I just recently purchase a 2001 400ex and noticed that when I'm done riding and it is sitting gas leaks out of the drain tube. The drain screw is all the way shut too! If I shut the gas off, the gas will eventually stop leaking, it's like gas is entering the carb, going through it, and leaving the drain tube. I rode it a little bit, put it in my garage, forgot to shut the gas off, and went to my buds. When I came back there was a ton of gas all over the garage floor. I'm pretty sure it isn't leaking when I am riding. I need some help!!!

 

Most likely it is the needle valve and seat in the carb.... Happends to everybody.

 

try this, get a blow out nossle for your air compressor, take off the main line for your fuel intak into the carb, open the drain on the bowl make sure all gas is out, hit it with about 120 psi, couple quick shots, see if it fixes the problem