What kind of air cleaners are you running on this beast? Those little "hot rod" Mr. Gasket air cleaners don't flow enough for even a 216, I lengthen the center rod and run 2 elements stacked for enough flow, otherwise you choke the carb and encourage leaks.

Squint down the back carb throat while it is running and see if you see gas or vapor dribbling down there. If so, you have a float set too high and you are dumping fuel into the intake. Rochesters can be real leakers.

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