First Generation Firebird-L Mailing List
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Thanks Thomas,

I did quite a bit of searching before posting here but I guess I just wasn't
typing the right search terms to come up with the right info.  I appreciate
your knowledge.  The link you sent was informative but isn't quite getting
me the answer.

- There is only one vacuum port on the back of the carb, dead center below
the throttle body at the base of the carb.

- I wouldn't have thought anything strange about the vacuum going straight
from the carb to the distrib. advance except that the service manual info,
and other stuff I have found has the vacuum going from the TVS to the
advance port on the distributor and not straight from the carb.

Thanks for helping a Firebird newbie (and a carb newbie).  I'll keep doing
internet searches as well.  Just setup a PC in the garage high on the
workbench at the front of the car so I can look stuff up without running in
and out or having to print things.  :)

Danny Dutch
[email protected]


On Wed, Sep 2, 2009 at 3:28 AM, Thomas R. <[email protected]> wrote:

First Generation Firebird-L Mailing List
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Danny,

On a Quadrajet, the lower port on the front driver's side the hookup for
"ported vacuum", and it commonly goes straight to the distributor only.
This ported vacuum lies above the throttle blades, therefore, at idle, this
port has no vacuum, since the throttle blades are closed; and hence it does
NOT pull your vacuum advance ahead.  But, when you press on the accelerator,
the blades open up, vacuum is then present at this port, and then your
distributor kicks in the vacuum advance.

The port on the back of the carb at the base is "manifold vacuum".  This is
always on.  This gets hooked up to your brake booster, or any other device
in the car that always needs vacuum.

The hard line to your trans should be for your TH-400 tranny vacuum
modulator.

The other port at the back should go to your secondaries choke pull-off.

Read this thread for more info:
http://www.chevytalk.org/fusionbb/showtopic.php?tid/214605/

Not to say we can't help you, but there is a WEALTH of information at your
fingertips on the Internet.  Utilize Google or any search engine to look for
info, which is how I found the article above.  Search "quadrajet ported vs
manifold vacuum."  Remember, lots of these GM cars have similar parts, so
you don't necessarily need a Firebird manual.

Ciao,
Thomas

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