John M. brought up a good point about the throttle plate being closed.Several years back I
had a 1970 Chevy pickup with a 250 that had a cam similar to yours and a stock intake that I had modified to accept a Rochester 2 bbl. It
had idle issues similar to what you describe. I found the throttle plate was open enough to uncover the slot for the transition circuit and
producing a rich condition at idle. On advice from a friend I drilled a small hole in both throttle plates(don't remember the size)backed the idle speed adjusting screw out and readjusted the idle mixture screws and it cured the problem. I know this is not an apples to apples comparison due to the different intake,carb and engine size,but would be easy to check while the carb is still on the engine.
Just a thought.
Gordy
