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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.

ATV spark arrester

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 rev at a much higher rpm and the gas oil mix tends to soot up and gather inside the muffler. As the tailpipe gets hotter, the soot catches fire, and if not for the spark arresting screen inside the exhaust tailpipe, the embers may be blown out of the tailpipe possibly causing a forest fire.

The USDA spark arrester guide specifies that all internal combustion machinery must comply with forest services spec 5100-1d – they must have a working spark arrestor. While USDA states you need a spark arrester to ride on public trails, it is permissible to operate an internal combustion engine without a spark arrester on private lands.

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.

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.

But if you don’t see a stamp, you can just check for an arrester yourself, the spark screen is easy to spot. Use your phone light to look into the tailpipe, if you see a mesh screen, you have an arrester 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 the intake of air or the exhausting of 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.

How Often Should I Clean Spark Arrester?

All engine manufacturers will have their own specified maintenance schedule for cleaning however every six months or about 150 hours of riding is normal for four-stroke engines. Two-stroke spark arresters will require more regular checking and cleaning.

Diagnosing a Blocked Spark Arrester

Stroke 4

Spark arresters as you know, block or catch embers but they also trap carbon deposits in the very fine screen mesh which if not removed chokes the engine preventing spent gases from leaving the motor.

If spent gases can’t leave the muffler quickly it follows, the new engine cycle can’t begin, which results in poor engine performance. A fast efficient bike needs a clear airway and a clear exhaust path.

Two-strokes suffer the most, the oily gas mix of a two-stroke causes the arrestors to clog up more quickly. The arrestors block up with soot and begins to choke the engine progressively.

Symptoms of a blocked arrester vary by how badly blocked it is, typically you’ll notice:

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

How to check the arrester?

If it’s been six months since you last cleaned it, and or you’ve covered about 150 hours riding then you can be sure it needs cleaning.

  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 or the screen is worn out. Old screens simply burn out in the center where they get hottest and see the most action.

How to Clean Spark Arrester

This is a really simple job that brings huge benefits to your engine. Removing and cleaning a clogged arrester is a five-minute task. You’ll need a Philips screwdriver (usually) and a wire brush.

The process is as follows:

  • Locate the fasteners on the silencer body and remove
  • Remove the arrester (metal screen)
  • Use a wire brush to remove sooty carbon deposits (should be able to see through the screen when clean)
  • Refit the arrester (add some copper grease to the arrester screws)

Replace a broken arrester, otherwise, it isn’t an arrester.

Job done!

You’ll find the tools I recommend here on the ATV tools page and you’ll find common spare parts here on the ATV parts page and on the Dirt bike parts page.

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