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


Spark arrestor’s 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 2 stroke or 4 stroke. It is fair to say that 2 strokes are more commonly associated with sparks from the tail pipe.

That’s because 2 strokes much higher rpm and the gas oil mix tends to soot up and gather inside the muffler. As the tail pipe gets hotter the soot catches fire and if not for the screen, it would be blown out the tail pipe.

The USDA specify 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?

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 simply catches the embers and prevents them exiting the tail pipe.

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, just use your phone light to look into the tail pipe, if you see a mesh screen, you have one fitted.

Can I Fit One?

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

Do They Effect Performance

Yes they do, anything that restricts either intake air or exhausting gases will effect performance. But truthfully it’s very slightly and most won’t even notice it.

What you will notice a distinct lack in 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 easily.

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.

John Cunningham

John Cunningham is an certified mechanic and writer on ATVFixed.com. I’ve been a mechanic for over twenty 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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