Mystery solved!! Must read!!!
 

I kinda pride myself at jetting so naturally when I got a 2010 ec300 a few weeks ago I started going threw it. First I adjusted the floats. And then the rest of the jetting. But for some reason the idle would hang a tad. Not a lean idle hang either. The carb was just bring very inconsistent no matter what. Even though the floats were set correctly it would dribble fuel at any angle more than the kickstand. So I used this trick. But it wouldn't seal all the time. That's when I noticed a few tiny pieces of clear plastic in the hole! It's clearly the plastic from the tank when the factory drills for the petcock! Problem solved. I also noticed the air screw was collecting dirt from fuel seeping out. So ill be replacing that too
http://www.youtube.com/watch?v=Kgog_Ng0-2Q&sns=em

Wait.. How would they plastic pieces get past the filter in the tank, unless They are pieces of the filter. I'm gonna take the tank off and pull the petcock and see what's going on

I think you'll find most of us run inline filters for this very reason ;)

Glad its helped sort your issues out

Stock fuel filter comes apart, happend to me found the sam plastic. Put on a 90* in line fuel filter and problem solved.

There are a lot of GasGas tanks with the little filter flopping around in the bottom. It seems to be a 'not quite tight enough' fit on the fuel outlet pipe.