If the float level is not set correctly or something (dirt,rust,or other crap) is keeping the float needle valve from closing when the float rises, fuel will continue to flow into the carb and run out into the intake.
Did this condition just start or has it been ongoing? Also, do a site search. There are a couple of threads about jetting and changing the 38 DGAS emulsion tubes to size F-66.
this just started today when i tryed to recalibrate the carb. i hav already rejet the carb to 150 and F66 e tubes. i drove to work and it was still burning rich, but idled ok. now when i set everything to base line, it idles at 1800
I agree with Gary's float comment. Apiece of dirt, gasket material, anything could hang up the needle seat. If that's not it, then you could be pulling gas from the bowl from intake vacume due to a gasket breakdown.
Webers MUST have a fuel pressure in the 2 1/2 to 3 1/2 PSI range as anything above 5 psi will cause higher fuel bowl levels due to the float being overcome with the pressure and the fuel continuing to seep into the bowl past the seat.
If the needle is not being held open by debris of some sort or a lump of gasket etc. then check fuel pressure.
my recient work has been a Crane 700 ignition and that was when I noticed it running bad. i am running fuel pres at 4 lbs which will be down to 3 lbs tomorrow. i will chack your other ideas too. i was very care full when i replaced the power valve to keep things clean, but you never know.