2002 636 Track bike (carby model)

I did a track day at EC last Sunday and the bike ran like a dream for the first 5 sessions, never missing a beat.
However in the last session it started coughing and farting, similar to a fuel issue, but i'm pretty sure it's not a fuel issue. It occured mainly only at high revs, with an intermittent loss of power on acceleration. At Idle and low revs, it seemed there were no problems, however it actually stalled on me on downshifting comming up to turn two and again approaching turn 10
I spoke with my mechanic and he can't look at it until next week, on the phone he said it could need the valves doing
I thought I would see if anyone else has any idea's what might be going on ?????????? Cheers.........
However in the last session it started coughing and farting, similar to a fuel issue, but i'm pretty sure it's not a fuel issue. It occured mainly only at high revs, with an intermittent loss of power on acceleration. At Idle and low revs, it seemed there were no problems, however it actually stalled on me on downshifting comming up to turn two and again approaching turn 10

I spoke with my mechanic and he can't look at it until next week, on the phone he said it could need the valves doing
