Weber Marine Carb on 360 la engine?

I think you are using to ported nipple . The manifold port is a straight through hole .

You can see the light from my flashlight shining through the port.

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The man vac port is on the throttle driver's side of the carb. The ported VA port is on the pass side. Make sure you are checking the correct port. If no vac, then it is blocked.
Yes it's the correct side that I'm checking and the other is ran to the distributor