I think I created a problem while trying to fix a problem. I thought I had a lean condition and jetted up from 70 to 74 on the primary side. Turns out the #4 intake valve lash was out .007 (solid cam). After adjusting the valves the original problem went away (surging, backfiring when cold) but now if I give it full throttle from a dead stop it stumbles, should I jet it back down to 70?

Probably not a jetting problem. Try increasing the squiter size.

Your right Pat, I jetted back down to 70 and the problem is still there, I think I have some issues with the ignition wires, I'll fix that and go from there, thanks for the input.

What is the timing set at?
I run #74 primary jets in my 3310..carb is all stock out of the box other than the switch to 74's and the 2nd lightest secondary spring..I have never felt a stumble,even with 2.56 gears

I have initial at 20 and total at 41. I think the stumble is related to the ignition wires, this is my first big block and I ordered 90 degree boots instead of straight boots by mistake. The 90 degree boots are pushed up against the header (not the tube, the flat part) and probably arcing, although they do not look burned. I bought the straight boots and will swap them out real soon to see if that fixes the problem.

interested to see if that fixed it, im having the same stumble off the line, it opens up a bit after it gains rpm but dogs OTL

I went through a lot trying to fix mine. I learned from research at Holley & some performance books that automatics, particularly in heavy cars, need more shooter size than stick and lighter cars. Don't ask me why, I don't know.

That said, I've also found that a big part of many stumbles are ignition related - not enough (or too much) timing, or bad spark at the plugs. If that's not an issue, then start increasing your shooter size.

Like mr 4 speed, I have a 3310 Holley, but with 72 primaries - I use a #40 squirter, stock is maybe a 31?

It never stumbled before with this same setup so I'm pretty sure it's the ign. wires. I may not get a chance to work on it this weekend but hopefully soon. I will update when I get it fixed.

what are you all taking about when you say shooter size? accelerator pump spring?

the shooter/squirters are in the throat of the carburetor between the bores/barrels. When you work the throttle linkage they shoot the fuel into the carb.