It would probably work, you wouldn't gain much without huge valves and a big cam. Being a 2 stroke carb it won't have an accelerator pump, which is why the stock 5hp carb sucks so much.
so how about a 4 stroke 150cc or 200cc carb? the cylinder is 206 cubic centemeters when the piston is all the way at the bottom of it's stroke. a 200 cc carb flows enough to fill this. idk let me know.
That carb is way to big for your flatty nowmatter what kind of cam you got. Small high strung two stroke=huge carb. My rm125 had a 36mm mikuni, my kawasaki kz400 (twin cyl 4 stroke) could handle a single 34 or 36 might be pushin it.
If you want a mik look for something in the 22mm range