Mowing is enough of a chore without having to deal with a rough-running,
poor-cutting lawn mower. With just a few bucks' worth of
parts and a couple of hours' work, you can get your lawn mower in
prime shape to start the mowing season. We'll show you how to drain the old
gas, replace the air filter, put in a new spark plug, change the oil and sharpen the
blade—tasks that will keep your gas-powered mower starting easy, running smooth and cutting clean.
Add fresh gas at the start of the season
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Photo 1: Empty out the old gas
Using an old turkey baster, suck old gas from your tank. Squirt it into a
container approved for gas storage and label it as old gas. Refill the tank
with fresh fuel.
Fuel system problems top the list of
lawn mower malfunctions. Many of
these, like gunked-up carburetors,
are often caused by gasoline that's
been left in the mower too long.
Although fall is the best time to take
preventive measures, you can at least get off to a
good start in the spring by replacing
the old gas in your tank with fresh
gas. Photo 1 shows one method.
Gasoline is highly flammable.
Work outdoors or in a well-ventilated
area away from sparks and flame.
Wipe up spills immediately and
store gas in approved sealed containers.
To dispose of the old gas,
call your local hazardous waste disposal
site for instructions.
Most mowers have a mesh screen
over the outlet at the bottom of the
tank. If you can see the screen
through the filler hole, use an old
turkey baster to suck up dirt and
debris that may be covering it.
Video: How to Change Oil in Lawn Mower
Rick Muscoplat, an automotive expert at The Family Handyman, will show you how to change oil in your push lawn mower in our video tutorial. Changing your oil after every 25 hours of use will keep your engine healthy.
Change your oil regularly
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Photo 2: Seal the gas tank
Seal the gas tank by removing the gas cap and covering
the opening with a plastic bag. Screw the cap
back on over the plastic bag.
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Photo 3: Empty out the old oil
Remove the dipstick from the oil filler tube and tip
the mower to drain the oil. Pour the used oil into a
plastic milk jug or similar container and recycle it.
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Photo 4: Refill with clean oil
Refill the engine with clean oil. Most engines require
about 20 ozs. (5/8 quart). Insert the dipstick and check
the oil level. Add oil if needed but don't overfill.
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Photo 5: Alternate oil draining method
Unscrew the plug located on the bottom of the
engine and allow the oil to drain into a pan. Lower
the mower down on its wheels to make sure all the oil
drains. Replace the plug, set the mower on a level surface,
and fill the engine with clean oil through the filler
hole near the base of the engine.
Changing the oil in your lawn
mower takes about 15 minutes and
costs less than $2. That's time and
money well spent considering that
changing oil at the recommended
intervals will greatly extend the life
of the engine. Most engine manufacturers
recommend an oil change
at least every 25 hours of operation
or every three months.
Older mowers have a fill plug
close to the mower deck. Fill this
type until oil reaches the threads of
the refill hole. Two-cycle engines
that use a gas/oil mix for fuel don't
have an oil reservoir on the engine
and don't require oil changes.
Before you drain the old oil, run
the mower a few minutes to warm
the oil and stir up sediment. Then
disconnect the spark plug, drain the
old oil and add new (Photos 1 - 4).
Use SAE 30 W oil (check your
owner's manual). There are two
ways to drain old oil: through the
filler neck (Photo 3) or out the drain
plug in the bottom of the engine
(Photo 5). It's quicker and easier to
drain the oil through the filler neck
if your mower has one. If you have
an older mower without a filler
neck, locate the drain plug on the
bottom of the engine and remove
it to drain the oil. Pour used oil
through a funnel into a plastic milk
jug or other container and label it
Whenever you tip a lawn mower
up on two wheels (Photo 3) to work
on the underside, only lift the side
with the air cleaner. This prevents
oil from running into the carburetor
and soaking the air filter. Also, if
your lawn mower has a fuel valve,
turn it off.
Remember to check the oil level
occasionally between oil changes,
setting the mower on a level surface.
Top it off as needed. Newer mowers
have dipsticks with markings that
indicate when to add oil. Don't
overfill. Check your manual for
instructions to see whether the
dipstick should be fully screwed in
or just set in when you're checking
the level. If you accidentally add
too much oil, follow the procedure
shown in Photos 3 and 5 to drain
Always disconnect the spark plug wire from the spark
plug (Photo 6) before reaching under your mower.
Add pep with a new spark plug
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Spark plug and spark plug wrench
If you're not familiar with them, this is the spark plug and the spark plug wrench.
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Photo 6: Remove the spark plug
Remove the spark
plug wire by pulling
it straight out. If it's
stuck, try twisting it
slightly as you pull.
Wipe off dirt from the
area. Use a 3/4-in. or
13/16-in. deep socket or
spark plug wrench to
unscrew the old spark
plug. Turn the wrench
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Photo 7: Install the new spark plug
Install the new
spark plug by turning
it clockwise two or
three complete revolutions
by hand before
switching over to the
spark plug wrench to
tighten it. Don't overtighten
the spark plug.
plug about a half turn
after it seats to compress
the new washer.
Complete the job by
pressing the plug wire
onto the plug.
Often a new spark plug will make
a big improvement in the way your
engine starts and runs. Spark
plugs are so cheap (less than $3)
and easy to install that it's good
insurance just to replace your plug
every spring. Check your owner's
manual for the correct spark plug,
or take the old plug with you to
the store to match it up.
New spark plugs are factory set
with a .030-in. gap between the
electrodes at the tip of the plug.
Inspect the plug when you buy it
sure there's a gap
about the thickness of
a matchbook cover. If there's no
gap, the plug may have been
dropped and damaged.
Choose another one.
If you don't own a socket
wrench set with a 3/4-in. or 13/16-
in. deep socket for changing the
spark plug, pick up an inexpensive spark plug wrench.
Don't suffocate your mower—change the air filter
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Photo 8: Remove air filter cover
For pleated paper air filters: Locate the air filter near the carburetor. Unscrew,
unsnap or twist off the cover to remove the old filter.
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Photo 9: Replace air filter
Remove the old
air filter and
replace it if it's dirty.
Wipe grass and dirt
from the filter cover
and the mounting
area with a clean
installing the new
filter. Be careful not
to let dirt fall into
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Photo 10: Foam air filter removal
Unscrew or unhook the cover and pull out the
old filter. Wipe the filter cover parts with a
clean rag to remove dirt and grime.
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Photo 11: Prepare new foam air filter
1/4 cup of
clean motor oil over
the new foam filter.
Wrap the filter in a
clean cloth and
squeeze it firmly to
distribute the oil
evenly and remove
any excess. Install
the filter, making
sure the foam lip
covers the top of
the filter holder.
Replace the cover
and tighten the
Air filters are cheap and easy to
replace. Dirty air filters choke the
engine, causing it to run poorly and
lose power. If your lawn is dry and
dusty, check the filter after every
few mowings. Otherwise, check it a
couple of times during the season.
Replace it when it starts to get
plugged with dirt and debris. One
common test is to shine a flashlight
through the filter. If you can't see
the light through the filter, replace it
with a new one.
Most newer mowers have pleated
paper filters that are either flat or
cylindrical (Photo 9),while many
older mowers have foam filters
(Photo 10). Both types of replacement
filters are readily available at lawn mower retailers,
hardware stores and home centers.
Take your old filter along and have
your mower manufacturer's name
and model number handy.
In a pinch, you can wash foam filters
in a solution of laundry detergent
and water and allow them to
air dry. But it's best to just buy a
new one. In either case, saturate the
foam filter in motor oil and squeeze
out the excess before installing it
Video: How to Sharpen a Lawn Mower Blade
A sharp lawn mower blade will help keep your grass healthy. Jeff Gorton, an editor at The Family Handyman, will show you how to sharpen a lawn mower blade so you can keep your lawn in great shape.
Keep your blade sharp for the best cut
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Photo 12: Remove the cutting blade
Disconnect the spark plug wire, turn off the fuel valve and seal the gas
tank (Photo 2). Then clamp a block of wood to the lawn mower deck
with the sharp edge of the blade against the block. Remove the blade by
turning the large nut counterclockwise with a socket wrench.
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Photo 13: Sharpen the cutting blade with a grinder
Sharpen blades with nicks or rounded cutting
edges on a grinder. Hold the blade firmly and tilt
it so the grinding wheel contacts it at the original angle
(about a 30-degree bevel). Move the blade steadily
across the grinding wheel while applying slight pressure.
Dip it in water after each pass to cool it.
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Close-up of ruined blade
This blade is not worth sharpening.
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Photo 14: Sharpen the cutting blade with a metal file
File previously ground or slightly dulled blades
with a 10-in. mill bastard file to hone the edge.
Align the file with the angle of the blade and push down
across the blade. You should feel the teeth cutting the
metal. Maintain the same angle throughout the stroke.
Files cut only on the push stroke. Use a file card to clean
built-up metal from the file's teeth.
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Photo 15: Balance the cutting blade
Balance the blade on a balancing cone ($4 at
hardware stores) before reinstalling it. Working
on a level surface, set the blade on the cone and eyeball
each end. Mark the heavy end. Grind some metal from
the blunt part of the heavy end. Recheck the balance
and repeat until the blade balances. Reinstall the blade,
washer or other parts in the reverse order you
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Close-up of balancing cone
A balancing cone indicates whether or not the blade's been ground evenly.
A sharp blade will make your lawn
mower cut like new. The cleanly cut
grass will look better, and your
mower won't bog down every time
you hit a thick spot. If your lawn is
rough and you mow over rocks and
dirt spots, your blade may need to
be sharpened several times during
the season. Otherwise, once or twice
should be plenty. Keep on top of the
sharpening task by tuning up the
blade with a mill bastard file whenever
it starts to dull (Photo 14).
Once the edge of your blade
becomes rounded or chipped, it's a
lot faster to use a grinder to restore
the edge (Photo 13). Most hardware
stores and lawn mower mechanics
will sharpen your blade for $3 to $5,
but you have to remove it for them.
Use a permanent marker to mark
the bottom of the blade and other
parts like washers and mulching
accessories. Then number them so
they'll be easy to reinstall in the
right sequence and orientation.
Inspect the blade for cracks or
worn-thin areas every time you
sharpen it, paying special attention
to the area at the base of the upswept
section (refer to labeled Close-up of ruined blade in Keep your blade sharp for the best cut section above). Replace
the blade with a new one if the metal
is worn thin or cracked ($10 to $15).
You'll find the best selection of new
blades at a lawn mower service center
or your lawn mower retailer.
It's surprising how quickly you
can put a new edge on a blade with
a sharp file. Buy a 10-in.mill bastard
file ($6) and keep it sharp by
protecting it from moisture and
contact with other tools when
than filing, but
you have to follow
a few safety precautions
and avoid overheating
and ruining the blade.
Wear goggles or a full-face
shield when grinding. Never
wear loose clothes or jewelry that
could get caught in the wheel. Keep
your hands and face out of the path
of the sparks, and make sure there
are no flammable liquids or spilled
It's easy to overheat blades on a
grinder by applying too much pressure
or leaving the blade in one spot
too long. Overheated metal loses its
temper and won't stay sharp. You'll
know if you've overheated the metal
by the change in color from silver to
dull, blackish blue. Proper grinding
technique (Photo 13) and dipping
the blade frequently in water will
help keep it cool.
Always disconnect the spark plug
when you check the blade or
remove it for sharpening.
Some maintenance is best left to the pros
The basic maintenance tasks we
show will go a long way
toward keeping your mower in
good running condition. But there
are two more items that would normally
be included in a professional
tune-up. The first is disassembly and
cleaning of the carburetor and linkage.
This may be necessary if you've
left untreated gas in the tank over
the winter and the lawn mower
won't start or runs poorly. This
repair requires some mechanical
Cleaning grass and debris from the
engine's cooling fins (the cooling fins are
the metal ridges that cover the engine)
is another maintenance task that
should be performed periodically.
On mowers with exposed cooling
fins, this is an easy do-it-yourself
job. Use a stiff-bristle brush to
clean gunk from between the
fins. On many newer mowers,
however, the plastic or metal
covering on top of the engine has to
be removed first, which may also require
disconnecting the fuel tank. Use a flashlight
to inspect the cooling fins under these covers. If they
look clogged, you'll have to decide if you're up to the
challenge or would feel more comfortable letting a pro
handle the job.
Storing Your Lawn Mower for Winter
Gasoline left in your mower
during storage can deteriorate
and leave gum deposits that
clog the fuel system. There
are two storage methods:
completely draining the system
or leaving it filled with fresh,
Most manufacturers of
newer mowers recommend
draining the gas completely.
Do this by opening the drain
valve or drain bolt on the
carburetor bowl and draining
the gas into a container. If your
carburetor doesn't have a drain
valve, check with the manufacturer
or lawn mower repair
center for instructions.
Older lawnmowers with a
foam filter and carburetor that's
screwed to the top of the gas
tank should be filled with
stabilized fuel for the winter.
Purchase a container of fuel
stabilizer, available at hardware
stores, home centers, gas stations
or lawn mower service
centers, and mix as recommended
with fresh gas. Fill the
empty lawn mower tank with
the stabilized gas and run the
mower for about 10 minutes.
Then top off the fuel tank with
stabilized gas and shut the fuel
valve. Check your owner's manual
for storage instructions.