I'm having a similar problem with my recently rebuilt DT3. The weather has warmed up a bit, today was 20c and the bike will start from cold with the choke on but won't pick up on the throttle for quite a while. It stalls as soon as I try to get some revs up. It was fine a few weeks ago when the weather was colder. Could it be the pilot jet needs to be smaller?
I rebuilt the engine with new rings, bearings and seals, also ultrasonic cleaned the carb & renewed the float jet & pilot jet with standard sizes.

I'm not clear on your description of the issue?  Are you trying to rev with choke on?

If choke is off when your stalling happens, my guess is lean, not rich.  The "a few weeks ago" might be a clue as well.  Modern gas doesn't age well and you might simply need to clean the pilot jet as it doesn't take much to gum it up and restrict flow.  A few weeks of can often result in a need to clean carb.

Maybe move the clip down on the needle a notch to get it through the lean spot is my guess without being there.