Can a carb be tuned with an A/F gauge

It's a really good tool to have. Put a bung in each headpipe and compare sides. Look for best results by performance for WOT, and not tune to a predetermined number. This is where going to the track is very good to have. You'll find the number the engine likes best for max MPH.

For idle and cruise, shoot for around 14:1 for both. Sometimes you can't get there without some issues. You can see lean/rich spikes when applying the throttle, etc. and make adjustments.

If you have a holley, learn about what each circuit does and where it comes into play. you can tear your hair out trying to tune it up! :)