Fuel leak

Hello I’m in the process of getting an old 1982 kz1000 LTD Up and running and one of the first things I noticed is when I turn the fuel onto pri fuel starts leaking out the filter on the back end of the number 2 carburetor. I was just curious as to if this was primarily from the butterfly valve being stuck open or what the cause of this might be. Thanks!

Carbs gunked with varnish fouling the float valve. This tutorial was originally made for Suzuki carbs but most of the same elements cover the KZ version... zeus.mtsac.edu/~cliff/storage/gs/Mikuni_...Rebuild_Tutorial.pdf

I went through the same thing (repeatedly) on my bike. I fitted a rebuild kit in the tap,twice, cleaned it many more times, cleaned the tank out numerous times and even replaced the float needle valves and seats in the carbs.
The problem kept coming back. Everything would be fine for a couple of weeks,then it would just let go and there would be a huge puddle under the bike.The fuel would leak out of number 4 carb ( I have no center stand . The bike lives on its side stand so I could never understand that one!). Stripped the new engine paint off the crankcase as well.
Anyway,it drove me crazy. I could not sort it. In the end,I fitted an inline tap ( filched from my remote fuel bottle). So now,when I park it up,I can switch the fuel to 'OFF' and it stays off.
Good luck with yours.