my '02 (essentially stock) wr 426 backfires when i use the engine compression to slow down. am i too rich, too lean, something else? i'm currently running a 168 main, 40 pilot, clip in position #3 (7,000' altitude). i haven't adjusted the air screw from its stock position. the backfiring occurs more when the engine isn't completely hot but never really goes away. any thoughts?