What kind of intake runners do you have? The early steel ones had pinhole leaks that would create all sorts of vacuum issues. I had a hairline crack on one of my cast intakes that caused hard starts and rough idle issues. Wouldn't have seen it unless you puuled the carb and intake off the motor.

Also what kind of distributor are you running? OEM centrifugal or 009? If the breaker plate on the distributor (centrifugal) is shot, it won't advance the timing the way it's supposed to.

Also, are you running single or dual carbs?

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car