Skip to Content

Riding Lawn Mower Won’t Start After Running (How to Fix?)

Riding Lawn Mower Won’t Start After Running (How to Fix?)

If you have a large lawn to cut, owning a good sit-on mower is more than just a pleasant luxury, it’s a necessity. Beyond a certain size of lawn, it is no longer feasible to mow with a traditional push mower, but a sit-on version will let you finish the job in no time.

However, sit-on mowers – like other types of mower and just about any kind of power tool – can develop problems, and one is that it starts up fine at first but then won’t start up again after being used. Here, we will look at the question of what to do if a riding lawn mower won’t start after running.

The basic tenet of repair work

The basic tenet of repair work

Before we start, let’s just remind ourselves of the proper procedure to follow when trying to repair any kind of machinery.

If you want to repair something, first, you need to identify the problem. To do this, you need to narrow down the search area to determine where the problem lies. By systematically eliminating all possibilities, you can locate the problem – and once you find it, you can fix it.

First question

In order to work out where the problem lies, you need to ask yourself some questions. The first question – a very obvious one – is why the lawn mower stopped in the first place. Did you stop it, or did it stop by itself?

This is a very important question to ask since it will help you determine where to start looking for the problem. If the mower won’t restart after stopping by itself, the fact it was running might not be relevant.

By this, we mean the fact that it won’t start after running might be coincidental – that it was running before might not be related to why it won’t start now, and the problem might lie elsewhere.

To begin with, we will look at why your mower won’t start if you stopped it yourself – because in this case, the problem is probably to do with the fact that it is hot and not something else.

Why it won’t start after running if you stopped it yourself

Why it won’t start after running if you stopped it yourself

Problems with restarting a mower that has been shut off after running are almost always related to compression, i.e. the engine’s ability to build pressure on the cylinder.

Basically, when an engine runs, it heats up – and metals change size and shape when they are hot. The change is almost imperceptible, but even this tiny amount of difference can cause a problem.

Since the valve changes size, it may no longer be able to close 100% and so you won’t have the necessary pressure required to start the engine.

To see if this is the case, test the compression when cold and test the compression when hot. If you have more compression when cold, this is an indication that you have identified the problem. To rectify it, ensure that the valve lash is set correctly when cold.

The problem with this is that it is not an easy job either to test this or to fix it by yourself unless you know your way around engines. If you are not sure what you are doing, you might be better off asking a professional to check for you.

Another possibility is simply that the engine is overheating. This could happen if grass clippings clog the cooling fans. This is something that is easier to check, so you should eliminate this before calling in a mechanic.

Here’s a video of someone dealing with a similar problem.

What about if you lose power during mowing?

If your mower shuts off while you are mowing and won’t restart, you might suspect that it is a heat-related problem, but it could also be something else. Here are some other possibilities that you should try to eliminate.

· Are you out of fuel?

So we’re starting with the most obvious, but in the interests of being systematic, check it.

· Having problems restarting after running out of fuel and refilling?

Perhaps your mower stopped because it was out of fuel but after you refill it, it still won’t start. This is probably not a heat-related problem at all. Here, it is more likely that there was some debris floating in the fuel and was sucked into the fuel line when the fuel ran out.

To rectify this problem, ensure that the fuel lines are clean and free of debris. After removing any debris, it should start again.

· Cutting tall grass or build-up of grass under the mower

It is possible that the grass you are cutting is too long and is clogging up the mower, causing the engine to stop. Try clearing out the cuttings and then adjusting the cutting height.

Similarly, if the mower becomes too clogged up by grass cuttings, the same may occur. Try clearing it out and trying again.

· Old or dirty spark plugs

This is another obvious one to check. If your spark plugs are old or dirty, replace them. This will probably increase your mower’s performance instantly.

This is the kind of problem that might make you think the problem is because the mower has been running when actually the problem lies elsewhere. Make sure your spark plugs are in good condition, clean and properly connected to eliminate this possibility.

· Dirty air filter

As with the spark plugs, this is the kind of problem that can make you think the problem is heat-related when it isn’t. If your mower loses power and then won’t restart, it might be due to dirty air filters.

This is a simple problem to check and fix. Make sure the filters are clean and in good working order and try again. If this was the problem, it should start up again easily.

Eliminate all possibilities to find the problem

If you have a problem restarting your mower after it has been running, the first thing to do is to eliminate all the simple issues.

If none of the more obvious problems are to blame, you could well have a problem with compression due to a valve. If this is the case, unless you are very confident around engines, you might need to think about calling a professional.

Leave a comment

Your email address will not be published. Required fields are marked *