KZ400A Way too much fuel?

I have a 77 kz400a twin. I got it torn apart and I've rebuilt the points, had the head repaired, checked the cylinders for scoring, fixed some bad wiring connections, replaced the spark plugs and fuel lines, and recently cleaned the petcock valve and the tank. I also cleaned the carbs and made sure they were sealed. I got it with one fuel line hooked up. Tank to carb pickup and that was all. When I accelerate the motor, it reaches about 4k revs then starts spitting black smoke and unburnt fuel. At low revs, it runs very rich. It will not exceed 4k revs. Several days ago while checking the ignition, I accidentally left the fuel on OFF when I started the bike. As it ran out of fuel, I could rev it much higher and it ran much better. I assume this is a carb issue, and I admit I have little knowledge on the diaphragm system in the kz400 twin carbs. It doesnt appear damaged and all the holes are clear, that's all I know for sure. Any pointers are appreciated, and the manual at kz400.com wasn't a ton of help in the troubleshooting dept. Thanks guys.

A couple things to check - make sure the chokes are functioning properly and turning off all the way; perform a clear tube test to ensure the fuel in the carbs is at the correct level. Ed

Thanks. I checked the chokes, they are turning off all the way. Would the wrong fuel level in the carbs mean the floats were poorly adjusted or defective? A friend just told me that could be the problem.

It's unlikely that a float would be defective, although I suppose anything's possible. If the fuel level is too high or too low it most likely is the result of someone bending (on purpose or by accident) the tang upon which the float valve needle rests. Of course, another possibility if the fuel level is too high is that the float valve is not sealing properly and is allowing excess fuel to enter the carb. This case is often accompanied by fuel dripping from the overflow tube. The clear tube test should show if he fuel level is correct. Ed