Aprilia RS 125 - decatting and exhaust appendix

[DEADmetal]

This exhaust is taken from a stock factory FP 2006 RS 125 new shape. I'll be cutting out the cat and recirculation pipe, so i need to know what's this appendix for. If it's a restrictor, i'll cut it out as well.

https://i.imgur.com/vSCzTO3.jpg

[stevo as b4]

It's a resonator tube like those fitted to scooter exhausts. It needs to be removed and plated over. As it is, it's adding volume to the exhaust and changing the resonant frequency of the pressure waves. It can make the pipe work better at much lower Revs, but it won't make any power where the engine is designed to work properly.

Will be interesting if you dyno this bike once you've removed all the restrictions and jetted it correctly, just to see if you can get closer to early RS125 extrema bhp figures, or if there's other changes made to the exhaust, engine, carb or ignition to de-tune these later bikes and improve their emissions.

Daft idea it was trying to build a clean running two stroke. It goes against every working principal of them, and they are supposed to pollute the planet like a mother fucker.

[DEADmetal]

[DEADmetal]

By the way, do I need to rejet it after decatting it (emptied the expansion chamber completely)? The bike is otherwise stock (and fullpower), with stock jetting.

I wasn't actually worried about it, because i've heard that the stock jetting is rich and besides my exhaust can tip was getting oiled up a bit. However, it's better to be sure than sorry.

[Riejufixing]