A friend and I have rebuilt 6 or more NH carburetors with those new original style needle and seat valves and they all leak, when properly adjusted, according to the book!
Are we over-looking some detail?
Does anyone understand the problem or know of an easy fix to the problem?
Are they leaking through the valve, or around it? Stan pointed out that sometimes the gasket behind the valve doesn't seal and you have to smooth the bottom of the hole.
I think the third needle here is original. Do the new ones look like it? After having a couple of the rubber tips get stuck, I replaced them with the old type.
I think the third type is the original from a Holly G.
I think the fourth one is the original from the NH.
Try these links,
Steve is correct, that is an original NH needle. I think it would work in a Holley G as well.
See here for how to polish the needle. After polishing the new needle, install it in the seat, in the carburetor, and give the needle a light tap with a small hammer and 1/4" brass punch. That will cause the needle and seat to deform to fit one another.
More info here:
You can use Royce's technique with your old needle and seat and you will very likely solve any leakage problem.