The SR500 sidecar - what goes in must come out

 So far the SR500 sidecar has fared exceptionally well in the context it was designed for. It is a reliable starter (when cold), it is pretty fuel efficient for a sidecar as it is using about the same amount fuel as the TR1 and it's not very noisy. What sounds pretty good (pun intended), has got a bit of a downside though: The performance initially was somewhat lackluster and even though the original exhaust was indeed on the quiet side, it made some weird chirping noises and judging by how much better the old girl ran without a plug in the AFR-bung and thus reducing back-pressure a plan was hatched.

In order to take off the exhaust, I originall envisioned two M8-bolts going into the muffler bracket. Which wasn't exactly an astounding feat of modern engineering creativity, but solved the mechanical problem of mounting the exhaust to the hanger sufficiently sturdy. There were two problems with that though: The bolts tended to come loose and because both of them were very hard to reach, tightening them was a major p.i.t.a. and don't even get me started on sneaking in lock washers. 

The solution was simple and almost elegant. With the rear bolt replaced with a stud it was much easier to align the exhaust and bracket and as the rear was easily accessible with a wrench (and almost impossible to reach with an allen key) this totally made sense. At the same go a 12mm bracket was added to stop the exhaust hitting the swingarm when the bike was propped up on the center stand. (Admittedly not something that happens very often, but it left a nasty scratch in the swingarm's paint and a use case that comes up on Winter rallies when putting on chains.)

In the picture below, you see the last photo of the regular M8 nut, before it went on its merry way on the way home from the workshop, never to be seen again. It was subsequently replaced with a nyloc nut.

But there's still a wee little elephant in the room, right? How do you loose the plug of an AFR-bung? Well, funny you should ask... imagine the following situation: You ran that little sidecar all day with a wideband AFR-probe all day, then it quickly became dark (as it does in Winter) and because the exhaust was still hot, you just screw in the plug lightly, so it would come up to temp and not seize in the threads. As you have have to wait anyway, you go in wash your hands and promptly forget about the whole thing. You do about three or four kilometres and suddenly you have big blue streaks of flame coming out of the aiming right at your knee. 

Also a TM36 with a working mix screw is a really sensitive carb, just the slightest tweak results in the carb jumping around between 12.3:1 and 11.8:1!

After browsing the website of my exhaust-components supplier, I found out that they also offered the same muffler with a resonance chamber in the middle and were also willing, for what I can only call a very reasonable price, to make them as long as I want. So for reference this was the old setup:

... and it emitted somewhere between 78.3 decibels (cold) and 77.5 decibels (hot).

Now the new muffler is approx. 10cm longer than the old one with a 10cm long resonance or expansion chamber in the middle, meaning that the amount of actually packed volume stays the same, but I essentially have two short mufflers in one enclosure.

First time use of a widebody gas lense and whilst HEAVY on the Argon, the results speak for themselves.

Interestingly enough, the muffler does a tremendous job in quieting down the bike. Now I hear you say that's an exta 6 decibels at idle, how is that even remotely related to a more quiet bike? As a matter of fact this was recorded without ANY muffler insert in the tip, so a substantial decrease in the noise levels is possible and for legal reasons, I only have to shave off 0.8 decibels to pass. Also as it's a very low, bassy noise it's a lot less obtrusive than before.

And that's what the longer muffler looks like on the bike, it doesn't stick out the back and pretty much makes maximum use of the space available without looking goofy.

So what lies ahead: make a muffler insert, to get back down to somewhere around 81 decibels, fit a one-size smaller pilot jet. Starts fine when cold and almost instantly has an idle, but bit heavier on the fuel consumption and starting it when hot is only possible by slightly lifting the slide.