I haven't seen it mentioned here, so I think I'll add it.

Had a quadrajet on my 360 and while rebuilding it, found a resource that had a lot of information on repairing the deficiencies that most q-jets had:

Casting plugs in the fuel bowl tend to leak, causing the carb to "empty" while it sat overnight. Epoxy around them cured the problem.

Throttle shaft bushings were almost always worn out. A kit with new bushings and the correct drill bit is available.

The main body tends to warp after the carb has been apart a couple of times due to overtightening of the longer bolts in the front. Even the lower portion can begin warping. Either straighten yours or find a donor for the main body.