i have a 04 400ex it idels fine when choked then stalls when i take it off...and it keeps backin fireing threrw that carb at lower rpms and sometimes the exhaust....i cleaned the carb and turned the ait/fuel out a turn incase it was to lean but didnt help

 

Has the bike been sitting at all ? it sounds like your pilot jet is clogged. Or possibly your valves are out of adjustment or a timing problem but I would bet that the pilot circuit is plugged up.