How to Rebuild a Non-Rebuildable Muffler, Spark Arrestor

Aug. 16, 2010 By Rick Sieman

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I recently picked up a decent 1990 Kawasaki KDX 200. This has always been one of my favorite bikes and I saw no reason why this one should become an exception to the rule. I got it for a great price and a short run down the street told me that the bike felt solid.

Here’s the stock KDX 200 muffler/spark arrestor.

Later on, I ran it on the dirt and found that there was a flat spot in the power band from about 4500 RPM on up. I checked the jetting and it was okay, and the sparkplug was more or less in the ballpark. After checking all the usual suspect areas, such as the air filter and worn-out reed valves, I turned my attention to the muffler.

And there was the problem. My first clue was a whole bunch of black mung and drool coming out the end of the muffler. I inserted a wooden rod down into the muffler and rotated it around a few times. It came out coated with black grunge.

A quick look at the tip revealed a whole lot of crud coming out of the muffler.

The muffler itself was of the non-rebuildable type, meaning that it was put together with pop rivets and not designed to come apart for cleaning or packing replacement. This didn't slow me down a bit. With the aid of a handy drill, I was able to make rather short work of the aluminum rivets. Once the rivets were apart, I was able to lightly tap on the muffler with a rubber hammer and take it completely apart.

A properly sized drill bit is one that's just exactly the same size as the aluminum rivets holding the muffler together.

While most of the muffler came apart OK, the spark arrestor insert itself was very stubborn to remove. By using a long extension and a hammer, I was able to gently tap on the insert and eventually to free up. When I removed it, the reason for the hesitation in the power became more than apparent. The spark arrestor insert was completely clogged up, and it's amazing that the bike was able to run at all.

When the rivet is drilled through, a large flat piece is left over.

When I decided to rebuild this muffler, I didn't really need the spark arrestor insert here in Arizona. To set a fire in the desert, you'd have to be some sort of miracle worker and I figured that simply rebuilding and re-packing the muffler would be the answer. So follow along as we go through the process.

The tip of the muffler can now be gently pried apart with the aid of small flat screwdriver.

Here's the tip off the muffler assembly.

The internals of the muffler can now be gently pulled out of the body.

Here are the guts of the assembly. As you can see, the packing is loaded with an oily residue.

To get the spark arrestor out, it is necessary to use an extension and a hammer.

Spark arrestor that was removed.

This shows the relationship of the spark arrestor insert compared to the muffler itself.

We enlisted the aid of Stephen Gautreau and found a core from an old muffler about the same size as the stock core. Steven runs SG Cycles in Mesa, Arizona

The core from an old Husky muffler was the same size as the KDX 200.

A bit of tack welding assured that the new core wouldn’t slip around.

If we wanted to reuse the old spark arrestor insert, it would have been necessary to soak it in a solvent for many days, or you needed to burn it with a propane torch to get the accumulated crud off of the part.

Instead of spending a whole lot of money on special repacking kits, we stopped by Ace Hardware and picked up a fiberglass insulation kit for under four bucks.