I didn't know the engine died at any setting below full throttle. Your post stated it died below half throttle. You did take the pump apart, was there any foreign matter in it? Did you turn the painted adjusting screws? Are you using a filter and have you checked to make sure it is clean?

I read thru the instruction manual again. With the needle three turns out can the engine be made to run rich? Do you have fuel flowing thru line D back to the tank?

I noted that the pump is used under license from Perry. Maybe you could contact Perry/Conley and see if they have any info on these old pumps.