I'm not potty mouthing the expert, but I think that he might be overlooking a little quadrajet quirk of wich few people have been able to figure out. (I found this problem by pure luck.)

I had that problem with the feul bowl flooding, and dinked with for months. I went into it a bezillion times, swapping needles, seats, floats, and float settings.

One time when I opened it, I touched the float hing and its seat, and I noticed that the Jesus clip--the clip that slips around the hinge and clips to the seat--caused the needle bind in the seat. As a result, the needle was sitting cadywampus so that it wouldn't seat. I threw the Jesus clip away and never had the problem again.

The Jesus clip serves no purpose because the needle cannot escape, so the next time that the ol' quad floods, remove the Jesus clip and see if the problem doesn't go away.