Carb leaking

1981 KZ440.  I think this is a stupid question but I'm going to ask it anyway.  I've removed the carburetor, cleaned all jets and passages and reassembled.  Before replacing on bike, I hooked the carb up to a temporary gas tank to check for leaks.  I am getting a small but constant drip from the float bowl drain tubes.  I assume this can only be caused by the float shut off valve not closing properly.  I have new needle valves and have cleaned (polished) the seats.  Is there anything else thatcould cause this leak?  Thanks, Barry 

Not a stupid question at all. 

I think your carb bowl has a vertical brass overflow tube inside which connects with the brass nipple on the bottom of the bowl. 

These can develop hairline cracks which are difficult to see. To check remove the float bowl . Keep drain screw closed.  Attach rubber tube to the drain nipple. Fill bowl with water and blow in the rubber tube while keeping an finger on the top normally open end of the overflow. Watch for bubbles. Just like looking for tiny hole in bicycle inner tube. Been there done that.

If indeed a crack is evident then 3 possible fixes.
Use jb weld and give it 24 hours to set.
Take bowl to a hobby shop and find brass tubing which will just fit over existing overflow tube. Cut to size. Solder at the bottom. I did this.
look for posts from Nessism who has described how to press out the nipple and press in replacement tube.

And of course if overflow crack is not the problem then totally disregard everything above
Good luck


 

If you mean you polished the seats(where the needle sits) then that can be a problem. You may have damaged the seat. If you do have a crack in the overflow tube I have used some Tygon tubing of the proper inside diameter over it which did the trick