Has anyone changed out their rear master cylinder? Mine has been really weak since new. I've changed the fluid twice and vaccum bled them 3 times since then [at 37,000 miles now] and its never changed. I have 2 friends with f4i's and they feel the same. I've ridden a bunch of 03-05 r6/06-09 r6s's and they all have much better pedal feel. Has anyone ever swapped theirs out?

 

i havent, but that shouldnt be hard to do-especially if it matches the mounting holes. mine feels fine, but i do understand what you mean, ive felt much stronger ones.
its one of those things like the front brake master and clutch perches, they are pretty much universal.(to some extent)