Backfire through Carb

Hi All, Thanks for all the comments. So the things I have done to the engine: New timing chain (Sprocket is original), New timing cover, new fuel pump, new alternator, new carb, new distributor( tried a new one, still did it), spark plug wires had not been messed with before the problem started but are new, spark plugs are fairly new. I have checked all the easy stuff. I'll try and take a look at the valves this weekend. I just had hernia repair surgery so I'm kinda limited on what I can do right now. Thanks again for all the suggestions on what the problems might be.