New carb and intake and weird idle

on my 74 dart sport with a 318/904 I just swapped the factory 2 barrel for an edelbrock performer intake and and a edelbrock 650 avs 2 carb. Car starts and drives great. Only issue is when idling for a few minutes once its warmed up the idle will drop about 300 rpm for about 15 seconds and then go back to normal setting for a few minutes and then it drops 300 rpm for 15 seconds and repeat this process. Lol. Does it in park and drive. Also once warm if you power break it a little bit and let off it wants to die. Sometimes it does die. Any ideas? Thanks