Old question, not sure if you saw answers.
Anyhow, when I checked mixture by reading plugs we called them "plug
chops", because to read the mixture you chopped the ignition, and put
your foot on the clutch and coasted to a stop. All this was when the
engine was warmed up. So, you burned down the track flat out and
killed the ignition and coasted to a stop, pulled the plugs and read
them on the spot. We did runs for full and part throttle, but this was
on motorcycles with mechanical pistons in the carb (i.e. throttle
position is directly related to throttle piston (and needle) height).
With SUs, I guess you'd do it a different levels of vacuum to find out
which needle was appropriate. Repeatable experiments would require a
vacuum gauge I guess.
Anyhow, it was sometimes confusing and I often had to call for expert
interpretation. Some other problems can really confuse the situation
-- doing it propoerly required lots of experience.
Now I don't bother, having found that 2 hours on a dyno can do a
better job, more accurately, faster and I also get a nice graph
showing what my engine does :-) It might seem expensive, but the car
sure runs sweetly and that annoying flat spot dissappears!
cheers, Mike
'79 Rover SD1,
62 AH Sprite MkIIA (2 of),
66 AH Sprite MkIII,
66 spridget racecar + 2 spridget parts cars.
_______________________________________________________________________
Mike Gigante
3D interactive graphics, Virtual Reality, british sports cars, and wine
http://mega.cgl.rmit.edu.au/~mg/ mg@mega.cgl.rmit.edu.au
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