TOPIC:

You don't HAVE to do all six if you're syncronizing the carbs since there's no adjustments you can do between adjacent cylinders on the same carb. Some who have the equipment to look at all six inlet pressures at the same time do, because the differences can indicate certain things like a tight intake valve or poor cylinder filling. But the primary reason for checking the inlet vacuum is to balance the carbs.

Got it!
thanks