Wow, I ain't never seen anything like that SLR. According to the blurb on it, it's a Scavenging Losses Rejection (SLR). (I think something may have been lost in the English translation)
It looks to be a simple backpressure device that bleeds down. Conceptually it is suppose to add backpressure to the cylinder just before the exhaust port closes, thereby reducing the amount of fresh mixture that can escape out the exhaust port.
However, as the RPM increases, so does the backpressure in the SLR. If anything, you would want the opposite, a backpressure device that gives more backpressure at lower revs and less at higher revs.
They could have done the same thing with a small restrictive muffler, so why do it this way? Maybe they wanted to keep a larger muffler volume to help with noise and at the same time use the SLR to help past the emissions requirements.
I know if I had such a muffler the SLR would get 'lost'.
EDIT: On second thought, a small restrictive muffler would increase the backpressure during blowdown. They worked around that by having a 'volume' to accept the initial blast during blowdown and then letting the back pressure rise to prevent scavenging losses - I'd still 'loose' the device.
Either way removing it changed everything.
