From: markm@triton.unm.edu ()
Subject: Emissions problem on 1978 Ford T-Bird
Date: Tue, 13 Oct 92 04:31:51 GMT
Organization: University of New Mexico, Albuquerque

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 10 before TDC (the factory spec on the
emissions sticker says 8  2).    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 6 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

Newsgroups: alt.autos.antique