There are three possibilities

Carb is junk

Timing is wrong

Cam is way off

Thats it. If the carb is good and a pro built the engine you most likely have a timing issue. Why are you trying to get the drive gear so that the slot is parallel at TDC #1, shouldn't it be perpendicular? Did you VERIFY that its no 180 out (have to ask because people are always CERTAIN that they didn't install it 180 out). Did you check TDC or are you assuming the balancer is correct?

Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street