine Problems

Here are some of the most common lawnmower engine problems found and some possible fixes for them!

Mower won’t shut off until you disconnect the spark plug

The way a mower engine works, the spark plug sparks, creating an ignition source, which is the driving force to get your engine to run, no spark=no power.

Usually, when you turn off the key of your lawn mower it shuts the engine off, but other times you may need to resort to removing the spark plug wire to get your engine to stop running.

This could be caused by a variety of things, but two of the most common problems that cause this issue are if the ignition switch connections have gone bad or if the “kill” wire, also known as the ground wire, has become severed or has disconnected from the area that it “grounds” to.

The best way to fix this is to check out the kill wire, make sure it is connected and fully intact, if this looks good, it is time to check out the ignition switch.

To check your ignition switch, you can use an ohmmeter to see if there is any connection between the “S” and “B” terminals. If there isn’t any, the ignition switch is your problem and you will need to replace it to get your mower running properly again.

Mower Starting and then Quickly Dying

If your mower starts and runs a few seconds/minutes and then suddenly dies, it could be one of a multitude of problems.  Often times this problem can be attributed to one of the following:  the carburetor, the fuel cap, the fuel or the spark plug.

The gas that you get from a gas station contains ethanol, which is not good for engines. Keeping this fuel for more than 30 days is not advised, especially if you are using it in a small engine. Using old fuel in an engine can cause the carburetors to get gunked up and function incorrectly.

The first thing you can do is remove the carburetor and clean it. You could do a mild cleaning, such as emptying the fuel out of the carburetor bowl and spraying carburetor cleaner into all of the openings on the carburetor. However, if it is a problem with some of the valves or smaller pieces, you may want to take apart the carburetor completely,  put the big parts in an ultrasonic cleaner to clean them, and then rebuild the carburetor with a new carburetor repair kit so that you can be sure there is enough air and fuel getting into the carburetor.

Another potential cause is the fuel cap. Fuel caps have very small vents on them that allow some air to get into the gas tank, this is vital for proper function.  If the vent is blocked in any way, it could cause your mower to shut off. To see if this is the problem, slightly unscrew your gas tank so that air can get into the fuel tank, then try to run your mower, if this works, you should replace the gas cap as soon as possible.

Finally, it could be the spark plug or the ignition coil. If either are damaged or loose it could be causing the mower to start up and then shut down.  If the spark plug wire is loose or damaged the connection won’t be enough to keep the engine going. To test this you can use a spark plug tester. If the spark plug does not have a visible and strong spark between the electrodes while the engine is cranking you should promptly replace the spark plug.

Mower won’t start

If your mower won’t start at all there are a few things that could be causing this.

Some of the things you can do are:

  • Change the air filter, a dirty air filter can prevent air from getting into the carburetor and the engine won’t start
  • Replace the spark plug, old or damaged spark plugs will not work properly, if there is no spark, there is no power
  • Get rid of any fuel that is older than 30 days and then clean the carburetor, just incase ethanol has caused build up in the carburetors and is blocking vital ports

Usually, doing these things will solve your problem. If these don’t work the problem may just be engine failure and it may need to be taken to a shop to be evaluated and repaired.

Engine cranks, but will not fully start

This is another problem that can be easily fixed, however, if none of these things work, your mower may need to be taken to the shop.

First, you should check the fuel level, if the level is too low the carburetor may not be getting enough fuel, if the fuel level is okay, there is a potential it could be a clog. At this point you should remove the carburetor and clean it, and also check the fuel system for any potential clogs.

Next, you should check the throttle/choke to be sure you have it set in the right position, you can find this information in your owner’s manual.

Finally, the spark plug or disconnected wires could be the cause as it was in previous problems. The spark plug is vital to the engine running and any problems with it could cause a multitude of engine difficulties. Check the spark plug and the ignition wire to be sure they are both properly functioning.

If none of this works, you should call your local small engines repair shop to have it looked at and repaired.

Mower stops mid mow

One of the easiest possible fixes for this problem is to adjust the cutting height of your mower. If you are trying to cut too much grass the mower may stall and shut down as the glass gets clogged up in the deck.

Another fix is to check out the ignition module. Your mower may have a bad coil, especially if you cannot re-start your mower while it is still hot.  If you have to wait for the mower to cool to start it, you should probably replace the ignition coil.

While these are two simple fixes, the problem may be a little more serious such as a shorted out electric fuel solenoid, if this is the case, you are going to need to replace this part. This is a rare case though. You will notice smoke coming from under the hood of your mower if this was to be the cause of the mower stopping after you have been mowing for a bit.


These are the most common lawnmower engine problems that come up with lawn mowers. Never hesitate to consult your owner’s manual or take your mower in to your local repair shop if you do not feel comfortable making any of the repairs yourself. Keeping up with routine maintenance is a great way to help prevent some of these problems, so be sure to follow the recommended maintenance schedule that is specific to your mower, you can find this information in the owner’s manual, so be sure that you take this preventative measure to keep your mower running like new!


I have lost the spark plug for my Frisky Fox( garden fox)wolf 4.5hp lawn mower .
How do I find out what spark plug to get.


It’s good to know that the spark plug could be disconnected or not working if the engine is cracking. I was trying to mow my lawn yesterday, however, my lawnmower wasn’t starting up at all. I’ll have to call a professional to have it fixed before my lawn gets too long.

Taylor Hansen,

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