Found this...big backfire thru the carb at end...sounds lean: http://www.youtube.com/watch?v=lW6r290tN9U&feature=relmfu
Looks like an Edelbrock AFB clone. Is it me or did that back fire happen as the throttle was closing? If so, wouldn't the mixture go rich?
Found a longer version of that at the end after watching.. http://www.youtube.com/watch?v=s_FKWyv0XGI&feature=relmfu Watch the beginning, I think it explains it all... A nice qjet would be the answer tho..
Looks and sounds more like a timing issue.......that or the small lake of gas they poured in the intake finally ignited lol