Would be a good idea since the 144 piston will be heavier than the oem cast piston. the oem crank should be already balanced to the oem piston but that is not always the case.
I just asked Eric Gorr the same question. He said the piston he puts in the 144cc is the same weight as the stock oem 125cc piston, so balancing was not nessary. This however was on a yamaha so I dont know if it would apply to kawi.
Necessary no, nice to have, absolutely.
My 314cc stroker kit has a balanced crank and it completely takes away most of that 2 stroke vibration.
2013 KTM 250SX stock
2008/ 2013 KTM 250SX. An '08 BUT w/ the wheels, forks, crank, entire top end, carburetor, exhaust system off of a BRAND NEW 2013. Also has MX Tech shock, Hinson basket, hardparts 22mm. This bike is currently FOR SALE. PM please.