Zenith suggests this unit for engines of a minimum of 300 CID. This carb is the largest of the 228's. It will work well on engines as large as 325 CID. When you open the throttle, vacuum is going to approach zero, venturi velocity is going to be too small, and the engine will run lean to very lean.
Since you have another carb coming, in the meantime when going up a hill, experiment with increasing the throttle only slightly, rather than wide-open. MAYBE with a smaller throttle angle, you won't totally kill the air velocity through the venturi, and the engine will run better than at WOT.
Jon.
