2-1 on kz400 with mikuni 32 too big???

Hey guys,
Got a 79 kz400A that I'm building. Trying to get it running right. timing is good, valves are good, gap is good, plugs are good.

I followed a lot of guys builds online with kz400 and 440's where they ran a single mikuni vm32 into a 2-1 manifold with great results. But when I did it I struggled hard. essentially came down to it ran rich at startup and then leaned way out when warm (is that possible???) and would bog under quick throttle. couldn't drop pilot size or i would have to back airscrew too far out.
However, I found blocking the carb throat partially with my hand made it more responsive and let me snap throttle, so I figured it's running too lean. So now have it running actually pretty well with a plate over the whole throat with an 3/4" hole in it! Essentially I'm blocking 75% of the carb opening and its running decent (maybe a little less power than before). What is going on? That means this carb is way to big for the bike right?