600 edelbrock secondary bog.

Seems kind of odd that you would get 2 bad carbs, especially the fact that one is new. There are many members on here who have the new AVS2, and are very happy with them. I run the 650 Thunder series carb, and love that thing. I've run the 600 Ede, and love that carb to. This might lead me to look for other issues. Are you sure you have the correct gasket for the thermoquad intake ? And that there are no vacuum leaks at the base of the carb or intake ? This would definitely cause it to run poopy. Have you ever checked the float setting on the carb/carbs ? And I'm not so sure why you would change jets/ springs or anything on the car until you got the car running properly. Ede's are generally set pretty well from the factory. I would go back to all the stock parts/settings on the carb, until you get it tuned properly. With the occasional miss, it could very well be a vacuum leak somewhere.