The muffler is one part of a gas mower that no one really pays attention to or appreciates until something goes wrong with it. You see, a muffler’s primary job is to reduce the amount of sound that your lawn mower produces. Whenever anyone asks “how can I make my lawn mower run quieter?” the #1 suggestion I would give is to check whether the muffler is damaged. If it is, replace it. If not, can you upgrade the current one to a better one? The muffler also has a second (and very important) role, which is to prevent exhaust sparks that could potentially ignite any dry debris that has made its way into the engine.
Some of the most common signs that a lawn mower muffler is clogged are a sudden increase in the amount of sound your mower produces, leaking exhaust fumes, a sputtering engine, and increased fuel usage.
Symptoms of a Clogged Lawn Mower Muffler
Before I get to explaining what you should do if your mower’s muffler is clogged or damaged, you first need to determine that it is in fact clogged or damaged. Here are the main signs to look out for.
Sudden Increase in Noise Output
As mentioned, the muffler’s primary role is to filter out a lot of the noise that is produced on each exhaust stroke of the engine. The hot gasses that are pushed out of the cylinder on this stroke can make quite a racket.
If you’ve been out mowing recently and suddenly noticed that the sound your mower was making jumped by a few levels, there’s a very good chance that the muffler could be clogged or otherwise damaged. This is not that uncommon after 2-3 seasons of regular use.
Engine Sputters and Stalls
The exhaust fumes are pushed out of your mower via the muffler. If the muffler is clogged, these fumes are not removed as effectively, and if they build up as the mower is running, it can make life very difficult for your engine. It’s not uncommon to see it running a lot rougher than normal and it may even stall.
This kind of symptom could also indicate a problem with your carburetor being dirty/blocked too, so if you clean the muffler out and still see this issue, that’d be the next thing to check.
Mower Using More Fuel
Honestly, the increase in sound is the main thing to watch out for, as it’s something you will notice instantly. But another symptom of a clogged muffler that you’ll see over a longer period is that your mower starts to use more and more fuel to do the same amount of work.
This is because with the build-up of exhaust fumes, the engine is forced to work harder and harder, and that requires more fuel. So fixing a clogged lawn mower muffler is not only good for your hearing and the health of your mower, it’ll save you money on fuel costs too.
How to Fix a Clogged Lawn Mower Muffler
You definitely don’t want to continue to run your mower with a clogged muffler, as things will likely go from bad to worse. Running your mower without a muffler is also not an option (without it, exhaust sparks are possible….). That means you’re left with just two options; you clean the muffler or you replace it.
Cleaning a Lawn Mower Muffler
You need to take all of the usual safety precautions before you attempt to inspect and clean your muffler. Let the engine cool down completely and disconnect the spark plug before you do anything else.
Next, you want to remove the muffler from your mower. What this entails will depend on the mower you have, as mufflers can vary quite a bit. On my mower, there are two bolts that have to be removed and then it can be detached.
When a lawn mower muffler becomes clogged, it’s usually the spark arrestor that is coated in soot that has built up through normal use. That part needs to be cleaned or replaced, and to do so you’ll need to disassemble the muffler to get at it. Once you’ve removed the spark arrestor, you can either clean it with a solvent (make sure you submerge it and fully soak it) or take a propane torch, heat it up and you’ll be able to simply knock the soot off afterward.
I have to say that this is not the most straightforward mower maintenance job, and if you’re not confident in what you’re doing, you might want to take it to a pro to handle instead.
Replacing a Lawn Mower Muffler
Once you’ve detached the muffler as per the instructions above, it’s worth taking a minute or two to inspect it to see if it’s actually worth cleaning, or whether a replacement would be a better option.
First thing first. Shake the muffler and see if you hear anything rattling around. If you do hear something, it’s likely that this is an internal baffle that has broken off and is now blocking the muffler’s airways. This needs to be removed. Sometimes it can be removed using a set of pliers, carefully and patiently extracting it through either the inlet or the outlet. If this is not possible, the only option might be to cut the muffler along the seam, remove the loose baffle and then weld the muffler shut again.
As well as the “rattle test”, watch out for signs of the following things in the outer casing of the muffler:
If you spot one or more of these things, and it looks as though your muffler has seen better days, it may be a better idea to retire it and source a new one. Just make sure it’s compatible with your mower and install it carefully. The difference will be immediately noticeable once you fire up your mower.
I just bought a used 2015 42-in cut yard machine with a power more 420cc motor and it runs good but is loud as hell should I replace the muffler and how hard is it to do
Hi Butch! I can’t find a lot of specific information about that model online but given the style of mower it is, you shouldn’t have too much trouble getting to the muffler to inspect it. Is there any obvious outside damage? As mentioned in the article above, any cracks or rusted-out sections usually indicate that the muffler needs to be replaced.
If the outside appears fine, the next step would be to disconnect the muffler so you can inspect it thoroughly. Taking a moment to give it a cursory clean, using the steps mentioned above, can help highlight any “hidden” damage. If there are any “loose” or “rattling” sounds, that’s an additional red flag.
If you do decide to go ahead and replace the muffler, replacing it shouldn’t take more effort than getting the original muffler off of your mower. In many cases, there are a few parts that slot together and two or four bolts holding everything in place. In rare cases, there may be a weld, especially if the muffler had been repaired or modified in the past.
My mower, for example, only has two bolts. Replacing the muffler, even on a slow day, will only take 30 to 40 minutes. If you do intend to DIY this task, always make sure to disconnect the battery before you start work and ensure that your mower is completely cool and on a solid surface. I hope this helps!
A neighbor gave me a used mower, a Honda push mower 5.5 engine, that he said runs well. But he tried to remove the muffler for some reason and sheared the bolts off. So it was free to me to fix. Project has not gone according to plan and likely won’t accept new bolts now. But, mower does run, and there’s a muffler shield box that covers the muffler. Is there an alternative I could place in that shield box that could act like a muffler that would be safe? Any ideas? Thanks.
There isn’t much you can do with the shield box, as this will likely disrupt the exhaust flow from the cylinder head and potentially cause issues. The best option would be to use a bolt extractor tool (around $10 from Amazon). This tool will get the old bolt out that has a broken head. Then if the threads are damaged and the hole won’t take a new bolt, you can use a tap and die set (around $20 from Amazon). A tap-and-die set will recut the threads. I’ve used this method a few times on older equipment, and it works perfectly.
Best of Luck!