SO my sbc 350 is running very rough and choppy. I did a head gasket change and when i reassembled it, it sounds bad. checked the timing, the valve sequences, it idles for a little bit and sounds more like a lawn mower or a motorcycle than a chevy engine. the Carb backfires and ive seen flames a few times and can smell burning oil. i feel like this whole swab job has been a big mess and i dont know where i went wrong. Please, any suggestions or solutions. Thanks!