From: hotrod@dixie.com (The Hotrod List)
Newsgroups: alt.hotrod,wiz.hotrod
Subject: Emissions problems on 1978 ford t-bird
Date: 13 Oct 92 05:28:48 GMT
Reply-To: hotrod@dixie.com
Organization: Dixie Communications Public Access.  The Mouth of the South.
To: hotrod@dixie.com
Posted-Date: Tuesday, Oct 13 01:28:40
X-Sequence: 2653
X-Gifs-To: met@sunset.cse.nau.edu
X-Gifs-From: ftp.nau.edu

Hey everyone - I've got a question that may be better suited for
a alt.autos.repair news group (if one exists), but since the car
in question is so old, I thought I might be able to count on some
of your expertise to get me through this little problem...

I've got a 1978 Ford Thunderbird with a 400 CID engine, Motocraft
2150 Carb with hi-altitude compensator, Air Conditioning, and
lots of other nasty passive emissions gear that really
complicates matters to the nth degree.

I am currently having problems with this car passing our state's
mandatory emissions check.  In a nut shell, it passes all tests
with the exception of hydrocarbons, which it blows far in excess
of 2000 ppm.   A mechanic at the emissions test center suggested
that the problem may be caused by a vacuum leak.  Question number
one:  could a vacuum leak cause excessive hydrocarbon output?

Currently, I have set the idle speed on this vehicle at
approximately 650 rpm (their tests measured 724), and I have set
the ignition timing at 10x before TDC (the factory spec on the
emissions sticker says 8x q 2x).    I meticulously rebuilt the
carb only five short weeks ago, and in the process cleaned the
EGR throttle plate (jeez, that thing was CLOGGED!), and set-up
all the carb parts to exact specs.  

The car is NOT burning oil;  it has however been running rich (as
evidenced by a large buildup of carbon deposits on the plugs).  I
have screwed the idle mixture screws in ALL THE WAY, yet the
exhaust still smells like a rich mixture is getting in there. 
Incidently, the choke is electric, and is operating well within
specs;  I have in fact kept it wide open while all this is going
on, and still its rich.  

The ignition is electronic (duraspark II or III - the common of
the day).  I have replace the stock plug wires with an 8.6 mm
high performance cable, and all plugs are firing.  The plugs are
nippendenso, approximately a medium heat range.   Compression
seems to be good on all cylinders.  

Despite all of my tender lovin' care, the car still seems to miss
a little bit, its a little difficult to start (due I would guess
to my cranking the choke fully open), however, once it get over
about 1000 to 1200 rpm, it runs smooth and has no problems.

Question number two: how do I decrease hydro carbon emissions on
this car (assuming that I've plugged all the suspected vacuum
leaks)?  

Question number three:  will increasing the idle speed to
approximately 1000 rpm and retarding the timing to 6x before TDC
reduce the hydrocarbon emissions without throwing other things
(like NOx's, CO, etc) out too far (ie, the max idle speed allowed
is 1200rpm, the Avg CO is 4.5 - this car emits 9.25 - etc)?

In addition, since this car still seems to be running rich, I
suspect that I may have some internal problems in the carb -
potential flooding due to some crap stuck in the metering jets or
the float valve.  Could this be a plausible explanation for the
problem?

Please E-mail me directly at MARKM@TRITON.UNM.EDU with any
suggestions or info;  all replies will truly be appreciated!

MARK F. MITCHAM

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Posted by: emory!lynx.unm.edu!triton.unm.edu!markm ()