Shawn:
My thoughts about trying the thinner oil were more along the
lines of the transient nature of your extremely rich condition where the
ratio drops off the scale around 3000 (?) RPM.
It appeared from the dyno chart that the mixture was lagging the
engine speed, so to speak. If the slide is rising to slowly as the
engine accelerates, the manifold depression will be too high, and it
will draw more fuel past the needle. The beauty of a CD carb is that the
slide rises to maintain a constant depression. You avoid the need for an
accelerator pump by slowing the rise of the slide, which temporarily
increases depression and richens the mixture.
I still think it is worth a shot; try it again with NO oil, and
see if it doesn't lean out a bit. The slides will rise very quickly
without oil, and the manifold vacuum will drop, leaning the mixture.
Your discussion of needle shape assumes a constant depression in
the manifold, which is true under static conditions. But when the engine
is accelerating, the dashpot is there to allow temporary increases in
the manifold depression, thus richening the mixture.
All of this is much easier than messing with the needles. And
you can always change the needles if this doesn't work.
Merry Christmas,
Vance
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