Still More Re: (followup) Re: Alternatives Re: <VV> Rebulding Retard?

[FrankCB at aol.com]

In a message dated 2/22/2007 2:54:18 PM Eastern Standard Time,  
burkhard at rochester.rr.com writes:
 
[SNIP]

The  engine would run without 
vacuum advance (i.e. like a dog) until it got  warm enough and then the 
thermal switch would enable it.  Under  retarded spark, engine out NOx 
is reduced because peak combustion  pressures are reduced (which result 
in lower temps and *that* reduces  NOx). The retarded spark also 
*increases* the temperature of the exhaust  gas which yields some 
improved oxidation of HC / CO prior the  catalyst


[SNIP]
 
    It sure helps to have an automotive engineer  available to clear up this 
stuff for us mere mortals<GGGGG>
    Jim's explanation reminds me of the days long ago  when I had to get the 
1965 Corsa 'vertible (now his "Purple Pylon Eater") pass  NJ State inspection. 
 Those days the emission check was done only at idle  speed, so I would drive 
the car to work in the morning.  At lunchtime I  went out in the parking lot 
and "detuned" it by retarding the spark close to TDC  and leaning out the mix 
both done to reduce emissions.  This of course,  dropped the idle speed so low 
that it was necessary to open the throttle plates  on the primaries 
significantly.  Unfortunately, when I did this, the vacuum  advance ports were 
uncovered so the full vacuum advance occurred, defeating the  attempt to retard the 
spark.  That was solved by simply pulling off the  vacuum advance tubing and 
plugging it.  That left the poor 140 with  retarded spark and NO vacuum advance.  
Driving it a few miles to the  inspection station the car felt like it had 
only about 50 hp.  The 140  would pass the emission test, I would drive it back 
to the parking lot at work  and restore the timing, the vacuum advance and the 
mixture back to normal,  thereby restoring the full performance of the engine 
at least for the next  364.9 days before the next inspection!!
    So if you have trouble meeting any IDLE  emission checks, I still 
recommend this procedure. 
    Frank "occasionally law abiding"  Burkhard 
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