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- Hey guys, welcome back to my small engine repair channel.
Today I'm going to show you guys the top five reasons
why your lawnmower won't start.
So to get right into this guys,
one of the top five reasons your lawnmower will not start
is because of a bad spark plug.
So because of carbon buildup,
you may have a spark plug that is fouled,
kind of like these ones over here.
You can see this one right here is just full of carbon.
That's why the machine would not run.
And even sometimes if you have a spark plug like this
with a little bit less carbon,
it's still won't work properly.
Now, if you're new working on lawnmowers,
usually the spark plug will be located
at the front of the engine.
Now in this machine here, it's located right here.
Now a good rule of thumb is to replace your spark plug
at least once a year.
And for the price of a spark plug nowadays,
it's worth the investment.
Now, a second reason why your lawnmower won't start
is because of bad gas or a dirty carburetor
caused by bad fuel.
Now here's what can happen to your carburetor
if you leave your lawnmower sitting with old fuel,
it's going to get all gummed up like this.
You can see that the bottom jet here of the carb
is all clogged up with old gas.
You can see there's a film of varnish as well
from that old fuel.
Now, in this case, you might want to try
and clean your carburetor with some cleaner
or the better and most easy solution for most people
would be to just completely replace the carburetor.
So what you can do to try to prevent this
is when you put your lawnmower away for quite a while
is totally drain the fuel from the gas tank.
And also the carburetor if you're able to do that.
If you're not able to do this, you can use a good stabilizer
to keep the quality of your fuel in good condition
in the fuel tank.
Otherwise, if you don't do that,
you're going to end up with a carburetor like this
that most likely needs to be completely replaced.
This is a little more expensive
than if you maintain the machine and drain the fuel
and keep a good stabilizer in it.
And by the way, what I recommend to all my customers
here in the shop is to use a premium fuel with no ethanol.
There's less chance of it going bad
and causing this to your carburetor.
Now, the next reason why your lawnmower won't start
could be because of a dirty air filter
or a dirty fuel filter.
So let's start with the air filter.
If you have a dirty filter like this on your lawnmower,
here's another one here what's going to happen
is your machine won't be able to breathe.
So what's going to happen is your machine will suck up
all kinds of fuel into the engine
because it's choking and it's going to be flooded
and it will not start.
So basically you want to replace your air filter every year.
Here's a clean filter beside the dirty one over here,
you can see there is a gigantic difference
between both of them.
So this filter here can breathe, that one cannot.
If the machine did run with this filter,
what would happen is your fuel consumption
would be very high thus increasing the emissions
going out of your engine as well.
This one here can breathe
so it's going to burn the proper amount of fuel
that the machine should be burning.
So typically I tell my customers,
replace your air filter every year.
If it's really dirty.
For example, if it becomes like this
halfway through the season,
then just change it again to a new one.
If you're using your machines commercially,
then you want to check them every month or less.
Now, the next thing you might want to check
is the fuel filter.
On this one, it's got an inline filter.
So again, I tell my customers to replace your fuel filter
every year on their machines.
Not all machines have an inline filter like this.
Some of them will have a screen inside the fuel tank.
Now if your mower doesn't have a filter like this
and the fuel is not flowing through to the carburetor,
it's more than likely that the screen inside the tank
is clogged.
There's usually a screen right at the bottom
where the connector comes out of the fuel tank.
You can take the tank off, air blow it,
let it dry in the sun if there's moisture,
put it back on and you should not have an issue.
Now on some other machines, like the Honda engines
and different ones.
If you pull the fuel line at the bottom of the fuel tank,
you'll see the fuel filter and you can check
to see whether it's clean or not.
Now these little filters going to fuel tank as you saw
and into the fuel line,
you can air blow that dirt out if you want,
or just replace the filter entirely.
And generally I tell my customers to check this once a year
on their machine.
Now, the next reason why your lawnmower may not start
is because of a bad ignition coil.
So the ignition coil in your lawnmower
is responsible for providing spark to your spark plug.
Now, the ignition coil is positioned
right beside the flywheel under the shroud of the engine.
Now some symptoms you might get with a bad ignition module
is the machine might run when it's cold,
but as soon as it heats up,
it stops running because it's not producing spark
to the spark plug anymore.
So a lot of people call me, they say hey,
my lawnmower's not running,
but I start it up when it's cold, it runs good for awhile.
I run it for about 10 minutes
and then it dies and won't start.
I go back the next day or a couple hours later,
and it starts up and does the same thing all over again.
If that's what you're experiencing with your lawnmower,
you probably have a bad ignition coil.
Now, if you're running across this issue,
sometimes what you can do is when it dies
is take the spark plug boot off, take the plug out,
ground it to the machine
while it's plugged in the spark plug boot
and turn the engine over to see if you have spark or not.
Now, if you have a hard time to do that,
you can always use a spark tester
that you plug in between the spark plug boot
and the spark plug, and just pull it over
without removing the plug and check to see
if the light lights up in the tester.
If the light lights up in the tester here,
you have a good coil.
If it doesn't, that means that your coil is bad
and needs to be replaced.
And it's not that big of a deal
to replace an ignition module.
I do have a video that shows how to do that.
And I'll put the link under the video as well here
so that you can watch it.
Now, the last reason I'll be talking about
why your lawnmower may not start
is because of a sheared flywheel key.
Now the flywheel key is in between the flywheel
and the crank shaft on your lawnmower.
When the flywheel key's good, it lines up perfectly
with the keyway on the crank shaft
and the keyway hole on the flywheel.
Now if the flywheel key is sheared.
You'll notice that it won't line up with the keyway holes
on the flywheel and the crank shaft.
Now, to be able to identify this,
you have to remove the cowling on your lawnmower engine,
and then you'll have to remove the flywheel nut
and the washer to be able to see it like this.
So in this case here, the flywheel key is all lined up
with the keyway holes on the flywheel and the crank shaft.
So it's good, it's not causing any problems.
If it's not lined up, it will cause a problem
because what's going to happen is the ignition timing
will be off with the spark going to the spark plug.
In some cases, your machine may still start
with a sheared flywheel key,
but it's going to run really rough.
Now, usually a sheared flywheel key occurs
if you've hit something hard,
like a rock or a piece of wood, a stump,
and your machine stopped abruptly.
And usually that will cause the flywheel key here to shear.
It is a sacrificial part.
It only costs a few dollars,
but it is very critical to the proper functioning
of your lawnmower.
Again, it provides proper timing for the spark
that goes to your spark plug.
So I do have a step-by-step video
that shows how to replace a flywheel key on a lawnmower.
The link is under the video as well.
If you watch that video, you'll be able to do it yourself
without taking it to a shop.
And you're going to notice
that if you have a sheared flywheel key and you replace it
your machine will run like new again.
So hopefully this video has helped you
to diagnose your machine.
And I hope that the five reasons I showed in the video
are what your problem is.
Look at the links underneath my video,
because I do have other videos that show
how to repair the things I showed in this video.
Again, these are the most common reasons
why machines come in my shop that won't start.
And the same principle can apply to your lawn tractor
and other equipment that you own at home.
Thanks again for watching guys,
please make sure you're subscribed
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Have a great day.
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