Interesting it says bore is 47mm meaning that Super power is 72cc.
Is 72cc also written on head ? or does it say 78 cc ?
Cause if it's written 78cc than the bore should be 49mm.
Anyways as for your problem 46kmp/l from a chonda is good, dont expect more. If you need to set valve clearance you are going to need a feeler gauge to set it to the prescribed 0.05mm, but i highly doubt that it is going to effect your average.