Sorry, I'm not sure if I'm quite understanding you. It works perfectly when riding?
So when it gives trouble starting, does it work fine afterward? Cruise, full throttle, mid throttle.
What about before it gives starting the trouble? Does it do anything weird, again, full, cruis, mid.
Do you use the kill switch every time you stop? If so stop using it, Just to rule it out.
(It'd be a ridiculous senario, but hypothetically, it could be a sticky contact in the kill switch, mind you, I haven't looked into the mech on a cbr, but would be an easy thing to rule out)
When it gives you probs, do you hear that fuel pump whine when you first turn the key?
91 octane, you're in North America yeh? 91 AKI is the goods, but 95 RON anywhere else. Same diff. Just different measuring scales. This wouldn't be the prob, just checking.
Does it try to kick audibly when it wont start? Like a car, that doesn't really want to run, but will give you hints that it wants to (If that makes any sense.....).