I have been working on trying to get my Keihn carbs to quit leaking on the 77 KZ650. The #4 bowl leaked whether the bike was running or shut off. I took the bowl off numerous times and polished the float valve seat thinking that the valve was not seating properly. Well, it still continued to leak. I took the bowl off for what seemed like the hundredth time and put my magnifying glasses on to try and find the problem. What did I find? The carb bowl overflow tube had a hairline crack where it met the bowl and was nearly unnoticeable. Most of ya already know that there isn't overflow tubes available for purchase so I started my quest on the internet for answers. I ran across an article on a Honda GL/Gx website and thought I'd give it a try. I first tried pulling the tube out of the bowl but it broke off at the base of the bowl. I tried the wood screw method of screwing the screw into the hole and pulling out the pressed in remaining tube but that didn't work so I followed the article and used a drill bit to drill out the remaining tube. I then purchased some 1/8 copper tube from a local auto parts store and just like the article said the tube was slightly smaller and would not stay in by itself. Once again, I followed the directions in the article and "swedged" the end of my replacement tube ever so little and pressed it in according to the directions. I then filled the bowl up with water and Viola, no leaks !
I want to give credit to the person who came up with this fix as it only cost me about $2.00 to fix the problem. http://cxgl.wikispaces.com/Replacing+the+Overflow+tube
So if ya have a broken,cracked or damaged overflow bowl tube give this a try. It worked perfect for me!