How to service and drain a petrol lawn mower

Petrol lawnmowers are known for their unbeatable cutting performance, and can have you finishing off even the largest of lawns, with the most overgrown grass, in no time at all.

There is a catch though. To keep your petrol lawn mower performing at its best, you need to take care of it, just like you would a car, motorcycle, or any other petrol driven machine, and that means regular services.

But don’t worry, you don’t have to fork out for someone else to service your petrol lawnmower like you do your car, you can actually do the job yourself, at home, and with only a few basic tools.

How? Well, that’s what this article is all about, and by the time you finish reading, you will know exactly how to service and drain a petrol lawnmower.

Why do I have to service my petrol lawnmower?

Petrol lawnmowers are not the cheapest of tools, and to ensure that you get your money’s worth, you need to keep them working optimally, and the only way to do that is to service them. Otherwise get yourself some sheep 😀

Now, I’m not saying that you have to give your petrol lawnmower a full service every time you use it, and some maintenance can be carried out at longer intervals than others, but what I am saying is that with regular services and proper maintenance, your petrol lawnmower should last you for not just years, but decades. How’s that for a reason?

How often should I service my petrol lawnmower?

This all depends on how much use and/or abuse the machine is getting, but I’ll point out a couple of things for you. Firstly, if you have a brand-new petrol lawnmower, you shouldn’t have to service it for the first year, except maybe draining the petrol and changing it. The better quality your lawn mower the less you’ll need to service it. Here’s a guide to avoiding costly mistakes buying a petrol lawn mower.

After that, a good full service once a year, plus some minor maintenance here and there as any issues pop up, will suffice.

How to drain a petrol lawnmower

One of the most important parts of a good service is to drain the petrol tank and clean it out as well as you can. The reason for this is that any old fuel can separate in the tank, or debris such as rust can mix in with the old fuel, and then these get passed into the carburettor, where it can cause a lot of damage. Here’s how you do it:

1. Make sure the lawnmower is on a flat surface, and if your model has parking brakes, check that they are activated.

2. Keep the lawnmower in the upright position, and never tip it on its side or upside down, or this will cause all sorts of problems because of fuel and oil leaking into places it shouldn’t be.

3. For safety reasons, unplug the spark plug from your lawnmower. This is very easy to do, and only requires you separate the wire and cap. If you are doing a full service, you should just go ahead and use a spark plug spanner and remove the plug altogether.

4. The next step will depend on what type of petrol lawnmower you have. Look to see if your model has a fuel line that connects the carburettor to the fuel tank. If it does, then all you need to do is find an old plastic tub or bucket to catch the old fuel in, and then remove the fuel line. Take a look at this video to be sure:

If you don’t see a fuel line like this, then it’s a little trickier, but still fairly simple. You will need to use a specific tool for the job though, and that tool is a petrol syphon. Basically, you pop one end of the syphon into the tank, and the other into a plastic container, wriggle and shake the petrol syphon around a bit until it starts pumping the old fuel out.

5. After you have drained the majority of the petrol out of the tank, you will probably still notice some in the bottom, so use some old rags to soak up the remnants.

6. If you really want to ensure that all the old fuel is gone, add some new fuel and move it around for a little while before removing it again like you did with the old fuel. This should ensure that all the old petrol has been completely removed.

7. You can now either wait for the tank to dry out, or remove it and use an air compressor to blow dry it. Once dried, re-attach the tank, fuel lines, spark plug, etc.

8. The last step is to clean out the carburettor. To do this make sure you have a lot of oil in the mower, and then start it up and let it tick over for a while until it stops.
Once this is done, you can refill the tank with fresh fuel and again, let her run for a while.

9. The last step is to give yourself a pat on the back, and then go and have a well-earned cuppa.

Other things to service on your petrol lawnmower

1. As already mentioned, it’s a good idea to change your spark plugs when you drain and change out the fuel, but you don’t have to wait for this. Changing spark plugs is a very easy job and only really requires the right kind of spanner. Locate the spark plug, remove the wire and cap, and unscrew it. That’s all there is to it really.

When replacing the spark plug, be careful not to over tighten it or it can cause problems with staring up the lawnmower.
Sometimes, the spark plug will just need cleaning, but even if you do need to replace it, they are relatively cheap to buy.

2. Keep the cutting blade sharp. The best way to do this is to get yourself a good set of safety gloves, then unscrew the bolt in the centre of the blade and remove it. Once it’s removed there are a number of ways you can sharpen the blade, such as with an angle grinder or a metal file. You could always take it to the nearest workshop or garage and get someone to do it for you too. It wouldn’t cost very much and only take a few minutes.

3. Check the air filter. Your lawnmower will come with instructions on where to find and how to remove that specific air filter, and you should do so at least once a year. The air filter might only need cleaning, and this is easy to do, but for best results, I would just replace it. A clean air filter means a healthier carburettor.

4. One thing that is often overlooked is just keeping the underside of the lawnmower clean. When left to fester, debris can cause rot and rust, and ultimately stop the machine from functioning properly.

The best thing to use is wire brushes, and make sure you really get rid of old, stuck on grass and dirt, and any other built-up debris. If you’ve had the lawnmower for a number of years, it might be a good idea to give the underside a new lick of paint after you’ve cleaned it.
Always make sure you have disconnected the spark plug before doing any kind of work on the underside of the lawnmower.

5. Most lawnmowers have a drainage plug that you can simply unscrew and let the oil drain out into a container. However, if your model doesn’t, you can change the oil by using an oil extractor or oil syphon. Don’t ever tip up the lawnmower if it is avoidable for the reasons, we explained earlier.

6. Other little jobs you can do in your yearly service are to check or replace the starter pull cable, check the wheels and tighten them if necessary, and check for debris around the transmission box.

There you have it, all you need to know about how to service and drain a petrol lawnmower. Go through these steps once a year, and you’ll be rewarded with a garden tool that ages a lot better than you do!

If all of this seems like too much hassle, you can always take your mower to be serviced professionally, but be aware that it can cost more than you would expect, and when you can do most of, if not all the work yourself, why bother paying someone else to do it?

About Terry Smith

I’m Terry Smith from, a professional landscape designer, hobbyist gardener, and barbecue fanatic with 20 years experience building and restoring. So as you go through my site you'll watch me document some of the professional garden installs I make as well as the major projects I take on at home. While sharing those experiences and guiding you, I'll be recommending some great tools I use to enable this along the way so you can really buy in confidence. Always feel free to pop me a message:

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