When I tune the Webers on my XU1 I use this method:
#Remove all linkages
#Back off all idle screws until they are off the stops
#Turn them back in until they just make contact, then turn them all exactly 1 turn.
#Start the car, it should idle, if not add half a turn to each screw, repeat until you get a strong idle. Doesn't matter if its a bit fast.
#Now you use the carb balancer to check airflow at each carby. You need to move the idle speed screws until the airflow is EXACTY the same at each carb and so the idle speed is at your desired level. I use a tacho to monitor idle speed.
#Shut the car off and reconnect the linkages to the carbies
#The linkages should not move the throttle from the current position as set above. You can set this pretty close by eye but never as accurately as you can with an air flow meter.
#Start the car adjust the linkages so that the airflow setting is even and idle speed as per previously set. My linkages use a threaded rod at each carb that make adjusting very simple. As a further check I increase the engine speed to about 2000rpm and check that all carbs are flowing the same.
People will have some variations to the above but in general terms that's how you use the air flow meter to balance carbs. There's no question you can do it by eye/ear or by using a bit of hose stuck in your ear but never as good as with the right tool.
Set correctly the carbs will be smooth as throttle position increases. If they are slightly out then you'll get uneveness or fluttering as each carby won't be in perfect unison.
This is the tool I use. Cost about $100.00 off eBay.
