Hi David,
to put a complete carburetor in an ultrasonic bath isn’t the correct way to handle that.
At least the top cover and slide with membrane and the fuel float bowl shall be removed.
Bad starting and idling is often caused by a clogged pilot jet (#45?).
You may remove it from the carb body and clean it manually.
Have you seen the carb assembly photo story on the german Z750Twin website ?
https://www.z750twin.de/vergaser.htm
There you will find also this picture showing the pilot jet and its position.
From my experience this is the culprit in many cases.
Cheers, Michael
