Don't know how far you have got, but the carbs should have the rubber bung on the balancing port. If it idles ok the idling jet side of things must be passing fuel ok. Similarly for the blipping, the intermediate jet is passing fuel. That balancing port might upset the main jet (unlikely) but vacuum leaks anywhere are not good news. If someone's tried to balance the carbs with that missing, you'll need to rebalance them when the bung is replaced. Anything that securely stops the flow should do until you get a new one (or 2).