Aftermarket carb

Thank your friend & tell him to be on his way (that’s the polite version), a 39mm carb is almost twice the area of a 30!

Now 30 is a pitiful size carb to have on a 200, but there is a reason. The rest of the bike will be restricted & this was confirmed when I swung my eyes to the left to see your location is Singapore.

A KDX200 takes a 35mm carb but the SR version (as sold in Singapore) is like a 28 or 30 but there are other restrictions.

Putting a 34 on may not yield results until you replace other parts with unrestricted market parts, probably pipe, barrel & maybe ignition.