Hi, I am running dual 40DCOEs in my 98 Jetta. Heres what I can tell you about setting the carbs up.
#1 There are 4 or 5 books about weber carbs. Buy them all and study them. These carbs are are very subtle and you need to understand how they work before you start working on them.
#2 Buy and install a wideband air fuel mixture gauge. Tho 14.7 is said to be the desired A/F mixture, You will find 12.5 to 13.5 is what works best.
#3 Buy a good selection of jets from what you learned from the books.
#4 Go, if youre like me, in 3 or 4 months you will have them tuned.
The Chinese jets work fine.