To help make working on your Mikuni/Solex carbs easier I'm uploading manuals here.
First manual is Type Q (44mm) Solex/Mikuni also known as Type 2. These were fitted to the U20 motors (as OEM) parts for the Fairlady Roadsters.
Mikuni-44-Type2(Q-Type)-Manual.pdf 2.04MB 42 downloads
Full copy of the manual for U20 motors can be found here (this shorter manual for the fuel systems starts on page 80 and goes to page 94 of the PDF not the actual workshop manual).