I have a hesitation right off idle to 1300 rpm's. Its actually more like a stutter, It will clear it self out past 1300 rpm. It wont do it under real light or hard acceleration. I have a very good understanding of the carb but just cant figure it out. The engine is a 350, msd ignition, 600 cfm carb, comp cam magnum 270. I have about 12 deg. timing at idle (with unhooked vaccum advance) and the vaccum advance hooked up to direct manifold vaccum which brings it up to about 26 deg at idle. I tried adjusting the pump shot and jetting with no luck . My assumption is that since I have poor vacuum at idle due to the cam (11 hg), it is confusing the idle to primary circut, make sense? Also guys please dont tell me to replace it with a holley because I cant afford that option right now:)

does it affect it any if the vac advance is disc? are you using ported or direct vacume?
11 hg sounds kind of low for that cam, kind of getting to could there be a vac leak-does covering the carb kill it right away?
in a vac. state, the metering rods should be sucked down to the fatter part of the rods-the vac has to be strong enough to overcome the springs-if your in a lean condition when the problem occures, maybe a stronger spring might help the transion to rich-what is the vac when the problem occures, this might give you a clue whats going on-do your mixture screws give you some control, maybe turn them in to a little richer-of course we are going on the assumtion the carb is the problem, not something else like dist, tight valve, or comp.
loss

I do not think you need a stronger step-up spring until you try more timing

Try more initial timing such as 16 degs. Set the timing there then back down the idle speed, recheck timing, adjust dle speed again....when you have it idling as low as possible adjust your idle mixture screws.
......btw, ensure you limit total timing to 36 degs initial plus mechanical.

I had fun setting up my 800 Eddy a few years back....
How far out are you idle mix screws?
Ho long has the carb been on the car?
Filter changes?

Im using direct manifold vacuum. Im using 12 intial and 36 total. idle screws are where they should be and respond when adjusted. I have tried the heavier springs without luck.