Tom,
Sounds like the NV isn't closing off all the way. Try closing it as far as you can and then check to determine if you can blow a little air through the NVA. I suspect that you will be able to; if so, you will probably need a different NVA.
The hole(s) in the spraybar also should be very near the center of the venturi, rather than nearer one side or the other.
Cheers,
Jim