Idaho RX-7 Man

I have a 91 rx n\a that will run normal has good power and really doesn't have that many problems that I can find. It does however bogg out really bad sometimes it will spit out black smoke out of the exhaust and sometimes a flame will even shoot out of it. It just started doing this about a month ago win I put in some new python primary injectors so I changed them back to stock and it still does it sometimes. Its really pissing me OFF!! please help if you can