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Yoshimura Exhaust Pipe Mod

I purchased my 1997 TLS1000S used. The previous owner kept in great condition. One of the few changes he made was the addition of black Yoshimura RS3 mufflers. When I questioned the original owner why he chose those pipes he said 'Just wait till you hear it'. He was right. That big V-twin sound is wonderful. But these cans might have given us too much of a good thing. Maybe I'm just old, but I thought it might be time to reduce the volume down from '11'.

My first attempt at quieting the bike was frustrating and unsuccessful. I was only able to get one of the two cans apart and repacking alone made only a small reduction in noise.

One positive aspect of my first attempt was the development of a tool to disassemble the cans. I learned that the front and rear machined aluminum caps on these Yoshimura RS3 pipes do not easily come out of the muffler cans. With no real way to get ahold of the caps or can, I realized I would need to think outside the box. The front cap has four threaded holes for the bolts that hold the can to the header. I took the weight off my slide hammer, slid it over a long bolt, and threaded the bolt into one of the threaded holes in the front cap.

During my most recent disassembly attempt I was able to use this makeshift slide hammer to break loose and remove the front end caps. Once the front end caps were off I could pull the perforated cores. Only after removing them did I noticed that they were slightly tapered. Wider at the inlet. narrower at the exit. These cores, just like I expected in a race bred pipe, were pretty much straight through. Which explains why these pipes were too loud. To my surprise I also noticed that these cores were double walled. The cores are made of two perforated tubes arranged with one inside the other. I've included a hand drawn schematic of the inner design of the muffler at the end of this article. This drawing helps show how the washer pushes some of the exhaust gasses though the inner perforated core.

I had seen a picture of a restricted perforated core. I wasn't sure where to get one but decided I could modify what I had to accomplish the same thing. I decided to try using washers as restrictors. The goal was to get some, but not all, of the exhaust (and sound) to travel through the mesh of the inner core, into the void between the two perforated tubes where there was no washer in its way, and back through the mesh into the inner core. I don't think I would have tried this if the Yoshimura exchaust pipe core wasn't double walled.

A wooden dowel was used to push a single washer from the inlet end into the tapered inner core of each can. The washers are just pressed in place just in case I change my mind. I repacked the mufflers with fiberglass cloth and then reassembled both pipes.

As soon as I fired up the bike it was obvious the modification made a sizable difference. The deep V-twin sound still remained but at a more moderate volume level. It wasn't until after my first test ride that I was able to accurately summarize the change the tonal change. My washer muffler modification had 'removed the bark but not the boom'.

Schematic showing use of washer as exhaust diverter inside Yoshimura muffler.