[PaulProe]

Figured it out - the carbs originally came with 120 main air correctors (all new 48IDA's bought in the box do) and everyone reported don't worry about the correctors, they only affect the high end of the main mix. That is incorrect!

If the air corrector is too small and you have a strong signal (vacuum), it will cause the mains to feed slightly, even at low/idle speeds. And it causes your mixture to run extremely rich. Once I opened up the air correctors to around 200, the mains & idle jets began to operate as you would expect.

As I understand it, the air correctors not only control the high end mix of the mains, they also determine when the mains begin to come on line. Too low and they are "on-line" all the time.

I'm not done yet, but I am once again moving forward. Hope my experiences will help another newbie.

Paul