Motorcycle Repair: yamaha350 bigbear, air passages, bigbear

Question
i have a 98 bigbear 350 my brother has had it and he abused it the airfilter wass rust it is backfirinf throught the carb the intake manifold was towrn in two and i replaced it thinking that would stop the backfiring it has reduced it but continues and when i try to give it gas it want to shutdown but will idle fine any sugestions on what to check or do?

Answer
Try this, pull the carb and go through it and make sure its clean as the air filter may have let in dirt and grit plugging some air passages. While down check the valves and the clearances to make sure they are not to tight. Reinstall the carb and make sure the air cleaner is good and the intake is sealed. Put in a fresh spark plug and try this now it should only need a little adjustment to smooth it out.