I have had a bog on my 400 for awhile. I believe I have it narrowed down to the accel pump might be a little on the lean side. It backfires from a complete standstill feathering helps.
What parts do you need to change in order to richen this up? runs great except for the little bog.
400 /727 256 comp cams 14* timing light springs
idles at 650 - 700 rpm holley 4160 carb running 5-6 pounds fuel pressure
thanks Mike

Yes, that would be lean running off idle.
Get the accelerator pump cam assortment kit for holleys from summit, and get a jet kit too.
Start by bumping the primary jets up 2 numbers, and installing the blue or orange accelerator pump cam.
And of course make sure the accel pump linkage is properly adjusted as well.

If it is still a little lean after that, bump the jets up another 2 numbers, and you should be golden.

Oh, and make sure you have enough timing too. (which you will also be able to get away with a little more of with more fuel delivery there.

Good luck.

thanks. I looked at summit, just wasn't exactly sure what I should look for.....

Increase the idle to 1000 rpms. Does it still backfire or bog at WOT? If you cured it with a higher hot idle it is timming and not fuel related.