most bike now a days are made to run very lean.. that is to use less petrol then needed.. this while in normal smooth operation is less damaging then a proper mixture settings .. but is certianly not good at abrupt changes to speed..
there are three circuits in normal carburetors.. one is used to contorl the mixture when ur race is 1/3rd second controls mixture from that to a little over half .. the third is to cntrole mixture for 3/4 to full wide open throttle..
normally it does happens when ur carb is changing form full ckt to middle ckt .. there is a small interval of time whre mixture is very lean.. hence patakha.,,
solution is to enrich the two ckts .. main and middle ...
the best try for u is to try if raising the needle in ur carb makes any differnce ?
also make sure u clean ur carb with compressed air... not only ur jets.. i maintin my bike myself but sometime only cleaning carb with comrpessed air solves such issues...
also tighten the exhaust nuts .