Had the same sort of issue with my HOlley 4160. The problem for me was the gasket between the metering block and the rear (stern) bowl. The ones that came with the rebuild kit did not properly fit. Either Holley changed the design of all their 4160, or the marine version is different.
My friend, the gear-head, was able to find the correct metering block gasket online somewhere... you may want to ask your mechanic about this. I wish I had a link for you, I tried looking. If this turns out to be the issue, email me and I'll go look at the part box out in my garage