21 Tips For Servicing A Petrol Lawnmower.
I truly believe that with the correct maintenance a quality petrol lawnmower can last the full lifetime of the owner.
There are many things you can do to extend the life of a petrol lawnmower and things you should do at the end of the cutting season.
Most of my 21 tips can be undertaken without any special tools and will go a long way to maximising the life and performance of your lawnmower.
In fact, you could probably do most of them in under 5 minutes!
1.Service Once A Year
When you purchase a petrol lawnmower it generally runs perfectly well for the first couple of years.
After this time cables begin to stretch, blades become dull and the carburettor may need servicing also. After the first couple of years of hopefully trouble-free mowing, I recommend following these 21 tips to keep your lawn mower engine and cutting deck in good working order.
2. Fit A New Spark Plug
This isn’t essential every year but it’s at least a good idea to remove the spark plug and clean it off. While the spark plug is removed check the gap is correct according to your operator manual.
Removing the spark plug also means it won’t become seized in the engine.
Be sure not to overtighten the spark plug when replacing as it’s possible to close the spark plug gap accidentally.
I usually hand tighten the plug and then slightly tighten further with a spark plug socket.
I always use NGK spark plugs. I have repaired dozens of lawnmowers for profit that wouldn’t start because of a poor quality spark plug.
Visit the recommended products page for more information on service items.
Here’s a video playlist from my Youtube channel that covers lots of servicing and repairs on petrol lawnmowers.
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3. Wire Brush And Paint The Underside Of The Cutting Deck
I’ve lost count of the number of times I’ve removed a really good lawnmower engine from a rotten lawnmower deck. I believe this is the number one reason people eventually replace their lawnmower.
Remove the spark plug before doing any maintenance or repairs on any type of lawnmower.
Never tip a lawnmower completely over. Tip the lawnmower carburettor side up and lean it against a fence or wall at 45-degree angle with the exhaust facing down so you can get underneath (or ask a really good friend to hold it for you!)
If your lawnmower has a self-drive on then go ahead and remove the blade and belt guard cover to access the underside of the cutting deck.
Take a wire brush and remove all the grass that has managed to attach itself to the underside of the cutting deck. Occasionally I use a pressure washer to do this also.
Grass usually finds it’s way to the underside of the deck when you cut wet grass. Try and avoid doing this if possible in the future.
I like to paint the underside of the deck every year when the cutting season finishes. I usually use Hammerite smooth paint.
I do strongly advise taking the time to do this it will save your deck from rotting long before the engine wears out.
4. Change The Oil
Changing the oil can once again mean tipping the lawnmower up to drain out the oil. I hate doing this.
Often I have won lawnmowers on eBay and Facebook marketplace to repair for profit that the previous owner tipped completely over to drain the oil out!
It always amazes me when the seller announces he simply tipped it over to change the oil and now it won’t start!!
The best way to change the oil on a petrol lawnmower is with an oil extractor.
I usually run the lawnmower for a few minutes to warm up the oil then remove the spark plug and raise the front of the deck slightly to help the oil run to the back of the engine where the oil dipstick is.
Next, I insert the suction hose from the oil extractor into the sump, activate the extractor by pumping it and all the oil is cleanly and completely extracted into the oil extractor.
Oil can and should be disposed of correctly and using an extractor helps you to do this. I regularly take mine to the local tip/garbage disposal and recycle it there. Be sure to use the correct oil for your lawnmower as specified by the manufacturer and never overfill.
Check the level on the dipstick carefully. Most lawnmowers use SAE 30 oil as it’s designed to last longer at higher temperatures.
5. Sharpen The Blade
The easiest way to sharpen a blade is it to remove it and take it to your local lawnmower dealer. They will be able to determine whether the blade needs sharpening or replacing.
Sharpening a blade can be done manually by taking a file and simply sharpening the blade by hand.
A professional lawnmower service centre will sharpen the blade on a bench grinder following the natural angle of the cutting blade.
They will also balance the blade making it evenly weighted.
The angle of a sharpened blade is important as this provides enough uplift for the trimmed grass to be collected in the grass box.
Having the blade balanced can help eliminate vibration throughout the lawnmower. Price up sharpening the blade and purchasing a new one.
Never run a lawnmower with an incorrect or damaged blade.
6. Check The Blade Adapter
A lawnmower blade usually has 2 holes near the centre. These two holes should align with 2 notches on the blade adapter.
Check to see if the blade is correctly set on the adapter and everything lines up. If it doesn’t then replace the blade adapter.
7. Tighten Your Lawnmower Wheels
Lawnmower wheels often have wheel trims attached. Take a flat-headed screwdriver and remove the trims. Tighten all the wheels once a year and make sure there is no excessive play in them. Also, make sure there is plenty of tread on the wheels or tyres.
8. Service The Carburetor
If your lawnmower is starting and running perfectly well then there is no need to service the carburettor.
If you are experiencing hunting or surging problems, white smoke, or startup problems then I suggest servicing the carburettor.
You can find lots more information on this subject by visiting my youtube channel listed on the website menu.
Also, check out this article which covers various carburettor servicing
Here’s a video on how to replace 2 different types of carburettor.
9. Drain And Clean The Petrol Tank
The best way to eliminate any problems with the carburettor is to make sure the petrol and petrol tank is clean.
Each year drain out all the remaining fuel at the end of the cutting season.
I like to remove the petrol tank from the lawnmower and, once dry blow it out with an air compressor or a can of compressed air.
This saves any rust, dirt or debris being transferred down the fuel lines and into the carburettor.
10.Clean The Cooling Fins
I’m often asked by my youtube subscribers why does my lawnmower cut out after a few minutes when it gets hot. (Often it won’t restart)
Most lawnmowers have cooling fins on and with poor maintenance, they all become clogged.
Remove the starter recoil cover and take a look around at the cooling fins. Remove any dirt with a stiff brush or an air compressor.
When engines overheat they stop working. Having clogged cooling fins causes this to happen a lot.
11. Adjust The Overhead Valves
If your lawnmower has an overhead valve set up you may need to adjust the valves from time to time. If your lawnmower starts easily and runs well then skip this procedure.
To set lawnmower valves take a look at the video from my Youtube channel below
12. Tighten All Your Lawnmower Handles
Be sure to tighten all possible parts of the lawnmower handles especially where the handle connects to the lawnmower cutting deck.
Having loose handles can put more strain on the deck and eventually cause the weld on the deck to split.
Take a few minutes to tighten everything up. I often find after a full cutting season these parts have started to make there way loose!
13. Clean Or Repair The Air Filter
This tip is super quick and easy, however, it’s incredibly important. The last repair you really want to do is service the carburettor.
The air filter is designed to catch any dirt to eliminate this happening. You can clean an air filter using some old fuel and once dry smear a very light covering of oil on the outer side of a sponge filter.
Replacement is very cheap and my preferred option.
14. Clean The Kill Switch Or Check The Microswitch.
Petrol lawnmowers either have a kill switch or microswitch fitted. If either become faulty then your lawnmower will not start.
Take a look at this video from my youtube channel on checking a kill switch
Take a look at this video for checking a microswitch.
Make sure the kill switch is clean and there is a visual disconnection when operating the safety lever.
15. Check The Condition Of The Starter Recoil Rope
Check the condition of the starter recoil rope. If it looks frayed you may want to replace it.
This is not too difficult to do.
Most people wonder how much starter rope they will need to replace the old one and also how to do the repair at home.
It’s fairly straightforward but having a clamp can be useful.
You can read a detailed article here.
Here’s a video of how to replace a lawnmower pull cord.
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16. Cable Lubrication
It’s not easy to lubricate an entire lawnmower cable. It is, however, possible to put a few drops of oil on any visible parts of the cable that move.
This will only take seconds to do and could save you having to replace a snapped or damaged cable in the future.
17. Take A Photo Of Your Lawnmower Service Ticket
Take a look around your lawnmower deck. It should have a rectangular service ticket on with all the details of your lawnmower.
This ticket gives you the exact code for your lawnmower plus the manufacturer’s name and manufacturers date of production. Take a photo of the ticket with a digital camera or mobile phone and make a back up of it.
User manuals tend to go missing and if the service ticket gets damaged with fuel or fades over time you will have a difficult time locating spare parts.
18. Check The Throttle Cable Adjustment.
If you have a petrol lawnmower that doesn’t have a primer bulb then it’s a good idea to check the set up of the throttle cable. On many mowers, the throttle is also connected to a butterfly choke inside the carburettor.
Take off the air filter and ask a friend or handy helper to operate the throttle lever on the handle.
Looking past where the air filter was you will see a butterfly valve. This is the lawnmower choking mechanism that’s used when starting a lawnmower. When the throttle is on idle, the valve should be closed almost all the way.
When the throttle lever is moved to full speed the valve should open all the way to allow full speed.
If this is not the case you may have starting issues from cold or the lawnmower will not be running at full capacity.
Take a look at where the throttle cable runs underneath the air filter box and carburettor. There is usually a screw that sets the positioning of the cable. Loosen this screw and try moving the cable to where the butterfly opens and closes fully when operating the throttle.
You will need to loosen the cable screw move the cable and retighten the screw it to do this.
This is how you set the throttle on a lawnmower with a butterfly choke mechanism.
19. Check The Drive Belt
If your lawnmower is a self-drive model you will need to remove the belt guard and inspect the belt.
It’s amazing how much grass can accumulate behind the belt guard. The last thing you want is the belt being dragged off because of this and being cut into tiny pieces by the blade!
Remove the belt guard and if the belt guard cover is attached by a little screw as well as a bolt consider changing this screw from time to time. I’m mentioning this as this little screw can be a real pain to undo once it rusts.
If you struggle to remove the screw then clean it off with a wire brush and spray it up with some penetrating fluid before rounding it off.
One great tip for removing this screw is to use an impact screwdriver. I do this a lot. I don’t hit the impact screwdriver in the traditional way I just find with the extra weight of the screwdriver I can get enough turn to eventually undo it.
Check the drive belt for cracks or tears and make sure if the belt has teeth that none are missing or the belt has become thin and slack.
20. Check The Transmission Box
The transmission box for a self-drive lawnmower is usually situated near the back of the lawnmower. Take good luck around the self-drive box and remove any grass, sticks or nests!
If the operating lever to the back of the transmission box is obstructed you will have a problem with the self-drive not operating.
You can sometimes access the transmission box by liting the grass box deflector up and removing a square plastic part from the back of the lawnmower.
Use a long piece of wood to keep the grass box deflector out of the way by placing it across the handle horizontally.
Here’s a video on lawnmower transmissions
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21. Check The Primer Bulb
If your lawnmower uses a primer bulb to start the engine then take a look around to check for any signs of damage.
If a primer bulb is split it will not deliver fuel to the carburettor and you will have starting issues.
Just a note on primer bulbs, be sure to buy genuine parts.
I have tested aftermarket primer bulbs and they split easily and perish quickly, especially if your lawnmower is stored outside or somewhere with low temperatures.
There are lots of ways you can maintain a petrol lawnmower. I like to do one overall service at the end of each cutting season.
This way my lawnmower goes away clean and tidy with no fuel going stale and it’s ready to go when the new cutting season comes around.
Paying for a petrol lawnmower service really is quite expensive, however, if you aren’t willing to do the work yourself I do recommend having it serviced by a local dealer when necessary.
It will no doubt save you money in the long term especially if you have one of the higher-priced lawnmowers.
Always try to use genuine parts and service your lawnmower once a year.
- If you decide to only do one of the 21 tips listed be sure to clean the underside of your lawnmower deck. This really will help extend the life of your lawnmower. Having the blade sharpened each year will make a massive difference as well.
Feel free to check out my recommended products page for all your spare parts and service items https://repairlawnmowersforprofit.com/recommended-products/
Take a look at my guide to repairing lawnmowers for profit https://repairlawnmowersforprofit.com/how-to-make-money-selling-lawnmowers-my-complete-guide/
I really do hope this article helps maintain and service your lawnmower over many years to come.