Originally Posted by Airhead Wrangler
The r100r has 32mm bings, not 40s. The pistons are not the same as earlier higher output R100s. They have a lower compression ratio of 8.5:1 compared to 9.5:1 in the higher output motors. The heads also changed from large port/valve in the in earlier models to smaller ports and valves in the later models. The exhaust doesn't do anything to meet emissions. There's no cat. Jetting also got leaner from earlier to later models.
According to this, it has 40 mm and the 2 into 1 exhaust has a cat box under though?