I had the same problem ...It's not the carb I had the wires crossed at the dizzy!
Hook up a timing light like you where going to time it ....hit the button get the strobe going if the light goes out when the engine sputters
its a ignition problem. I did that and sure enough the light went out every time the motor sputtered .So I started looking and noticed the wires where backassward.
I so thought it was the Carb...I took the weber apart 7 times thinking there was something stuck in it!
I even dropped the tank and cleaned it!
Needless to say I got schooled this week:)