The twin 6 v12 is using a single rotary type walbro clone carb mounted atop of a large induction plenum manifold.... there is so much ring drag from all 12 cylinders it refuses to accelerate... ign timing is off as well, very laggy throttle response, hard to tell due to the internal resistance.

Those rings are too stiff, and over tensioned... same with the v12... its a conversation piece for the most part... I'm sure it can be improved upon... Their V4 was probably their best performing engine.

Have fun, something to tinker with