You changed the cam correct?
More lift and duration than the crate motor cam had?
I think its fuel related.
Sounds like the power valve is trying to open up part throttle and dumping unatomized fuel down into the intake or drippling out of the boosters. With the car in park have someone rev it up to around 2500 and CAREFULLY lean over the carb and see if fuel is drippling out of the boosters.
If my memory serves me well, you need a power valve with a lower number with a higher lift cam or just take it out put a plug in it then go up about 4 jet sizes and be done.
Goodluck, Charles