it's getting air leaks from somewhere.
Or there's debris in the needle valve's jets or nozzle
You can try cleaning it out using a little guitar string or a single strand of wire.

I had an engine that was doing that. i actaully saw fuel coming from the LSN.
So I put ca in it..lol it'll run good for 10-15 mins...but at least i knew that was
the source of the engine's eratic behaviors.

Also makesure the o-ring on the needle is still good and not dried or damage.
If you soak the carb without removing that little o ring on the needle..it might had damaged it.

To isolate the problem of posisable leaks coming from the throat, you can tried JBwelding it.
Double up on the Oring or do both.