Do Four Strokes need Spark Arrestor? (Yes, here’s why)

Spark arrestors on some bikes can look pretty cool, but more importantly, they serve a very useful function.

All internal combustion engines operated in the USA must have spark arrestors fitted, including four-stroke engines.

In this post, you’ll learn what a spark arrestor does, where you must use it, and why some don’t like using them.

Spark Arrestor

Spark arrestors are needed on all internal combustion equipment, two strokes or four strokes. It is fair to say that two-strokes are more commonly associated with sparks from the tailpipe.

That’s because two strokes much higher rpm and the gas oil mix tend to soot up and gather inside the muffler. As the tailpipe gets hotter, the soot catches fire, and if not for the screen, it would be blown out of the tailpipe.

The USDA specifies that all internal combustion machinery must comply with forest services spec 5100-1d – have a working spark arrestor.

How to Check If You Have One?

The most kit will have one fitted from new but do check before you pull the pin. A good shop won’t have a problem fitting a spark arrestor. Modified used equipment likewise may not have them installed.

A spark arrestor or spark screen is easy to spot. They’ll all be fitted at the very tail of the exhaust. The arrestor is basically a mesh screen that catches the embers and prevents them from exiting the tailpipe.

Most quality makers will have the spark arrestor part number and flow rating marked for all to see. Take a look at the very tip of the exhaust, look for model number or patient or flow rate, something like 28 cfm. If not, use your phone light to look into the tailpipe. If you see a mesh screen, you have one fitted.

Can I Fit One?

Yes, you can fit a spark arrestor easily. The aftermarket suppliers will have one to suit your make and model. Most require a drill and screws or some pop rivets to secure them right onto the existing tailpipe.

Do They Effect Performance

Yes, they do. Anything that restricts either intake of air or exhausting gases will affect performance. But truthfully, it’s very slight, and most won’t even notice it.

What you will notice is a distinct lack of performance if you don’t maintain the spark arrestor. A two stroke will need more attention than a four-stroke engine. The oily gas mix of a two-stroke causes the arrestors to clog up more quickly.

The arrestors block up with soot and begin to choke the bike, symptoms vary by how badly blocked it is, typically:

  • Hard starting
  • Starts then dies
  • Lacks power
  • Erratic running
  • Won’t start

To diagnose a blocked arrestor :

  1. Check the exhaust out put, is the exhaust pressure weak or strong?
  2. Remove the screen, is it dirty?
  3. Run the engine, has that improved the issue?

The screens are reusable but replace them if they’re choked or damaged. Old screens simply burn out.

You may find the following posts helpful:

How often should I service my ATV?

Do ATVs have titles?

How often should I start my ATV?

How to start ATV in cold weather?

John Cunningham

John Cunningham is a certified mechanic and writer on I’ve been a mechanic for over twenty-five years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of ATV ownership, from maintenance & repair to troubleshooting.

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