It has to be losing fuel or spark unless the exhaust is clogged? I've seen it on modern cars where the cats will close up. Muffler batting? If that's not it, I'd swap the carb. It may have an internal clog in the primary circuit. Also, you may see a spark, but is it strong enough to jump the gap and still on every cylinder? Have you checked the coils resistance?
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
Threaded Mode