Priobe
while your displacement is about the same, your cam is much wilder (mine is a straight cam with about 225@.050 in/ex) and your compression lower (10:1)
Even whitout seeing your lm-1 data I would rule out ignition as the primary cause. Btw, the MSD stops beeing a multiple spark unit at about 3000. Its just single (long duration) spark from there on up.
Jac already pointed out why, both your Idle & Main are leaner than mine.
With the wilder cam and lower compression, it most probably will need a richer mixture that what I am running.
Depending on what parts you have on hand, I would start by reducing the Venturi size to 40. Donīt go to 37mm that is way to small even for my motor.
The stronger signal from the smaller Venturi will allow the transition circuit to kick in earlier.
As a next step I would reduce the air corrector, too big an air corrector will slow down the kick in of the transition ...
Just make sure to do one change at a time - I use an Excel table to keep track of the changes - at my age I tend to forget quickly
