[alfa] Re: Berlina Spica adj. w/an O2 sensor

[Vangelis Kokkevis <vkokkevis@xxxxxxxxx>]

In a long saga trying to get my 73 gtv running (and
idling) properly after a complete engine rebuilt, I
installed an oxygen sensor and a Dynograph (Wes'
air/fuel mixture gauge) two weeks ago.  For a novice
like myself I find this device invaluable.  You can
instantly tell if your mixture is too rich or lean
while driving and make the necessary adjustments
without having to worry about causing expensive damage
to the motor.  Like previous posts mentioned, a
regular 02 sensor will only accurately inform you of
one of three conditions:  Lean - 14.7:1 - Rich.  The
response curve around the perfect stochiometric ratio
is too steep and the output voltage of the sensor
quickly pegs to full rich or full lean reading.   A
wideband sensor will tell you how lean or rich you
are, but those are still too expensive to be
practical.  

 While the generally accepted method of setting up the
mixture at 2500rpm might be a good starting point, in
my case it didn't prove to be all that accurate. 
Maybe my pump is worn out, maybe the high compression
pistons/Euro cams/ignition timing change the
parameters a bit, but setting the mixture at 2500rpm
gives me a lean reading under under hard acceleration
until the engine rpms catch up.  I suspect that every
car needs a slightly different adjustment that cannot
be performed in a garage (even with an exhaust
analyzer) without putting the car on a Dyno.  Without
an O2 sensor you have to drive the car around and
"feel" its performace (if you are experienced enough)
or try to read the sparkplugs.  

 In any case, I highly recommend installing an 02
sensor and the Dynograph (or for that matter any
air/fuel ratio gauge) on your car to fine tune the
mixture.  Reading Wes' SPICA manual and the excellent
tuneup instructions in:

http://www.alfaclub.org/

helps a lot.  In my case I got tons of priceless
advice from Tom Sahines and Wes Ingram as well.  I
think I'm finally getting the hang of this. 

Cheers,
Vangelis
Mountain View, CA
73 gtv
83 spider
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