Common Petrol Lawn Mower Problems

Repairing a petrol lawn mower

Are you having issues with your lawn mower? If you’re stuck Googling “Why does my petrol lawn mower keep cutting out?” you’re not alone. So the good news is that we’ve got loads of help for you. The bad news, though, is that there are a lot of potential answers. Let’s just dive in, as this is gonna be a hefty article.

So what’s on the docket today?

Today’s Topics Include:

That was a mouthful! Luckily, though, a number of these are pretty quick and easy fixes, so let’s get going – there’s no time to waste.

Petrol Lawn Mower Problems & Fixes

Repairing a petrol lawn mower

Now, some of these questions and solutions are more complicated than others, so I’ll try to go in order of complexity. If you have a specific issue, though, chances are that we’ve got the answer here, so feel free to skip on down if needed.

Now – let’s get going, shall we?

Why Does My Petrol Lawn Mower Keep Cutting Out?

Let’s start with the basics – why does your petrol lawn mower keep cutting out? There are a number of factors that can cause a mower to cut out, but the following are the most common:

  • The cylinder head gasket is failing (uncommon)
    • Only replacing the head gasket will solve this.
  • Clogged exhaust (common)
    • Solve this by cleaning out your mower’s exhaust; usually, clippings get stuck and jam things up.
  • Engine kill switch (uncommon)
    • Occasionally, the safety kill switch will begin to fail. Replacing the switch will solve this.
  • Fuel line & filter (common)
    • Regularly (twice per year) cleaning your fuel line and filter is vital to the long-term health of your mower. Check out the linked article below for a guide.
  • Oil (common)
    • Ensure you have the proper oil in your engine and that it’s been replaced recently. Old oil will cause loads of issues. Once again, check the linked article below for more information.
  • Carburettor (semi-common)
    • Clean your carburettor regularly, or risk your mower failing. It’s worth noting that the carburettor and air filter (next issue) should be inspected and cleaned together, as they function as a unit. Check out this video for visual guidance.
  • Air filter (common)
  • Spark plug (semi-common)
    • These are a dime a dozen and fail quite regularly. It’s good practice to keep a few spares on hand for when they inevitably fail and need to be replaced.
  • Fuel (semi-common)
    • Petrol generally lasts a matter of months, rather than years. If you haven’t replaced your fuel since last year (or longer), replace the fuel and clean your mower’s tank thoroughly.
    • Flush the tank with new fuel and then dispose of it before filling your tank with more fuel.
  • Mower bag (extremely common)
    • A full mower bag will shut off most mowers. If it’s full, empty it and you’ll be all set.

Check out our petrol lawn mower maintenance 101 article for help and advice with these issues.

Petrol Lawn Mower Cuts Out When Hot

Repairing a petrol lawn mower

There are six potential causes for a petrol lawn mower that cuts out when hot:

  1. Clogged air filter
    1. As mentioned above, the air filter affects how the carburettor (and mower) functions. Regularly clean and replace your air filters!
  2. Fuel filter
    1. Similarly, your fuel filter needs to be regularly cleaned and replaced. If not, the refuse in your fuel will get in the carburettor – and that’s no good. Replace old filters and clean new (metallic) filters.
  3. Spark plugs
    1. As discussed above, the spark plug affects how your mower starts and performs. Keep a few extras on hand and replace your spark plugs regularly.
  4. Overheating
    1. Engines in lawn mowers can absolutely overheat. If you’re mowing on an exceptionally hot day (or for an extended time), simply move the mower out of the sun and take a break. It’ll recover in time.
    2. Top off your oil.
    3. Inspect the engine’s cooling fins for dirt or damage, replacing and cleaning them as needed (after cooling the engine).
  5. Lubrication
    1. Again, regularly check and top off/change your oil. Change it at least once, if not twice, per year.
  6. Compression
    1. Replace worn pistons
    2. Tighten loose bolts near the engine’s cylinder head
    3. Replace broken valve filters and push rods
    4. Inspect your crankshaft for damaged/worn valves and gaskets.

Why Does My Lawn Mower Only Run For a Few Seconds and Then Die?

This is a commonly-asked question that essentially boils down to the same answers as in our “Why Does My Petrol Lawn Mower Keep Cutting Out?” section. Take a peek up there, and replace parts as needed, cleaning those that are dirty.

Why Does My Lawn Mower Run For a Few Minutes and Then Stop?

Repairing a petrol lawn mower

As mentioned above, the most common causes of a lawn mower cutting out after several minutes are:

  • Faulty or dirty spark plugs
    • To fix this, clean and replace the spark plugs as needed.
  • Faulty ignition coil
    • To fix this, inspect and replace the coil as needed.
  • Blocked or dirty fuel delivery line
    • Flush your fuel line with fresh fuel, filter and dispose of the first batch of fuel, and then refill your fuel tank and test the motor.
  • Blocked or dirty air intake/filter
    • Inspect your air filter and intake port, clean out refuse if needed, and replace the filter if it’s gnarly.
  • Faulty fuel cap
    • This is the cap that sits on your fuel tank inside the engine. If it get heated up and warps or breaks, it’ll allow air into your fuel, causing the engine to shut off. Replace the cap and this will (theoretically) solve the issue.

How Do You Fix a Lawn Mower That Starts and Then Dies?

You’ll likely need to clean and replace one of the parts that have been listed several times in this article thus far – your spark plug or ignition coil, fuel line, air filter and carburettor, or fuel cap. Work in that order, as each bit gets increasingly difficult to clean and somewhat more expensive.

Why Does My Petrol Lawn Mower Rev Up and Down?

I’ve got a surprise for you – that’s right, it’s the same dang parts causing all sorts of issues! If your petrol lawn mower begins revving up and down, there are a handful of likely culprits that we’ve discussed ad nauseam by now:

  • Air filter & carburettor
  • Spark plugs
  • Old or contaminated fuel,
  • Dirty fuel line

How to Fix a Petrol Lawn Mower That Revs Up and Down

Repairing a petrol lawn mower

Take a peek at our “Petrol Lawn Mower Maintenance 101″ article for details on how to clean, locate, and replace your air filter and carburettor. For the other parts, keep reading:

Spark Plug

This is located (more often than not) directly next to your air filter and carburettor. Simply pull it out and pop in a new one, or scrub any rust or dirt off of the old one if you’re keeping it. Using steel wool is a good, quick fix here.

Fuel & Fuel Line

You’ll need to either replace the fuel in your tank and flush the tank to remove gross stuff or replace the fuel line altogether. If you need to replace the line, it’s likely better to buy a new mower, as it can be both rough to do and requires precision that most DIYers simply don’t have.

To flush your tank, do the following:

  • Drain all fuel out of your tank.
  • Run a full tank of petrol through your tank, draining and filtering it once done. This removes any buildup from the tank.
    • Repeat this process using the filtered fuel, running it through your fuel line to remove any buildup or gunk.
  • Once finished, refill your tank and test the motor. If it still encounters issues, it’s likely you’ll need to check your fuel line for damage.

Why Won’t My Petrol Lawn Mower Start?

The same culprits are popping up their ugly heads once again. If your petrol lawn mower won’t start at all, here’s what to check:

  • Spark plugs & ignition coil
    • These are what actually start the motor and ignite the fuel. If they fail, the engine won’t start, period.
  • Air filter
  • Fuel filter

Let’s talk fixes now, yeah?

How Do You Fix a Petrol Lawn Mower That Won’t Start?

Repairing a petrol lawn mower

The spark plugs are easily replaced if needed, though often, all they need is a quick clean. Give them a scrub, remove any buildup or gunk, and pop them back in, ensuring they’re as tight as possible.

The air filter will likely need to be cleaned and/or replaced, as detailed in the linked article above. As for the fuel filter, here’s how to replace it:

  1. Set your lawnmower on a flat (non-sloped) surface.
  2. Remove the fuel pump fuse, directly next to the fuel pump.
  3. Disconnect the battery (if you have one) terminals
  4. Disconnect the fuel lines
  5. Remove the filter – it’s usually held in place with small plastic clips.
  6. Replace the filter (they’re extremely cheap and cleaning them gives diminishing returns in quality)

Why Will My Lawn Mower Turn Over But Not Start?

The most common causes of a lawn mower turning over but not starting are a faulty or dirty spark plug(s), dirty or faulty air/fuel filters, dirty or failing carburettor and fuel line, or dirty fuel tank.

Each of these fixes has been detailed above.

Why Is My Petrol Lawn Mower Smoking?

Petrol lawn mower smoking

This depends on the colour of smoke coming from your lawn mower.

White smoke is generally caused by oil that’s hit the engine and started to burn. This is not only easy to have happen, but generally harmless in the moment. Let it sit, stop smoking, and once cooled, inspect the motor to find any bits of oil that may have spilt. Give it a wipe and scrub, and you’re set!

Black smoke, on the other hand, is a sign that the fuel and air mixture in your engine has become too rich. This means that air isn’t making its way into the fuel as efficiently as needed. Think of when you try to start a fire and accidentally pack the kindling too tightly – it’s the same thing.

Blue or white smoke in excess is a sign that the combustion chamber’s seals have failed. This is a very serious problem – read below to see how to fix it.

Do not ignore black smoke, as it is a sign of a larger issue that will reoccur until addressed. Skip down to the sections below for fixes.

Why is My Petrol Lawn Mower Blowing Out White Smoke?

As mentioned above, your petrol lawn mower blowing out white smoke is a sign that oil has begun to ignite on your engine. This is entirely normal and will resolve itself – though cleaning it up won’t hurt, either.

How Do I Fix White Smoke From My Lawn Mower?

To fix white smoke coming from your lawn mower, clean the engine! It’s likely that oil has made its way somewhere hot and begun to ignite. Simply take a dry rag and soak it up, and the problem will solve itself.

Just be sure not to do this while the engine is hot still – that hurts.

How Do I Stop My Lawn Mower From Smoking?

If it’s just a little bit of white smoke, look above. If it’s black smoke, do the following:

  1. Clean your air filter, replacing it if needed.
  2. Inspect the carburettor
    1. Generally, black smoke will be caused by your carburettor being loose. Simply tighten it up (usually housed with screws) and the problem should be solved.

If, however, you’ve got a lot of blue or white smoke, I’ve some bad news for you. This is a sign that your head gasket, combustion chamber seal, or breathing tube has failed (usually in a catastrophic manner).

If you see lots of blue or white smoke from your lawn mower, it’s likely that your mower is dead. If you know a good mechanic, bring it to them – otherwise, it’s time to start shopping for a new one.

Why is My Petrol Lawn Mower Chugging?

If your lawn mower is chugging, it’s likely that the engine isn’t getting enough air. Unsurprisingly, my advice hasn’t changed in this area – change or clean your air filter and the problem should resolve itself.

How Do I Stop My Lawn Mower From Sputtering?

The most common cause of a sputtering lawn mower engine is that water has made its way into your fuel. The only guaranteed fix for this is to completely drain all fuel from your tank and dispose of it, and then replace it with fresh fuel. I recommend leaving the mower in the sun for a bit to allow any excess moisture to evaporate before adding the new fuel.

This will ensure you don’t have to waste fuel by constantly draining it.

Why is My Lawn Mower Not Running Smoothly?

Unlike most issues here, if the mower starts but struggles to maintain power, it’s a sign that your spark plugs and ignition coil are actually functioning properly. This means that you have an issue elsewhere – usually the air intake or fuel system.

Check your filters (both fuel and air), clean or replace them as needed, inspect your fuel line and tank for buildup and gunk, and clean them if needed. Additionally, check the air intake vent on your fuel delivery system for bits of grass or dirt that have lodged themselves in and ensure you have new petrol, rather than fuel from 2+years ago.

How Do I Stop My Lawn Mower From Surging?

Surprise! It’s the same three culprits – your air filter, fuel system (including the vent, filter, and fuel itself), and carburettor.

You’ll need to clean each as needed and inspect them for damage, as detailed in just about every section above.

Can a Dirty Air Filter Cause a Lawn Mower Not to Start?

If you’ve been reading along, you already know this answer. If not, why? I wrote this just for you!

Writer’s anger aside, the answer is as mentioned numerous times above.

Yes, a dirty air filter can cause a lawn mower not to start. It will prevent air from making it to the fuel system, preventing it from getting the oxygen needed to ignite. Clean your air filter thoroughly and replace it if needed and the problem will resolve itself.

Conclusion

All in all, while lawn mowers are surprisingly complicated machines for such a simple task, the culprits of all your issues generally boil down to one of a few small parts. The filters (both fuel and air), fuel delivery system, petrol you use, spark plugs and ignition coil, and carburettor are going to be the cause of 9 out of 10 issues you experience.

It’s worth noting that a majority of these issues can be resolved prematurely with regular maintenance. So every season you start to mow, give your mower a bit of love and check out the common bits that fail – you’ll thank me, I promise.