Hey,

check you low speed needle.
if the motor dies in midrange the L needle is too lean.
it doen‘nt mean that a new motor has the correct needle setup. It depends on wich fuel and ratio you use.
Had a new dle20 on test bench last Friday and its factory set H-needle was way to lean by using 1:25mix.

So enrich you low needle a bit and let the Motor run arround 2500-3500rpm for a few minutes and watch if it will die anyway...

Regards, Dave