Hopefully you purchased the correct power-valves that are designed for your carbs - from a place like Daytona. Modern Holley power valves will tend to leak around the gasket. You can modify some with a lathe to "fix" the issue - or just buy the right ones from Daytona or others that know what I'm talking about.
Now back to airflow . . .
You must have removed the carbs from the manifold to change the power valves, which means you also took the linkage off of the throttle shafts. So, when you put things back together the throttle plate alignment is not the same as before . . . which is normal.
Now you need to re-sync the carbs - via tweaks to the throttle linkage and/or linkage arms.
1) You should only have an idle stop screw in ONE carb - we'll call this the FIRST one. Back out the screw on the second one (you'll never use it).
2) Setup the linkage arms to be at about the 2 o-clock position on the throttle shafts. Make sure the arms are tight and do NOT slip on the shafts. Many of the repop arms are of cheap pot-metal and you cannot get them tight enough to hold their position. Sometimes I have to "pin them" with a small roll-pin.
3) Make sure the distance between the centers of the throttle shafts is as close to the same as possible to the distance between the centers of the throttle arms (the ends that attach to the linkage). In other words the lengths of the two sides of the linkage parallelogram need to be the same.
4) Start the car and adjust the idle stop screw and mixture screws on the first carb to get the engine to idle. You can adjust the idle mixture on the second carb if needed - or just turn the idle mixture screws 1 1/2 turns from seated for now.
5) Check the airflow with the Unisyn on the first carb. You need to adjust the air-control component to make sure the red indicator is not sitting on the bottom of the sight glass. I just make sure it is 1/2" or so up at this stage.
6) Adjust the linkage so the second carb pulls the same amount of vacuum. This is done with the linkage, not with the idle stop screw. The linkage relationship to the first carb will be responsible for controlling the air flow on the second carb.
7) Adjust the idle mixture screws on both carbs to get the best idle. Check the airflow and tweak the sync if needed.
8) Lock down the linkage adjustment shaft/nuts for now.
9) Temporarily turn in the idle stop screw in on the first carb to get the engine running at about 1500 - 2000 rpm.
10) Check airflow on both carbs and adjust the linkage so that the second carb pulls the same amount as the first. Lock the linkage down.
11) Back the idle stop screw out on the first carb until you are close to the idle RPM you want. Adjust the idle mixture screws on both carbs and the idle stop screw on the first to set your idle where you want it. If the airflow at idle is the same for both carbs, you should not see gas dripping from the main venturi boosters . . . there should be enough fuel coming from the idle circuits to run the engine.
12) Sometimes you might go through the above procedure a few times . . . especially if you are new to doing it.
You'll find that there is no exact/perfect flow match at all RPMs - so you have to pick a point and adjust them at a given RPM to be as close as possible. I usually do this at between 1500 and 2000 RPM and then recheck at other RPMs. Sometimes I need to schwag things a bit and look for the best match between a few different RPMs.