TOPIC:

I have a big issue on my KZ' carburetor.
There is like a big leak coming from the overflows tubes untill there is no gas left in the tank. I have tried to close the tubes but it's leaking from the air filter after anyway.
I checked the float needles a few days ago without seeing anything. There was no ring marks or scatch on the taper. I cleaned the float needle's seats too.
Is anybody know if the float needles can be bad with the time (1980) ? Is it worth changing them ? or can it be something else ?

It would be a good idea to replace them. I assume you are talking about a KZ750 LTD four cylinder? There was a KZ750 LTD twin in 1980 also (my avatar on the left is one).
If it's leaking when the bike is not running then either the petcock is on the "Prime" position or it needs rebuilt.
Take off your oil fill cap and take a sniff, you will probably smell gas, which means you really should change the oil before starting the motor.

That stupid petcock operation caused me some problems too.I ended up aking off vacuum hose(which opens fuel flow when engine is turned over or running)Plugged it,removed petcock,removed diaphram,plugged vacuume hole leading to vacuume hose.Now,when i stop bike,i turn petcock lever to run postion,which,after me screwing with it,is now off for fuel flow.When running bike,i use prime.might be less of a pain if you just replace petcock.Then again,i am dealing with an 82 kz ltd 4.could be a different operation than yours

I changed my float needles. It's a cheap fix. Also worth running a Q tip soaked in carb cleaner around the needle seats. Also check the brass overflow tubes in the bottom of the bowls as they sometimes split.