Engine stalls upon braking

Poly 318 with Carter BBD 2bbl in a '67 Fury. Car was running smoothly until a week ago. Ran fine at part throttle and cruise, but would idle really rough at a stop light. Took the carb apart, found some sediment in the fuel bowl, so I cleaned everything with carb cleaner and blew everything out with compressed air and put it back together with a new carb tune up kit. Now it idles fine, but even after light acceleration, it stalls. I can't drive it thirty feet and hit the brakes without stalling. Runs fine at idle in Park and in gear, seems to be ok if I let it accelerate on its own without hitting the gas, but will stall if I hit the gas pedal and then stop. Car has manual brakes, all vacuum hoses are good, float is adjusted properly. What am I missing?