Hello - I recently took possession of a 2021 R9T Classic, having sold my F800S, which had a glorious exhaust note (thanks to an aftermarket Akrapovic exhaust with its dB killer removed) and was not impressed with the Euro 5 compliant sound that my new bike produced. Yesterday, I followed the procedure you generously provided and, my word, what a difference! Bigger, fatter bass notes and even some popping during deceleration. I still prefer the exhaust note of the F800S, with its bubbling and glorious gurgling, but I prefer design features and the flat twin of R Nine T to my former bike. Again, thanks for sharing.EDIT : The following procedure is for a quick and dirty disconnection, or destined to someone who doesn't care about keeping the cables attached to the flapper assembly or just wants to try it out. If you'd prefer a cleaner mod, do familiarize yourself with this post first then check out this post by @LWIRWA. His take on it keeps the plastic housing on the pipe, as it's welded in place anyway, but gets rid of the cables.
I offered member @RninetDOG to provide a tiny how-to guide regarding the disconnection of flap cables, so I thought that doing it here might be best.
Here we go :
0) We'll need a 10mm flat spanner as well as a ratchet wrench with a Torx T25 bit. Some thread-locker might be advisable.
1) Locate the two screws on the flap's plastic housing. One is visible from the side-stand side of the bike, the other one will be easier to reach from the other side. It's basically facing the ground, laying down will help. Remove them.
View attachment 144565
2) Remove the plastic housing by sliding it towards you. You'll be greeted by this :
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On this picture one of the two little brass tabs is removed from its nest for illustration purposes. Use the 10mm spanner to unscrew the nuts which hold the cables to the metal housing. Pull the cables towards you. Push down on both of the brass tabs, they should dislocate easily and the cables spring straight out like this :
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From there on it's already time to reassemble everything. Push the cables back in position and tighten the 10mm nuts, leaving the tabs hanging somewhere in the middle of the "cup" of the flap, as it'll be easier to then reinstall the plastic housing.
The screws which hold the plastic housing should have some threadlock on their thread. As mine were extremely easy to screw out and back in, I didn't bother to clean the threads and just applied a tiny amount of medium strength threadlock and tightened by hand.
That's all !
I couldn't recommend trying this solution out highly enough before any slip-on purchase or further modification. Totally reversible in mere minutes, very effective at bringing back some much-missed exhaust sound (especially at low revs / small throttle openings), and completely free to boot. It might be just enough for you, as it was for me. Do try it !