Large rpm drop

Charlesvolare said
18* initial, 30* total, all in by 1500-1800. No vacuum advance. Limiting plate in distributor at 12* mechanical advance so I can change that if needed but it seems happy there. Can't run much more total timing with that compression and iron heads.

Have you set the T port synch on the carburetor? If the throttle plates are into the slots over square, that could do it.