Nick---First, bravo for attempting to use the 02 sensor and an A/F
monitor or similar meter for setting the mix on a modified engine. I
believe the "richness" you saw on the meter is what can happen when our
engines are permitted to idle for longer periods. Many manuals then
advises to let the engine run at 2,000 rpm for about a minute to "clear
it out".
It's also possible that what you saw could be that the 02 sensor simply
didn't get hot enough, even tho it showed a stoichio reading. It is
better for accuracy to take the car on a drive of a mile or so, to get a
good heat soak in the exhaust pipe. We know that idling an engine will
eventually cause a temperature drop that could effect the millevolt
reading, unless the sensor is high in the exhaust system (close to the
motor).
I wouldn't mess with the carb settings, based on a cursory finding. One
needs to display the meter so it can be observed when driving under
normal conditions. You'll then get a truer reading of what the mix of
air and fuel is, going out the exhaust pipe.
I couldn't tell you what profile needles are needed when running with
the triple carbs, etc., but know that you'll get a street engine closer
to ideal power using an 02 sensor and an in-cockpit monitor! If you
can't get both a decent idle reading (A/F somewhere between 14.5 and
14.0:1, or 400 to 700mv) and a good power reading when your foot is into
the throttle (between 13.0 and 12.0:1, or 800 to 900 mv) you may have to
modify the air valves to accept something from the S.U. needle
selection. You'll want to pick up the Haynes manual for the S.U. Carbs,
along with the one written by Des Hammill on Power Tuning the S.U.
carbs. Know that nearly all of the principles that work for the SU carb
will work for the ZS' you now have.
Dick
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