Yea i noticed that. The bore kit comes with a Race mapped CDI unit aswelll. Aparently acording to some one on this topic (i cant remember who) said that the race ignition unit made the R125 do 90+ mph so with that and the 170 big bore kit for the yamaha i guess you would be looking at about 110+ MPH maybe more but im not sure to be honest. The down side to that 170cc Big bore and the race CDI unit is that it costs £500. I have already spent a fortune on my R125 with the Micron exhaust costing £300 and i do not really want to be spending much more on a 125 when i can wait and save up for a bigger bike. I dont think its worth spending aload for a 125 also considering its my first proper bike otehr then a ped.
Also you was talking about that air recirculation box that is connected to the standard exhaust. When i bought my exhaust system it came with a plastic bung and instructions saying to seal the pipe that connects that air box to the manifold/mid pipe. I asked a few mechanics aswell and they said this should release maybe a few BHP probably about 2 or 3. Its not much but its something. The most i have had out of my R125 with the exhaust system is 84 MPH i could have got more but i didnt push the bike into redline because it dont sound healthy lol.