Motorcycle Repair: kawasaki carbs, bench test, vacuum line

Question
I have a 1980 KZ 750 E ever since i have had the bike it has leaked gas out the overflow i have changed the carbs and it still does it i now have carbs from a 650 on it and it leaks gas while it is running and a little afterward i plugged the vacuum line on the petcock and put it on prime and still the problem priciest i have adjusted the floats and checked the needles but still nothing i dont know what else to do any comments

Answer
If it is leaking gas, I would cehck the following:  Float height. sounds like you already did that, but also make sure the needle and seat are spotless and shut off the fuel when the level is reached.  Secondly, the carbs have an overflow 'standpipe' and on some carbs, these get perforations in them.  So check these pipes really carefully, they may need soldering to get them repaired.  Other than that, unless there is a hole in the float bowl itself, it cannot leak.  Do the bench test to verify that the carbs stay dry when you fill them with fuel.

Good luck,  Jan