I may be wrong, but my experience with big cams while they do produce less vacuum at idle they also cause the vacuum to fluctuate slightly and when throttle is given the gauge still reacts immediately. And, my experience with vacuum leaks is they tend to like the choke (depending on how large the leak is) as it helps to compensates for the leaner mix caused by the vacuum leak.

Just a thought, by chance is your gauge plugged into the timed vacuum port? And, have checked the gauge for its accuracy?

You may be casing your tail on this, as your question was “can I close the choke completely”, for which Roger answered you correctly, “no, you can not close the choke completely”, with a further description of how to check and adjust the choke.

However, if you are having tuning issues, well that’s a different story and perhaps describing all of the symptoms will enable us to help you better.