It has a 4 barrel quadrajet 7029262 I got off ebay years ago and rebuilt with the help of Cliff's book How to Rebuild and Modify Rochester Quadrajet Carburetors. This car was a basket case when I got it. It had a 326 engine with 400 heads, no intake and no carb. Headers attached to the engine and a chrome exhaust tip screwed to the bottom of the rear end with nothing in between. Intake bolts were in the center of the V under an inch of grime. One good thing is someone replaced the 2spd power glide with a TH400. Rear end is stock 2.93 gears.

So I've done everything. Got a 400 engine off some guy out in the desert. Bought a stock intake and close enough carb off ebay. Rebuilt the engine, rebuilt the trans, rebuilt the carb. HEI ignition from summit. New everything over the years. My first time doing all this btw, I just would get a book on how to rebuilt TH400 then go through it for example.

Anyhow so on the carb this was originally from a 428 bonneville. My engine is bored over 0.060 so not far off on the displacement. I basically rebuilt it stock with a few mods from Cliff's recipe #1 in his book. Over the weekend I re-read the book. The accelerator pump works there are the two jets of fuel squirting in as you mention.

Since posting I've improved things by decreasing the vacuum advance and lowering the idle. Found I had vacuum advance turned up for some reason so I turned that down and moved up my starting advance to 15 so there's not such a sharp drop off in timing when I tip in. Lowering the idle I did to try putting the throttle plates in a better position relative to the idle transfer slots. The timing helped the most. It has improved but not completely better

I have a few more things to try. Cliff mentions a tip in procedure to help diagnose or setup the off-idle region which is the issue so I'll try that. This carb has an idle bleed adjustment at the top that I've never messed with so I'll try that. I have a spare pair of jets I was thinking of drilling one size larger to try richening up. Haven't tried ported or no vacuum advance so that's an option.

Acceleration is fine if I stomp on the pedal. The hesitation is only in a certain spot a little off idle if I slowly press into the pedal, like gradually driving away from a stoplight.