Jetting

[superchevy]

I know this is kind of a beaten subject but i have a 2001 400ex and its all stock except the k and n airfiter what size jets do you think should be in it due to the fact it dosent idle good and it backfires like crazy while comin down from speed... Any advice will help thanks

backfire on decceleration is the pilot jet and it being lean. get a pilot jet 1 size bigger and as for having in the K&N I would try maybe a 150 main