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SUs take some time to learn but it sounds like you are on the right track.

The most critical thing to know about SUs are that they are entirely dependent on the condition and tune of the motor. You will never get the SUs right if your valve lash is out of spec or your timing is off. These make the "suck" and if "the suck" is uneven the SUs will not function correctly no matter what you do.

Synching those carbs will require you using a length of hose to listen to the "hiss" or you'll need a carb synchronizer to get the idle/suction for each adjusted to the same level.

Basically you want both the carbs pulling equal amounts of air into the chamber.
Getting this right should make the pistons move equally. If they still don't move in synch there are some other things to follow up on.