Yamaha/MBK 100cc manifold and carb question

Hey folks.

Working on an MBK 100cc 2 stroke (nitro/neos etc) to fit into a Honda Zoomer and would like suggestions on a suitable manifold and carb set-up (from the SIP store of course). 

May go up to a 110cc cylinder in the future, so what size (20, 21 or 25mm) intake should I use.

Any info will be very welcome, cheers. SJ