After each idle re-tune, you must set the H-needle again. It seems you are too lean on the top end, and your mixture is mostly provided by the idle needle.
Set the engine at ~1800 with the idle stop screw. Then find best idle rpm with the idle mixture needle. Open up 1/8th turn from there.
Now turn your attention to the high needle. close until rpm sags, open up again until rpm is just a tad off max rpm. If the carb is OK, transition should be OK. If not, dismantle the carb and clean the transition spray holes well. Blow some fuel in the carb and check function of each jet. There should be three or four of them, apart from the main jet.