I have a 03 400 kfx with a the stock carb on it yet. I have been having problems with it leaking fuel out of the bottom of the float bowl drain. I bought a new bowl drain screw thinking that was it. I put in a fuel filter thinking that I had dirt that made its way into the bowl on the carb. I just cant get it to stop dripping fuel out of the drain off hose. Is there something that can be done more than I have been doing besides draining the fuel out of the tank after every ride to stop the bleeding?Most likely it's the needle valve as stated above. There is a small o-ring on it that goes bad and will cause it to leak. You can buy a new needle valve or a new o-ring......just have to get the right size and you'll save $$.
Both mine leaked the same way. Messed with the float a couple times and then did the needle valve and no more overflow. The part you most likely need is the needle valve assembly. The tip of the needle could be worn out. If the tip is OK then it is just the rubber o-ring that is on the needle valve. That will cost you pennies. It worked on both of mine when there was fuel coming from the overflow.
Here is the RMATV Part # 2313370-07G00 NEEDLE VALVE ASSY
You can buy the o-ring at any decent hardware store.

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