OK, I called the parts store I use
http://www.hondaparts-direct.com/default.asp. They have very good prices.
I take it you are referring to the part that connects the carbs to the motor. Honda calls it an INSULATOR. They list two parts. One of them is discontinued and one is still available. The part that is still available is part number 16212-KAF-000. This will fit all four ports. I do not know why Honda lists two different parts, but I can tell you for sure that on my 1989 CB-1, all the carb INSULATORS are the same. The part costs $7.30.
Brian