does gas burp all over the side of your 80-87 van then you fill it up at the
pump?   heres the answer to your problem.   get the 88-91 filler neck w/
shutoff float ball..
heres one.. not mine..
http://www.thesamba.com/vw/classifieds/detail.php?id=195304

i installed one of these on my 84 van and it solved the problem instantly.
easy install, too. dont need to drop the tank or anything.
chris