timing sounds like its quite a bit off, although i have never had that bad of issues with backfiring when the timing was off....have u recently done anything to the distributer or timing chain? did it just all of a sudden happen? worst case is that the timing chain skiped a tooth or is really loose...really loose sounds like the most likely of the two though..but check everything else that u can before u go checking the timing chain..unless u dont mind the extra work just so u know for sure.
