Possible Sierra reman carb. I have seen a bunch of Sierra remans on Mercruisers, about half of them had a problem of some sort externally or internally maybe I guess quality was not checked after the reman who really knows but Sierra does stand behind their products. Just a jist of it some had very loose throttle shafts some others would not return to correct idle position after throttling up and so on and so on. Just saying to add