Speedfight 125 upgrade options

Had a little search around but anything cylinder kit rated seems to be for the 50ccs. I'm wondering what's the best performing cylinder kit upgrade for a speedfight 3/4 125 (4t) I have alot of experience with 2 strokes and general parts like brakes etc but not so much on 4t engines. What would be a good upgrade and what else needs doing along with upping the CC?
Thanks in advance.

 

Is it EFI or carb engine ? if it's EFI then nothing available, carb'd engine just fit a 150cc barrel, upjet carb and that's about it, exhaust won't help a lot.