kz550 vaccum operated petcock aftermarket tank

I'm new to kzr and i apologize in advance for dumb questions. I'm building a hardtail kz550 bobber and i have an issue with the tank i intend to run.It's an aftermarket tank for harleys and has the harley screw in petcock inlet.I have it hooked up and my carbs have been leaking fuel.My question is,is there an aftermarket vaccuum operated petcock that will function like the original? Is it the float valves? or am i boned?I don't have the original tank and i would rather run something else.

If the carbs overflow for a brief period then stop, then that means the floats are set wrong or the float valves are leaking, or even possibly that there is a cracked overflow pipe inside the bowl.

If the carbs keep leaking for a long time, then the petcock is also bad in addition to the carbs.

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Very good advice guys,thank you.I did clean out the tank the best i could and used seafoam in the fuel beforehand.This is my first complete basketcase project.I knew it was going to be a challenge.The carbs need to be gone thru and adjusted who knows how long it's been sitting neglected.

Forgot to mention, you can find links to a lot of 550 info in my signature.