Edelbrock part throttle surge help

Update...
Installed a fuel pressure regulator and adjusted pressure to 5.5 lbs at idle. Replaced the metering spring to the 8" one (silver, i believe) and neither of these affected the part throttle surge problem. I also disconnected the vacuum advance with no effect either.

When i check timing advance, the timing increases nice and smoothly as i increase the engine speed, so my mechanical advance doesn't appear to be a problem. Would too much initial cause this problem maybe???? I need to check it again (!) but my recollection is that i have ~15 initial, ~15-18 mechanical (i welded the advance plates).... Running out of ideas guys!!!!!! HAHA I've never had trouble tuning Holley's so this is getting frustrating.... Give me some more ideas before i ditch the carb and slap a spare Holley 1850 on there! Thanks in advance...