1973 Plymouth Scamp accelerating/braking issues, please help

Ditto on likely the carb. My 69 Slant w/ Holley 1920 acted like that for many, many years, despite many intake and engine changes and even a new long block. Finally tried a ~4th carb and it ran like a dream. The others must have made it idle lean. I now have a slant again, a 64 w/ Carter BBS and it idles so smooth you can hardly tell the engine is running. The BBS appears more approachable (judging by the manual) with all internal parts visible, unlike the 1920 w/ sealed metering block, but I haven't opened it up yet. Some people like the Holley 1945. A few like the 1920, but must have lucked out (like my last one). I have read no complaints of a Carter BBD on a 2-barrel manifold.