leaking gas from over flow tubes

I have a 1979 Kz650b that is leaking gas out of one of the carburetor over flow tubes after I have stopped and turned the engine off. I read in a KZ forum that it was probabally a stuck float and one way to free it up was to blow air up the over flow tube to free up the float. I did this and it seemed to wor k for about one day before it happened again. My question is why when I blew the air up the hose ,did gas come out of what I think is a vacuum nipple. Should there be a cap on those, the other carbs don't have caps either.

The fuel probably came out of the bowl vent tube. It is supposed to have a hose on it, but it is not necessary for the engine to run. Some models have four of those, others have only two, one between carbs one and two, he other between three and four.
There are also four vacuum ports. One should be connected to the vacuum line from the petcock. If the bike has the Clean Air System in place, two of the vacuum ports will be connected to it. The last one will have a rubber plug over it.

I cannot imagine how blowing air into the overflow could fix anything.

Sticking float needles, warn float needles leading to a high fuel level, and cracked overflow tubes are a few of the common causes for issues like this. You won't know which until you break down the carbs and go through them. Doing a project like this is the right of passage of owning a 40 year old motorcycle and you will reap years of benefit if, and only if, you do the job right. Know going in that purchasing aftermarket "carb kits" is not necessarly the proper approach. I advise to take the carbs fully apart and then take inventory of all the soft parts like gaskets and O-rings you will need, along with any hard parts, like float seats, that may be needed. You can purchase the real deal Mikuni float seats off Amazon or Dennis Kirk for good prices. Those are superior in quality to any aftermarket "carb kit" equivalents you will find. The devil's in the details so do some research and do the job right the first time to save effort in the long run.

Yours should look similar to these.

I never said thank you but THANK YOU

You are welcome. Did you solve the problem?

In addition, when disassemble the carbs make sure you keep the float, float needle, and float needle seat for carb #1 together with #1 carb body. Same for the other 3 carbs. Those three items are best keep in the original sets. All the rest of the brass parts can be tossed together and cleaned as a group.