[Greg56]

I have a 400 small block chevy, bored 40 over, a 458 lift cam, edlebrock airgap rpm manifold with a 1407 edlebrock manual choke carb. Ever since I put this all together,(over a year) the engine stumbles to the point of dying if I floor it and don't let off.this will happen off idle. It also stumbles when the vehicle's moving, but recovers before it dies.
I thought I had trash in the carb from some gas I got once that had trash in it enough to dirty 2 fuel filters. I've completely torn down the carb and cleaned it, and even though it didn't look like it needed it I put a new acelerator pump in it. I've moved the rod to the pumps arm up and down in the three holes for adjusting pump stroke. I've also had the timing everywhere you could imagine by advancing the distributer to the point of it making the starter drag to the other end until it backfires back through the carb. I've changed the springs on the curve kit, and adjusted the vacuum advance to so many combos I couldn't even try to list them.
Can someone please give me some suggestions about what might be causing this. something aside from the typical holly fan telling me to get one of them.
Any insight on this will be greatly welcomed, I'm running of of ideas.

[Shortstep]

What type if ignition are you running on this setup and are you sure there's enough gas coming into the carb? Manual or electric fuel pump? What type of vehicle is this in?

[lluciano77]

Set your distributor advance at 18o with 16o initial. If the problem is still there it has to do with carb tuning. Buy a vacuum guage if you don't already have one. Set your mixture for highest manifold vacuum. If that doesn't do it I'd go Holley.

[Greg56]

Shortstep, I'm running a GM HEI distributor with a 50,000 volt coil and matching ig mod. It is a manual fuel pump, but it stumbles imediately when I romp on it.there's still plenty of fuel in the accelerator pump. the truck has plenty of pep as long as I don't try to come out at full throdle. It's in an 85 GMC Sierra Classic, SWB. has 373 locking differential rear end.
Illuciano77 I'll be able to manage setting the timing as you've said, I don't know what it is now. Did it by ear and test runs. But as to the mix you're talkin about. I am ignorant about that. Please explane in much more detail. I'm not nearly as experianced as as you and many others here.
Thank you very much.