Check the needle valve. If you see a polished ring around the pointy part, it's likely that the needle seat has been distorted, and your needle's not metering with the needle, but with the end of the threaded part. We usually see needles at about 1-3/4 turns out from closed when leaned to peak RPM.

You may need a new carburetor body, if that's the case.

Please, also check the rocker arm/valve clearances. They will tend to open up a bit as a new engine breaks in.