A couple of things happened here. One of the main ones is learning to know when this might happen. I now this is an issue and deal with it accordingly. The first thing to realize is they are cast metal and have a tendency to do what we call "outgassing" which is a process when the cast metal cools in the molds the metal shrinks and seals in gasses and casting debris in the pores of the surface. When that piece is thrown in the oven at 400* those pores open and release the gasses and debris. That's what caused all the bubbling in the finish. Add to that an improper media blast texture to hold the powder and then way too much powder will result in the posted outcome. After cleaning the part put it in the oven at 450*-500* for one hour do be sure any pores that may open at 400 will have opened and purged the debris and gasses. at this point you need to media blast all the crap away. Other parts might get an RO primer that aides in reducing the outgas issue. But with the primer, chrome and clear on a carb you are just asking for problems. Also, that carb is not disassembled fully. I would never coat the bowled carb assembled with the clip. It fuses all those parts as one. I would also pull my plugs before putting it in the oven. Once cured and you pull the plugs you will have a ragged edge of powder there that now needs addressing. if you pull the plugs before hand, or as the powder starts to flow, the edges will flow smooth and clean.
Without B17 stripper I'd say that carb is a throwaway unit at this point.