Fuel delivery problems, NEED HELP!!

I have a 1970 4dr dart with a 225. the carb is a holley 1920 and the car is equiped with the CAP clean air package. no egr, just the two valves in the air cleaner. anyways, the car ran fine when I first bought it 3 months ago. then over a period of a month, it started to run rough, like its not getting enough fuel. i changed the fuel filter n there was some sediment in it. i assume theres still probably sediment in the tank although the recent fuel filter appears to be clean. the other day it was cutting out so bad i couldnt accelerate, so i put it in nuetral n revved the engine. the first couple pumps i saw a lil black smoke in the exhaust, but the third pump produced a backfire and a big puff of blacksmoke. after the backfire it ran fine the rest of the day. it ran fine for 3 days n now its starting to get progressivly worse again. under accelleration it feels like im runnin outta gas, sputtering n what not. i pulled the plugs n they are all dry and tan in color.(thought it mite be runnin rich) theres a butterfly valve between the intake n exhaust manifolds, which seemed to be sticking. i sprayed some penetrating oil on the shaft and its not stickin anymore. im thinking the carb mite need a rebuild but im confused as to why it wil run fine some times n rough others. anyone have any advice as to what i can try?