Jerry - remember that when working with an IR manifold, or a plenum manifold with plenums feeding less than 4 cylinders; the air flow requirements for the carburetor(s) increases dramatically.
What do the intake ports on the Atlas look like?
I have not run any of the side-draft Keihin carbs. However in a different lifetime (seems like, anyway) we sponsored a 2.0 liter Ford race car with 4 big Mikuni motorcycle carbs. Tuning wasn't that bad (I had been tuning and synchronizing multiple carbs on British and Japanese cars for years); but one racing season, and the slide carbs were totally worn completely out!
Yes, it ran great; but the next year when the racing body outlawed multiple carbs (because we won the championship) it ran quite a bit better with a single Carter WCFB! We never told them we were going to switch anyway when they changed the rules, so we got to complain about the restrictive rules
(We won the championship again!).
Jon.
