The spark arrestor is a small mesh screen at the muffler outlet that is easy to forget until it clogs. Here is how to tell if yours is choking the engine, and how to clean or replace it.
The 30-second answer: If a generator has lost power, runs hot, or leaves heavy black soot at the exhaust, a clogged generator spark arrestor may be choking it. Let the muffler cool, remove the screen from the muffler outlet, scrub off the carbon with a wire brush, and replace it if it’s torn. The part costs $8 to $15 and takes about 15 minutes.
The short version
- The spark arrestor is a small screen in the muffler outlet that stops hot carbon particles from leaving the exhaust.
- When it clogs, exhaust can’t escape, so the engine loses power and heats up.
- Let the muffler cool completely before touching it. Muffler metal stays hot long after shutdown.
- Many national forests and wildland areas require a working spark arrestor, so a missing one can be a legal problem when camping.
What Does a Generator Spark Arrestor Do?
Every small engine throws out tiny bits of burning carbon with the exhaust. In dry grass and brush, one of those glowing specks can start a wildfire. The spark arrestor is a fine wire mesh or a perforated cup built into the muffler outlet that catches those particles while letting exhaust gas pass. That’s the job, and it does it well, but the screen does get dirty. Over time the carbon it catches packs into the mesh and restricts flow. An engine that can’t breathe out can’t breathe in, so it loses power, runs hotter, and sometimes smokes or backfires. A packed screen is a common hidden cause of “no power under load.” It’s a five-dollar fix that people overlook because nobody thinks about the exhaust end.
Symptoms of a Clogged Spark Arrestor
- The generator bogs down under load that it used to handle (generator bogs down under load)
- The engine and muffler run hotter than normal (generator overheating)
- Black, oily soot builds up around the exhaust tip
- Exhaust sounds raspy or restricted, or the engine is harder to start
- The muffler glows or smells like hot metal and carbon
A rich-running engine, an overfilled oil level, or lots of choke use all feed carbon into the screen faster. If it clogs again quickly after cleaning, look at the cause too.
Where Is the Spark Arrestor?
On most portable generators, the screen sits right at the end of the muffler where exhaust exits. It’s held by one or two screws, a clamp, or a small plate. Some mufflers have it built in, and you can’t remove it without taking the muffler off. On a few budget models, there isn’t one at all. Look at the muffler outlet. If you see a small screw head or a metal ring around the tip, that’s the arrestor. Check your manual’s parts diagram if you’re unsure.
How to Clean a Generator Spark Arrestor
Safety — quick reminders.
A muffler can cause serious burns long after the engine stops. Wait at least 30 to 45 minutes after shutdown, and touch it lightly with the back of your hand before you work. Wear gloves.
You’ll need a screwdriver or a small socket, a wire brush, carburetor cleaner or brake cleaner, a rag, and safety glasses. It’s a 15-minute job.
- Shut the generator off and let the muffler cool completely.
- Remove the screw or clamp that holds the arrestor, and slide the screen out.
- Look at it. A clean screen lets you see light through the mesh. A clogged one looks solid black.
- Tap it to knock out loose carbon, then scrub both sides with a stiff wire brush. Spray carburetor or brake cleaner to dissolve oily soot.
- Check the mesh for holes, tears, or collapsed areas. Damaged screens won’t stop sparks, so replace them.
- Refit the screen with its hardware, and make sure it sits tight and doesn’t rattle.
Some folks hit the screen with a propane torch to burn the carbon off. It works, but it can weaken or warp thin mesh, and I’d rather scrub and replace. Years of working around aircraft taught me not to take shortcuts with heat.
Check the Muffler Too
While you’ve got it open, shine a light into the muffler outlet. If the inside is caked with carbon or oily residue, the muffler may be restricted past the screen. A badly clogged muffler can be soaked in cleaner or replaced. Replacement mufflers run $25 to $70 for most portables, and fit varies by model. If you find wet, oily carbon rather than dry black soot, oil may be burning in the cylinder, so check the level (overfilled with oil) and read generator exhaust smoke color guide.
Is a Spark Arrestor Required by Law?
In many places, yes. Federal rules for national forests and other wildland areas generally require internal combustion engines to have a qualified spark arrestor, and many states and local jurisdictions have similar rules in dry seasons. I live in Arizona, where fire restrictions come around every summer, and I always check the local rules before I take a generator camping. The requirements change, and they vary by agency and by year, so check the land manager’s current rules before you go. A generator with a missing or damaged screen could get you a citation, and far worse if it starts a fire.
Parts and Cost
| Item | Typical cost | DIY time |
|---|---|---|
| Cleaning supplies | $0 to $8 | 15 minutes |
| Replacement spark arrestor screen | $8 to $15 | 10 minutes |
| Replacement muffler | $25 to $70 | 30 to 45 minutes |
| Shop service | $50 to $120 | Drop-off |
How Often to Clean It
I check it once a year or about every 50 to 100 hours, and any time the generator feels weak. If you run it hard, use choke often, or burn a little oil, check it more often. It belongs on the maintenance list next to the air filter and the plug. My generator maintenance schedule has the complete rundown.
If the screen is clean and the engine is still weak, move on to generator runs rough and check the carburetor.
Video walkthrough
Frequently Asked Questions
Can I run a generator without the spark arrestor?
You can, but I won’t, and in many places it’s not legal around dry vegetation. Without it, hot carbon can fly out of the exhaust. I leave mine installed and clean it.
Can a clogged arrestor damage the engine?
It can contribute to overheating and valve damage if it’s ignored for long. I’ve seen exhaust valves burn from sustained restricted flow.
Does every generator have one?
No. Some don’t, and some have it built into the muffler. If yours doesn’t, you can add a clamp-on arrestor for $10 to $20 in many cases, as long as it fits the outlet.
Why is there oil on my arrestor?
Oil in the exhaust means oil is getting into the combustion chamber. I’d check the oil level first, then the air filter and breather.
How do I know if the screen is damaged?
Look for holes, torn or burned mesh, or a screen that has collapsed inward. If I can poke a pin through it, I replace it.