Leaking carbs – Mikuni BS34 on GT750

I went to take the bike to get registered the other day but noticed there was a significant amount of petrol leaking from the carbs. It's a Kawasaki GT750 with Mikuni BS34s.

It gets worse when I switch to PRI. I've recently rebuilt my carbs so they're pretty clean and I have the vacuum caps on 3 carbs with the vacuum tube connected to the tank. The attachment shows exactly where the petrol is leaking from.

Any suggestions on how to fix this?

Where is it leaking from the carbs? Fuel inlet tee? Coming out of the bores? If you can't determine where the leak is when it is mounted on the bike, take them off the bike. Mount them to a rack holder (if you have one made) and hook it up to an auxiliary tank. You can control the off/on flow by raising or lowering the auxiliary tank above or below the carbs. Have a pan below the carbs to catch leaking fuel. You should be able to see where it is leaking from. But by what you describe, your petcock is leaking; which is problem number one. Your second issue is the carbs are leaking from somewhere as well. Which would could be the fuel tee or a stuck float.
You can easily check petcock by taking the fuel line off at the tank and seeing if it is leaking. You should only see flow when you put it on PRI. Good luck.

looks to be float/ needle related ...........if your tank has rust in it..... possible red rust/ dirt, debris in tank ?
incorrect float height/level.........bad fuel needle seat. :S