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Now, I need to figure out what is wrong with the Carter Thermo Quad
carburetor in my 1983 big old Dodge van, engine runs wayyyyy too fast,
won't idle down.

If it's the same thermo quads that we had on some V8's here in the late
70's and 80's, then I can tell you that one manufacturer put out a
"program" to their dealerships on how to deal with issues. I received a
lot of detail from a friend in my car club who worked in a dealership
back around then. It included all details on setup, but can't recall all
the steps. I do remember that the relationship between the primary and
secondary throttle valves was crucial. They were linked by a rod which
had to be bent at a very specific angle so that the secondary valves
opened in the right relationship to the primary opening. If this
relationship wasn't absolutely spot on, all sorts of problems ensued,
most notably a hesitation on transition to the secondary throttles at
highway speeds.
The program gave instructions on how to make a tool to check the bend on
the throttle link. Apparently, you needed to check and adjust that
relationship FIRST before making ANY OTHER adjustments. If you don't,
then none of the subsequent adjustments will be any good.

Here's some info on the beasts;

http://www.carburetor.ca/Tech/Carter...de-Vaanth.html

There's a lot more info on the quads on the net. Just a matter of
finding the info that suits your version of the carb.

I always wondered why they went for a phenolic resin body on the carb
but it seems it was to do with emission control in the early days. A lot
of the vehicles ran hotter then and the phenolic resin kept the fuel in
the bowl up to 20 degrees (F??) cooler than an equivalent alloy body.

Brings back memories of the old days. Most of the rodders here used to
turf the quads out but they weren't too bad if you knew how to properly
set them up.

Here's some tips for the Chrysler versions.

http://www.offroadexchange.com/tquad.htm

Hope this helps

Krypsis

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