Dennis Haynes has done some great emissions explaining, many times.
They should be in the archives & it's worth taking a look.
http://gerry.vanagon.com/archives/vanagon.html

As an example-

 >Date:         Fri, 31 Dec 2010 00:04:19 -0500
 >From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
 >Subject:      Re: Failed emissions testing

Rob
becida@comcast.net
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At  6/10/2011 11:42 AM, Ken Wyatt wrote:
>Howdy vanagonauts,  I'm having trouble getting my 1982 westy to pass
>Utah emissions.
>It sure would be nice to go camping but no
>registration..............  No fun!!
>Ken Wyatt
>82 westy