will not start without Starter Fluid help. Runs pretty well once started.
That is the classic symptom of acceleration pumps not pumping. Upon starting, the squirt of gas from the acceleration pumps is the only fuel that the engine gets, as it is turning too slowly to build enough vacuum to draw fuel off the idle or main jets.
When the carbs are removed from the manifold, have some gas in them, and the throttle is opened, you should see a jet of gas squirt out of each barrel, sort of like a water pistol shot. You could try doing that, and see if all four are squirting. Before removing the carbs, you could remove the pump jets, and verify that they are not plugged. Also, remove the carbs' top covers, and observe if the pump mechanism moves down as you open the throttle.
I can't explain why the acceleration pumps would fail on newly-rebuilt carbs. Did the carbs sit on the shelf for some time after the rebuild? If so, the pump mechanism may have stuck due to corrosion.
Runs pretty well once started.
Meaning it idles OK in the garage, or it runs fine on the road? If the problem is the acceleration pumps, it won't rev up smoothly.