its backfiring... If its backfiring from the carburetor then that means your dist wire sequal is wrong. It could also be your timing if you said you got a brand new dist. Rotate engine to get #1 correct on dist. once you have that its easy after. I had the same problem but once i got my wires right it was too late for me. I kept trying to crank it and then later found out it was low cylinder compression. IF its not dist its your compression.