most likely plugged or bad/wrong jet (no gogo juice) with the choke you are richining the mix (more gogo less air)and when you open it up it gets to lean(more air less gogo) I am sure art, ken, hrk, or the many others will chime in here shortly but you will need to let them know if there are any mods besides the s&s pipes style, air breather, which s&s is it was it running fine with this same configuration, or did it go belly up on you all of a sudden, does it get better when it is warmed or worse, what are the plugs telling you or have you pulled them yet, what octane of gas, and are any additives in it are you still on the gas from winter, so on so on and so on
