Probable cause
-Crap leading up to your carby and resting on the needle and seat, in which causing your needle and seat not to seal properly, put in a fine fuel filter, not those re-useable redline jobs,
-And even though its new, replace your needle (needle and seat), and check your float to see if fuel is filling up inside, may have to replace, this should fix your problem,
Your needle and seat is where your problem is, partially staying open and causing your bowl to fill up with fuel and creating your "dribbling" problem through your venturi,
hope this helps,
cheers!